JP5297519B2 - Manufacturing method of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a semiconductor device capable of forming a quantum dot having high crystal quality in high density. <P>SOLUTION: A manufacturing method of a semiconductor device comprises: a step of forming a quantum dot 16 on a ground layer 10 by self-organizing growth; a step of irradiating a surface of the ground layer 10 with Sb or GaSb before or when performing the step of forming the quantum dot 16; a step of removing an InSb layer 18 including Sb precipitated on a surface of the quantum dot 16 by etching the surface of the quantum dot 16 with an As raw material gas; and a step of growing a cap layer 22 on the quantum dot 16 from which the InSb layer 18 was removed. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device in which quantum dots are formed by self-organized growth.

  In recent years, research has been actively conducted on semiconductor devices using quantum dots, for example, quantum dot lasers in which quantum dots are introduced into an active layer of a semiconductor laser.

  As a technique for forming a quantum dot used in a quantum dot laser or the like, a technique for forming a quantum dot by self-organized growth is known. This uses a phenomenon in which quantum dots having a three-dimensional microstructure are self-formed by vapor phase epitaxial growth of a lattice-mismatched semiconductor under certain conditions.

  Several formation modes are known for the self-formation of quantum dots. Among them, the most known formation mode is a mode called Stranski-Krastanow mode (SK mode). The SK mode is a mode in which a semiconductor crystal to be epitaxially grown grows two-dimensionally (film growth) at the beginning of growth, but grows three-dimensionally when the elastic limit of the film is exceeded. By epitaxially growing a film having a larger lattice constant than the underlying material, quantum dots made of three-dimensional growth islands are self-formed.

However, the conventional quantum dot laser in which quantum dots are formed by self-organized growth has an inefficient quantum dot density of 5 × 10 ¹⁰ cm ⁻² or less, so that it cannot perform high-speed direct modulation of 10 Gbps or more. Had. Therefore, a new quantum dot growth method has been proposed in order to improve the density of the quantum dots. As one of such new quantum dot growth methods, a method of irradiating Sb to an underlying semiconductor layer on which quantum dots are grown before the quantum dots are grown has been proposed.

  A conventional quantum dot growth method in which Sb is irradiated on the underlying semiconductor layer on which quantum dots are grown will be described with reference to FIG. In the following, a case where quantum dots made of InAs are grown on an underlayer made of GaAs will be described.

  First, the surface of the underlayer 100 made of GaAs is irradiated with Sb. Thereby, an Sb layer 102 of about one atomic layer (monolayer, ML) is formed on the surface of the underlayer 100 (FIG. 31A).

  Next, a quantum dot layer 104 made of InAs is grown on the base layer 100 with the Sb layer 102 formed on the surface, for example, by MOCVD. Since InAs has a lattice constant different from that of GaAs of the underlayer 100, quantum dots 106 are formed in the quantum dot layer 104 by the SK mode (FIG. 31B).

  During the growth of the quantum dot layer 104, Sb on the surface of the underlayer 100 interdiffuses with As of InAs, which is the material of the quantum dot layer 104, and precipitates on the surface of the quantum dot layer 104. Thus, a surface layer containing Sb, for example, the InSb layer 108 is formed on the surface of the quantum dot layer 104 (FIG. 31C).

Next, a cap layer 110 made of GaAs is grown on the quantum dot layer 104 having the InSb layer 108 formed on the surface so as to embed the quantum dots 106 by MOCVD, for example (FIG. 31D).
JP 2005-093553 A JP 2004-335665 A JP-A-6-204498

  According to the quantum dot growth method shown in FIG. 31 described above, it is known that the density of quantum dots can be increased by about two times compared to the conventional method. On the other hand, however, the crystal quality of the quantum dots deteriorates and the luminous efficiency of the quantum dots decreases.

  Further, in a quantum dot laser using a quantum dot layer as an active layer, an active layer is formed by stacking quantum dot layers. However, as the number of stacked quantum dot layers increases, the underlying strain accumulates, so the quantum dot size distribution and density in the upper quantum dot layer are significantly different from the lower quantum dot layer, and defects may occur. There was inconvenience such as doing.

  Further, in the conventional quantum dot laser, it is necessary to grow the cladding layer at a relatively low growth temperature of, for example, about 600 ° C. so as not to destroy the quantum dots. However, when the cladding layer is grown at such a low growth temperature, the roughness of the interface between the semiconductor layer adjacent to the cladding layer such as the SCH (Separate Confinement Heterostructure) layer, the active layer, and the contact layer and the cladding layer is low. It had increased. As a result, there is a disadvantage that the light scattering loss increases.

  An object of the present invention is to provide a method for manufacturing a semiconductor device capable of forming quantum dots having high crystal quality at high density.

  Another object of the present invention is to provide a method of manufacturing a semiconductor device capable of repeatedly forming a plurality of quantum dot layers while maintaining a uniform size distribution and density of the quantum dots between the layers without causing defects. There is to do.

  Still another object of the present invention is to provide a cladding layer and a contact layer with high crystal quality without deteriorating the emission characteristics of the quantum dots when a quantum dot layer is used as the active layer of the optical semiconductor device. It is an object of the present invention to provide a method for manufacturing a semiconductor device that can be grown on.

According to one aspect of the present invention, on the underlayer, the step of forming quantum dots by self-organized growth, and before the step of forming the quantum dots or during the step of forming the quantum dots, After the step of irradiating the surface of the formation with Sb or GaSb and the step of forming the quantum dots, the surface of the quantum dots is irradiated with an As source gas for a certain time or the surface of the quantum dots is etched, After the step of removing the surface layer containing Sb deposited on the surface of the quantum dots, the step of removing the surface layer, the step of irradiating the surface of the quantum dots with the organic Sb source gas, and the organic Sb source gas And a step of growing a cap layer on the quantum dots after the step of irradiating the semiconductor device.

Further, according to another aspect of the embodiment , a step of growing a quantum dot layer including quantum dots formed by self-organized growth; and before the step of growing the quantum dot layer or growing the quantum dot layer Irradiating the surface of the underlayer of the quantum dot layer with Sb or GaSb during the step of forming ; and , after forming the quantum dot layer, irradiate the surface of the quantum dot with an As source gas for a certain period of time. Or removing the surface layer containing Sb deposited on the surface of the quantum dots by etching the surface of the quantum dots; and after removing the surface layer, organic Sb on the surface of the quantum dots. step that irradiates the raw material gas; after the step of irradiating the organic Sb raw material gas, on the quantum dot layer, by repeating the step of growing a capping layer, a semiconductor substrate , Forming an active layer including n layers (n is an integer of 2 or more) of the quantum dot layers, and in the step of forming the active layer, the i-th layer (i is 1 ≦ i ≦ n−1). A semiconductor device manufacturing method is provided in which the V / III ratio at the time of growth of the (i + 1) th quantum dot layer is set higher than the V / III ratio at the time of growth of the quantum dot layer. .

  According to the present invention, since the coating layer containing Sb is formed by irradiating the surface of the quantum dot with the organic Sb source gas, it is possible to maintain the shape of the quantum dot and lengthen the emission wavelength of the quantum dot. it can.

  In addition, according to the present invention, in the method of manufacturing a semiconductor device including the step of irradiating the surface of the underlayer with Sb or GaSb before the step of forming the quantum dots or in the step of forming the quantum dots, Since the surface layer containing Sb deposited on the surface of the quantum dot is removed by etching the surface of the quantum dot with the As source gas before the step of growing the cap layer after the step of forming High quality quantum dots can be formed at high density.

  Further, according to the present invention, since the cap layer is grown at a growth rate of 0.275 nm / s or less sufficient for Sb on the surface of the quantum dot to diffuse to the outermost surface of the cap layer, the crystal quality of the quantum dot is reduced. Can be improved.

  Further, according to the present invention, in the step of forming an active layer including n quantum dot layers (n is an integer of 2 or more), the i-th layer (i is an integer satisfying 1 ≦ i ≦ n−1) Since the V / III ratio during the growth of the (i + 1) th quantum dot layer is set higher than the V / III ratio during the growth of the quantum dot layer, the size distribution and density of the quantum dots can be reduced without causing defects. A plurality of quantum dot layers can be formed repeatedly while being kept uniform between the layers.

  Further, according to the present invention, the cladding layer is grown using trimethyl gallium as a Ga raw material on the active layer containing the quantum dots at a growth temperature of 610 to 660 ° C. A flat upper clad layer having a high crystal quality and a flatness can be grown without dot destruction.

  Further, according to the present invention, the contact layer is grown on the clad layer using triethylgallium as a Ga material at a growth temperature of 600 to 610 ° C., so that deterioration of the light emission characteristics of the quantum dots and destruction of the quantum dots can be achieved. A contact layer with high crystal quality can be grown without this.

[Principle of the present invention]
First, the principle of the present invention will be described.

  The conventional quantum dot growth method of irradiating the surface of the underlayer on which quantum dots are grown before the quantum dots are grown has an advantage that the density of the quantum dots can be increased. On the other hand, there is a disadvantage that the crystal quality of the quantum dots deteriorates and the luminous efficiency decreases.

  The inventors of the present application have conducted experimental research on this cause, and there is a defect in a surface layer containing Sb such as an InSb layer formed by the precipitation of Sb on the surface of the quantum dot layer during the growth of the quantum dot layer. The result of being present.

  FIG. 1 is a schematic cross-sectional view for explaining defects generated in the conventional quantum dot growth method shown in FIG. In the conventional quantum dot growth method, as shown in the figure, Sb is deposited on the surface of the quantum dot layer 104 while the quantum dot layer 104 is grown, and a surface layer containing Sb, for example, an InSb layer 108 is formed. The InSb layer 108 has a defect as indicated by a cross in the figure.

  Such an InSb layer 108 affects the crystal quality of the quantum dots 104 and is considered to cause a decrease in light emission efficiency. Therefore, by removing Sb deposited on the surface of the quantum dot layer 104, quantum dots with high crystal quality can be formed with high density.

  The method for manufacturing a semiconductor device according to the present invention is based on such knowledge, and has one of the main characteristics that includes a step of removing Sb deposited on the surface of the quantum dot layer. An outline of a method for manufacturing a semiconductor device according to the present invention will be described below with reference to FIGS. 2 and 3 are process cross-sectional views for explaining the outline of the semiconductor device manufacturing method according to the present invention.

  First, the surface of the underlayer 10 made of GaAs is irradiated with Sb, for example, by irradiating an organic Sb source gas. As a result, an Sb layer 12 of about 1 ML, for example, is formed on the surface of the base layer 10 (FIG. 2A). The quantum dots can be grown at a high density by irradiating the surface of the underlayer 10 with Sb before the quantum dots are grown. Instead of Sb irradiation, the surface of the underlayer 10 may be irradiated with GaSb. Further, Sb or GaSb may be applied to the surface of the underlayer 10 during the growth of quantum dots.

  Next, a quantum dot layer 14 made of InAs is grown on the underlayer 10 having the Sb layer 12 formed on the surface. Since InAs has a lattice constant different from that of GaAs of the underlayer 10, quantum dots 16 are formed in the quantum dot layer 14 by self-organized growth called SK mode (FIG. 2B).

  During the growth of the quantum dot layer 14, Sb on the surface of the underlayer 10 interdiffuses with As of InAs, which is the material of the quantum dot layer 14, and precipitates on the surface of the quantum dot layer 14. Thus, a surface layer containing Sb, for example, an InSb layer 18 is formed on the surface of the quantum dot layer 14 (FIG. 2C).

Next, the surface of the quantum dot layer 14 on which the InSb layer 18 is formed is irradiated with an As raw material for a predetermined time, and the surface of the quantum dot layer 14 is etched with an As raw material gas (FIG. 2D). As the As raw material irradiated for a certain period of time, for example, tertiary butylarsine (TBA), AsH ₃ , As ₂ , As ₄ can be used. Thereby, the InSb layer 18 on the surface of the quantum dot layer 14 is removed (FIG. 3A).

  As described above, in the method of manufacturing a semiconductor device according to the present invention, the surface of the quantum dot layer 14 on which the InSb layer 18 is formed is irradiated with the As source gas for a predetermined time, and the surface of the quantum dot layer 14 is etched with the As source gas. There is one of the main features. Since the InSb layer 18 is removed by etching using the As source gas, defects of the quantum dots 16 can be reduced and the crystal quality of the quantum dots 16 can be improved.

  Next, the surface of the quantum dot layer 14 is irradiated with an organic Sb source gas and a group III metal (In, Ga, Al) organic source gas at the same time. Thereby, the coating layer 20 containing a group III metal (In, Ga, Al) and Sb is formed on the surface of the quantum dot layer 14 (FIG. 3B). Specifically, the coating layer 20 containing a Group III metal and Sb is made of InSb, GaSb, AlSb, or a mixed crystal thereof.

  As described above, the semiconductor device manufacturing method according to the present invention is also mainly characterized in that the surface of the quantum dot layer 14 is irradiated with the organic Sb source gas and the organic source gas of group III metal (In, Ga, Al). There is one.

  Since the surface of the quantum dot 16 is covered with the coating layer 20 made of InSb or the like, the shape of the quantum dot 16 is maintained and the emission wavelength of the quantum dot 16 is increased in the subsequent step of growing the cap layer 22. be able to.

  The coating layer 20 made of Sb may be formed by irradiating the organic Sb source gas alone without irradiating the group III metal organic source gas.

  Next, a cap layer 22 made of GaAs is grown on the quantum dot layer 14 having the coating layer 20 formed on the surface so as to embed the quantum dots 16 (FIG. 3C).

  During the growth of the cap layer 22, Sb of the coating layer 20 interdiffuses with As of GaAs which is the material of the cap layer 22 and precipitates on the surface of the cap layer 22. Thus, a surface layer containing Sb, for example, a GaSb layer 24 is formed on the surface of the cap layer 22 (FIG. 3C).

  Here, the semiconductor device manufacturing method according to the present invention also grows the cap layer 22 at a growth rate low enough to allow Sb to diffuse to the outermost surface of the cap layer 22 in the step of growing the cap layer 22. There are main characteristics. Specifically, the cap layer 22 is grown at a growth rate of 0.275 nm / s or less. Thereby, Sb on the surface of the quantum dot layer 14 can be sufficiently removed.

  In the present invention, after the step of growing the quantum dot layer 14 shown in FIGS. 2A and 2C, the As source gas shown in FIGS. 2D and 3A is supplied for a certain period of time. You may perform the process of growing the cap layer 22, without performing the process of irradiating, and the process of forming the coating layer 20 shown in FIG.3 (b). Even in this case, Sb deposited on the surface of the quantum dot layer 14 can be sufficiently removed by growing the cap layer 22 at a growth rate of 0.275 nm / s or less. Thus, Sb can be sufficiently removed also by growing the cap layer 22 at a low growth rate, and the crystal quality of the quantum dots 16 can be improved.

  Thus, according to the method for manufacturing a semiconductor device according to the present invention, quantum dots 16 having high crystal quality can be grown at high density.

The quantum dots 16 in the semiconductor device according to the present invention thus manufactured have a density of, for example, 5 × 10 ¹⁰ cm ⁻² or more, and an emission wavelength of, for example, a long wavelength of 1.3 μm or more.

  Further, when the step of forming the coating layer 20 shown in FIG. 3B is performed, the interface between the quantum dot layer 14 and the cap layer 22 has the following structural features.

  That is, even when the cap layer 22 is grown at a low growth rate, the coating layer 20 between the quantum dot layer 14 and the cap layer 22 may not be completely removed. In this case, between the quantum dot layer 14 and the cap layer 22, as shown in FIG. 4, a thin film 21 containing a group III metal and Sb, that is, InSb, GaSb, AlSb, or a mixed crystal thereof. The thin film 21 remains. The film thickness of the thin film 21 is, for example, 0.5 to 1 ML.

  Hereinafter, the present invention will be described with reference to embodiments.

[First Embodiment]
A method of manufacturing the semiconductor device according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a graph showing the partial pressure of the source gas supplied in the semiconductor device manufacturing method according to the present embodiment, FIG. 6 is a process cross-sectional view illustrating the semiconductor device manufacturing method according to the present embodiment, and FIG. It is a graph which shows PL emission spectrum at the room temperature of the quantum dot in the case where Sb irradiation is performed later.

  In the method for manufacturing the semiconductor device according to the present embodiment, metal organic chemical vapor deposition (MOCVD) is used for crystal growth.

  First, the GaAs substrate 26 is accommodated in the reaction chamber of the MOCVD apparatus.

  Next, the substrate temperature is set to 700 ° C., for example, and TBA and trimethylgallium (TMG) are supplied into the reaction chamber (time interval t1 in FIG. 5). Thereby, a buffer layer 28 made of GaAs is grown on the GaAs substrate 26 (FIG. 6A).

  Next, the supply of TMG is stopped, and the substrate temperature is gradually lowered to, for example, 500 ° C. (time interval t2 in FIG. 5). During this time, the supply of TBA continues.

  Next, the TBA partial pressure is lowered and the supply of TBA is continued (time interval t3 in FIG. 5). During this time, the substrate temperature is maintained at 500 ° C., for example.

  Next, while maintaining the substrate temperature at, for example, 500 ° C., the supply of TBA is continued, and trimethylindium (TMI) is supplied into the reaction chamber (time interval t4 in FIG. 5). Thus, on the buffer layer 28, for example, InAs corresponding to 2.64 ML is grown at a growth rate of 0.011 ML / s, for example, the quantum dot layer 30 made of InAs is grown. Since InAs and GaAs of the buffer layer 28 have different lattice constants, quantum dots 32 are formed in the quantum dot layer 30 by self-organized growth called SK mode (FIG. 6B).

  Next, the supply of TMI is stopped, while the supply of TBA is continued (time interval t5 in FIG. 5). During this time, the substrate temperature is maintained at 500 ° C., for example.

  Next, the supply of TBA is stopped while maintaining the substrate temperature at, for example, 500 ° C., and trimethylantimony (TMSb) is supplied into the reaction chamber (time interval t6 in FIG. 5). Thus, by irradiating the surface of the quantum dot layer 30 with TMSb, the Sb layer 34 is formed on the surface of the quantum dot layer 30 (FIG. 6C).

  Next, while maintaining the substrate temperature at, for example, 500 ° C., the partial pressure is increased to restart the supply of TBA, and triethylgallium (TEG) is supplied into the reaction chamber (time interval t7 in FIG. 5). Thereby, a cap layer 36 made of GaAs is grown on the quantum dot layer 30 so as to embed the quantum dots 32 (FIG. 6D).

  During the growth of the cap layer 36, Sb of the Sb layer 34 formed on the surface of the quantum dot layer 30 interdiffuses with As of GaAs, which is the material of the cap layer 36, and precipitates on the surface of the cap layer 36. . Thus, the GaSb layer 38 is formed on the surface of the cap layer 36.

  The semiconductor device manufacturing method according to the present embodiment includes a step of irradiating the surface of the quantum dot layer 30 with TMSb after the step of growing the quantum dot layer 30 and before the step of growing the cap layer 36. There is.

  Since the surface of the quantum dot 32 is covered with the Sb layer 34 formed by irradiating TMSb, the shape of the quantum dot 32 can be maintained in the step of growing the cap layer 36. Thereby, the light emission wavelength of the quantum dot 32 can be lengthened.

  FIG. 7 is a graph showing a PL emission spectrum of a quantum dot at room temperature when TMSb is irradiated after the growth of the quantum dot. In the figure, the spectrum indicated by ▲ is a PL emission spectrum obtained for a sample in which the TMSb irradiation time is 2 seconds and the growth rate of the cap layer made of GaAs is 0.1375 nm / s. The spectrum indicated by ◯ is a PL emission spectrum obtained for a sample in which the TMSb irradiation time is 2 seconds and the growth rate of the cap layer made of GaAs is 0.275 nm / s. The spectrum indicated by the broken line is a PL emission spectrum obtained for a standard sample in which the growth rate of the cap layer made of GaAs is 0.275 nm / s without irradiation with TMSb. In any sample, the quantum dots were formed by growing InAs corresponding to 2.64 ML at a growth rate of 0.011 ML / s. The spectra indicated by □ and ■ are described in the second embodiment.

  As is clear from the spectrum shown in FIG. 7, it can be seen that in the sample irradiated with TMSb after the growth of the quantum dots, the emission wavelength of the quantum dots is shifted to the longer wavelength side compared to the standard sample. Specifically, the peak emission wavelength of the standard sample is 1.308 μm. On the other hand, the peak emission wavelength of the sample irradiated with TMSb after the quantum dot growth is 1.357 μm when the growth rate of the cap layer is 0.1375 nm / s or 0.275 nm / s. However, the emission intensity of the sample irradiated with TMSb is lower than that of the standard sample. Between samples irradiated with TMSb, the decrease in emission intensity is more remarkable in the sample with a faster growth rate of the cap layer.

  As described above, according to the present embodiment, after the step of growing the quantum dot layer 30 and before the step of growing the cap layer 36, the surface of the quantum dot layer 30 is irradiated with TMSb to thereby form the quantum dots 32. Since the Sb layer 34 covering the surface is formed, the shape of the quantum dots 32 can be maintained and the emission wavelength of the quantum dots 32 can be increased.

[Second Embodiment]
A method for fabricating a semiconductor device according to the second embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a graph showing a partial pressure of a source gas supplied in the method for manufacturing a semiconductor device according to the present embodiment, and FIG. Note that the same components as those of the semiconductor device manufacturing method according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted or simplified.

  The semiconductor device manufacturing method according to the present embodiment is substantially the same as the semiconductor device manufacturing method according to the first embodiment. The manufacturing method of the semiconductor device according to the present embodiment is different from the manufacturing method of the semiconductor device according to the first embodiment in which TMSb is irradiated alone on the surface of the quantum dot layer 30 in that TMSb and TEG are simultaneously irradiated. .

  First, the buffer layer 28 made of GaAs and the quantum dot layer 30 made of InAs are grown on the GaAs substrate 26 in the same manner as the semiconductor device manufacturing method according to the first embodiment (time intervals t1 to t4 in FIG. FIG. 9A).

  Next, the supply of TMI is stopped, while the supply of TBA is continued (time interval t5 in FIG. 8). During this time, the substrate temperature is maintained at 500 ° C., for example.

  Next, while maintaining the substrate temperature at, for example, 500 ° C., the supply of TBA is stopped, and TMSb and TEG are supplied into the reaction chamber (time interval t6 in FIG. 8). In this way, by irradiating the surface of the quantum dot layer 30 with TMSb and TEG at the same time, the GaSb layer 40 is formed on the surface of the quantum dot layer 30 (FIG. 9B).

  Next, while maintaining the substrate temperature at, for example, 500 ° C., the partial pressure is increased to restart the supply of TBA, and the supply of TEG is continued (time interval t7 in FIG. 8). Thereby, a cap layer 36 made of GaAs is grown on the quantum dot layer 30 so as to embed the quantum dots 32 (FIG. 9C).

  During the growth of the cap layer 36, Sb of the GaSb layer 40 formed on the surface of the quantum dot layer 30 interdiffuses with As of GaAs, which is the material of the cap layer 36, and precipitates on the surface of the cap layer 36. . Thus, the GaSb layer 42 is formed on the surface of the cap layer 36.

  The semiconductor device manufacturing method according to the present embodiment includes a step of simultaneously irradiating the surface of the quantum dot layer 30 with TMSb and TEG after the step of growing the quantum dot layer 30 and before the step of growing the cap layer 36. It is characterized by having.

  Since the surface of the quantum dot 32 is covered with the GaSb layer 40 formed by simultaneously irradiating TMSb and TEG, the shape of the quantum dot 32 can be maintained in the step of growing the cap layer 36. Thereby, the light emission wavelength of the quantum dot 32 can be lengthened.

  FIG. 7 shows a PL emission spectrum of a quantum dot at room temperature when TMSb and TEG are simultaneously irradiated after the growth of the quantum dot, in addition to the PL emission spectrum described in the first embodiment. In the figure, the spectrum indicated by □ is a PL emission spectrum obtained for a sample in which the irradiation time of TMSb and TEG is 2 seconds and the growth rate of the cap layer made of GaAs is 0.275 nm / s. The spectrum indicated by (2) is a PL emission spectrum obtained for a sample in which the irradiation time of TMSb and TEG is 2 seconds and the growth rate of the cap layer made of GaAs is 0.1375 nm / s. Also in these samples, quantum dots were formed by growing InAs corresponding to 2.64 ML at a growth rate of 0.011 ML / s.

As is clear from the spectrum shown in FIG. 7, the sample irradiated with TMSb and TEG at the same time after the growth of quantum dots was also compared with the sample irradiated with TMSb alone. Is shifted to the longer wavelength side. Specifically, the peak emission wavelength of the sample irradiated with TMSb and TEG after quantum dot growth is 1.326 μm when the growth rate of the cap layer is 0.1375 nm / s, and the growth rate of the cap layer is 0. .
In the case of 275 nm / s, it is 1.344 μm. Compared with the sample irradiated with TMSb alone, the emission wavelength is shifted to the short wavelength side, but the sample irradiated with TMSb and TEG simultaneously has high emission intensity. When the growth rate of the cap layer is 0.1375 nm / s, light emission intensity comparable to that of the standard sample is obtained.

  Thus, according to the present embodiment, after the step of growing the quantum dot layer 30 and before the step of growing the cap layer 36, the surface of the quantum dot layer 30 is irradiated with TMSb and TEG simultaneously. Since the GaSb layer 40 that covers the surface of the quantum dot 32 is formed, the shape of the quantum dot 32 can be maintained and the emission wavelength of the quantum dot 32 can be increased. In addition, according to the present embodiment, it is possible to obtain a high emission intensity as compared with the semiconductor device manufacturing method according to the first embodiment in which the surface of the quantum dot layer 30 is irradiated with TMSb alone.

  Note that the semiconductor device manufactured by the semiconductor device manufacturing method according to the present embodiment has the following structural features at the interface between the quantum dot layer 30 and the cap layer 36.

  That is, even when the cap layer 36 is grown at a low growth rate, the GaSb layer 40 between the quantum dot layer 14 and the cap layer 22 may not be completely removed. In this case, a thin film made of GaSb remains between the quantum dot layer 30 and the cap layer 36.

[Third Embodiment]
A method for fabricating a semiconductor device according to the third embodiment of the present invention will be described with reference to FIGS. FIG. 10 is a graph showing the partial pressure of the source gas supplied in the semiconductor device manufacturing method according to the present embodiment, FIGS. 11 and 12 are process cross-sectional views showing the semiconductor device manufacturing method according to the present embodiment, and FIG. It is a graph which shows the relationship between the peak emission wavelength and emission intensity | strength of a dot, and the etching time by TBA. Note that the same components as those of the semiconductor device manufacturing method according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted or simplified.

  The semiconductor device manufacturing method according to the present embodiment grows the quantum dot layer 30 in the semiconductor device manufacturing method including the step of irradiating the surface of the buffer layer 28 with TMSb before the step of growing the quantum dot layer 30. After the step, before the step of growing the cap layer 36, the main feature is that the surface of the quantum dot layer 30 is further irradiated with TBA for a predetermined time and the surface of the quantum dot layer 30 is further etched with TBA. .

  First, the buffer layer 28 made of GaAs is grown on the GaAs substrate 26 in the same manner as in the semiconductor device manufacturing method according to the first embodiment (time interval t1 in FIG. 10).

  Next, the supply of TMG is stopped, and the substrate temperature is gradually lowered to, for example, 500 ° C. (time interval t2 in FIG. 10). During this time, the supply of TBA continues.

  Next, the TBA partial pressure is lowered and the supply of TBA is continued (time interval t3 in FIG. 10). During this time, the substrate temperature is maintained at 500 ° C., for example.

Next, while maintaining the substrate temperature at, for example, 500 ° C., the supply of TBA is stopped and TMSb is supplied into the reaction chamber (time interval t4 in FIG. 10). Thus, by irradiating the surface of the buffer layer 28 with TMSb, for example, an Sb layer 44 of about 1 ML is formed on the surface of the buffer layer 28 (FIG. 11A). Since the surface of the buffer layer 28 is irradiated with TMSb before the quantum dots are grown, the quantum dots can be grown at a density higher than 5 × 10 ¹⁰ cm ⁻² , for example.

  Next, while maintaining the substrate temperature at, for example, 500 ° C., the supply of TBA is restarted and TMI is supplied into the reaction chamber (time interval t5 in FIG. 10). Thus, the quantum dot layer 30 made of InAs is grown on the buffer layer 28. Since InAs and GaAs of the buffer layer 28 have different lattice constants, quantum dots 32 are formed in the quantum dot layer 30 by the SK mode (FIG. 11B).

  During the growth of the quantum dot layer 30, Sb on the surface of the buffer layer 28 interdiffuses with As of InAs, which is the material of the quantum dot layer 30, and precipitates on the surface of the quantum dot layer 30. Thus, the InSb layer 46 is formed on the surface of the quantum dot layer 30 (FIG. 11C).

  Next, the supply of TMI is stopped, while the supply of TBA is continued (time interval t6 in FIG. 10). During this time, the substrate temperature is maintained at 500 ° C., for example.

  Next, the partial pressure is increased and the supply of TBA is continued (time interval t7 in FIG. 10). In this way, the surface of the quantum dot layer 30 on which the InSb layer 46 is formed is irradiated with TBA for a predetermined time, and the surface of the quantum dot layer 30 is etched by TBA (FIG. 12A). Thereby, the InSb layer 46 on the surface of the quantum dot layer 30 is removed (FIG. 12B).

  As described above, the method of manufacturing the semiconductor device according to the present embodiment mainly irradiates the surface of the quantum dot layer 30 on which the InSb layer 46 is formed with TBA for a predetermined time and etches the surface of the quantum dot layer 30 with TBA. There are features. Since the InSb layer 46 is removed by etching with TBA, defects in the quantum dots 32 can be reduced and the crystal quality of the quantum dots 32 can be improved.

  Next, while maintaining the substrate temperature at 500 ° C., for example, the partial pressure is lowered to continue the supply of TBA, and TEG is supplied into the reaction chamber (time interval t8 in FIG. 10). Thereby, a cap layer 36 made of GaAs is grown on the quantum dot layer 30 so as to embed the quantum dots 32 (FIG. 12C).

  FIG. 13 is a graph showing the relationship between the peak emission wavelength and emission intensity of a quantum dot and the etching time by TBA. The horizontal axis of the graph indicates the etching time by TBA. The left vertical axis of the graph represents the peak emission wavelength, and the right vertical axis represents the emission intensity. The plots marked with ▲ and Δ show the peak emission wavelength and emission intensity of the quantum dots obtained for the sample irradiated with TMSb for 1 second before the growth of the quantum dots, respectively. The plots marked with (1) and □ show the peak emission wavelength and emission intensity of the quantum dots obtained for the standard sample not irradiated with TMSb before the growth of the quantum dots. The growth rate of the cap layer was set to 0.55 nm / s common to the samples.

  As shown in FIG. 13, in the case of the sample irradiated with TMSb before the growth of the quantum dots, if the etching by TBA is not performed, the emission intensity of the quantum dots is about 1/300 that of the standard sample. It is getting smaller. When etching with TBA is performed on a sample irradiated with such TMSb, the emission intensity of the quantum dots increases as the etching time with TBA increases. When etching with TBA is performed for 20 seconds or more, the light emission intensity of the quantum dots increases to about one-half that of the standard sample.

  Since the emission intensity is increased by performing etching with TBA, it is considered that defects due to Sb deposited on the surface of the quantum dots are reduced and the crystal quality of the quantum dots is improved.

  As described above, according to the present embodiment, in the method of manufacturing a semiconductor device including the step of irradiating the surface of the buffer layer 28 with TMSb before the step of growing the quantum dot layer 30, the step of growing the quantum dots 32. After that, before the step of growing the cap layer 36, the surface of the quantum dot layer 30 is irradiated with TBA for a certain period of time, and the surface of the quantum dot layer 30 is etched by TBA, so that the InSb layer 46 is removed. The quantum dots 32 having crystal quality can be formed with high density.

[Fourth Embodiment]
A method of manufacturing a semiconductor device according to the fourth embodiment of the present invention will be described with reference to FIGS. FIG. 14 is a graph showing PL emission spectra at room temperature of quantum dots obtained for samples with different cap layer growth rates, and FIG. 15 is a schematic cross-sectional view for explaining Sb diffusion in the method of manufacturing a semiconductor device according to the present embodiment. It is. Note that the same components as those of the semiconductor device manufacturing method according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted or simplified.

  The manufacturing method of the semiconductor device according to the present embodiment is sufficient for Sb on the surface of the quantum dot layer 30 to diffuse into the outermost surface of the cap layer 36 in the step of growing the cap layer 36 after the quantum dot layer 30 is grown. The main feature is that the cap layer 36 is grown at a high growth rate, specifically, at a growth rate of 0.275 nm / s or less.

  FIG. 14 is a graph showing PL emission spectra at room temperature of quantum dots obtained for samples with different cap layer growth rates.

  The sample used for the measurement of the PL emission spectrum is obtained by growing a cap layer made of GaAs on a quantum dot having Sb deposited on the surface. The quantum dots were formed by growing InAs corresponding to 2.64 ML at a growth rate of 0.011 ML / s on a buffer layer made of GaAs whose surface was irradiated with TMSb for 1 second. As a standard sample, a sample in which quantum dots were formed on the surface of the buffer layer without irradiating TMSb was prepared.

  In the figure, the spectrum indicated by □ is a PL emission spectrum obtained for a sample having a cap layer grown at a growth rate of 0.275 nm / s on a quantum dot having Sb deposited on the surface. The spectrum indicated by (2) is a PL emission spectrum obtained for a sample having a cap layer grown at a growth rate of 0.55 nm / s on a quantum dot having Sb deposited on the surface. A spectrum indicated by a broken line is a PL emission spectrum obtained for a standard sample having a cap layer grown on a quantum dot at a growth rate of 0.275 nm / s.

  As is clear from FIG. 14, in the case of a sample in which a cap layer is grown at a growth rate of 0.55 nm / s on a quantum dot having Sb deposited on the surface, the emission wavelength is shifted to the longer wavelength side compared to the standard sample. ing. However, the emission intensity is about 1/900 that of the standard sample.

  In contrast, in the case of a sample in which the cap layer is grown at a growth rate of 0.275 nm / s on a quantum dot on which Sb is deposited on the surface, the luminescence intensity is the growth rate of the cap layer. Is increased to the same level or higher than that of a standard sample having the same value. Further, the emission wavelength remains shifted to the longer wavelength side compared to the standard sample.

  The above result is considered to be because the diffusion of Sb on the surface of the quantum dot is influenced by the growth rate of the cap layer.

  FIG. 15A is a schematic cross-sectional view showing the state of Sb when a cap layer is grown at a growth rate of 0.55 nm / s.

  When the growth rate of the cap layer 36 is 0.55 nm / s, Sb on the surface of the quantum dot 32 cannot be efficiently interdiffused with As of GaAs that is the material of the cap layer 36 because the growth rate is high. . For this reason, Sb remains on the surface of the quantum dot 32.

  Thus, interdiffusion between Sb and As, which is suppressed when the growth rate of the cap layer 36 is high, is promoted by reducing the growth rate of the cap layer 36.

  When the growth rate of the cap layer 36 is 0.275 nm / s, it is considered that Sb has diffused to the outermost surface of the cap layer 36. In this case, the state shown in FIG. 15B or FIG. 15C is considered as the state of Sb. FIGS. 15B and 15C are schematic cross-sectional views showing the state of Sb when the cap layer is grown at a growth rate of 0.275 nm / s.

  First, as shown in FIG. 15B, a state where Sb diffused to the outermost surface of the cap layer 36 and Sb remaining in the cap layer 36 are mixed is conceivable.

  Alternatively, as shown in FIG. 15C, a state where Sb completely diffuses to the outermost surface of the cap layer 36 is conceivable.

  Thus, by growing the cap layer 36 at a low growth rate of 0.275 nm / s or less, Sb on the surface of the quantum dot 32 diffuses into the outermost surface of the cap layer 36. Thereby, the crystal quality of the quantum dots 32 is improved, and high emission intensity is realized.

  The semiconductor device manufacturing method according to the present embodiment is sufficient for Sb on the surface of the quantum dots 32 to diffuse to the outermost surface of the cap layer 36 in the step of growing the cap layer 36 after the quantum dot layer 30 is grown. Since the cap layer 36 is grown at a growth rate of 0.275 nm / s or less, the crystal quality of the quantum dots 32 can be improved and high emission intensity can be realized.

  In the semiconductor device manufacturing method according to the first and second embodiments, the cap layer 36 may be grown at a growth rate of 0.275 nm / s or less as described above. Thereby, even when the surface of the quantum dot layer 30 is irradiated with Sb or GaSb, the crystal quality of the quantum dots 32 can be improved and high emission intensity can be realized.

  Also in the semiconductor device manufacturing method according to the third embodiment, the cap layer 36 may be grown at a growth rate of 0.275 nm / s or less as described above. Thereby, Sb on the surface of the quantum dot layer 30 can be more reliably removed, the crystal quality of the quantum dots 32 can be improved, and high emission intensity can be realized.

[Fifth Embodiment]
A method for fabricating a semiconductor device according to the fifth embodiment of the present invention will be explained with reference to FIGS. FIG. 16 is a graph showing the partial pressure of the source gas supplied in the semiconductor device manufacturing method according to the present embodiment, and FIGS. 17 and 18 are process cross-sectional views showing the semiconductor device manufacturing method according to the present embodiment. Note that the description of the same components as those of the semiconductor device manufacturing method according to the first to fourth embodiments is omitted or simplified.

  The semiconductor device manufacturing method according to the present embodiment is the same as that of the semiconductor device manufacturing method according to the third embodiment, after the step of irradiating TBA for a certain period of time and before the step of growing the cap layer 36. Similar to the device manufacturing method, the surface of the quantum dots 32 is irradiated with GaSb. Further, in the step of growing the cap layer 36, the cap layer 36 is grown at a low growth rate as in the method of manufacturing the semiconductor device according to the fourth embodiment.

  First, the buffer layer 28 made of GaAs is grown on the GaAs substrate 26 in the same manner as in the semiconductor device manufacturing method according to the first embodiment (time interval t1 in FIG. 16).

  Next, the supply of TMG is stopped, and the substrate temperature is gradually lowered to, for example, 500 ° C. (time interval t2 in FIG. 16). During this time, the supply of TBA continues.

  Next, the TBA partial pressure is lowered and the supply of TBA is continued (time interval t3 in FIG. 16). During this time, the substrate temperature is maintained at 500 ° C., for example.

Next, while maintaining the substrate temperature at, for example, 500 ° C., the supply of TBA is stopped and TMSb is supplied into the reaction chamber (time interval t4 in FIG. 16). Thus, by irradiating the surface of the buffer layer 28 with TMSb, an Sb layer 44 of about 1 ML, for example, is formed on the surface of the buffer layer 28 (FIG. 17A). Since the surface of the buffer layer 28 is irradiated with TMSb before the quantum dots are grown, the quantum dots can be grown at a density higher than 5 × 10 ¹⁰ cm ⁻² , for example.

  Next, while maintaining the substrate temperature at, for example, 500 ° C., the supply of TBA is resumed and TMI is supplied into the reaction chamber (time interval t5 in FIG. 16). Thus, the quantum dot layer 30 made of InAs is grown on the buffer layer 28. Since InAs and GaAs of the buffer layer 28 have different lattice constants, quantum dots 32 are formed in the quantum dot layer 30 by the SK mode (FIG. 17B).

  During the growth of the quantum dot layer 30, Sb on the surface of the buffer layer 28 interdiffuses with As of InAs, which is the material of the quantum dot layer 30, and precipitates on the surface of the quantum dot layer 30. Thus, the InSb layer 46 is formed on the surface of the quantum dot layer 30 (FIG. 17C).

  Next, the supply of TMI is stopped, while the supply of TBA is continued (time interval t6 in FIG. 16). During this time, the substrate temperature is maintained at 500 ° C., for example.

  Next, the partial pressure is increased and the supply of TBA is continued (time interval t7 in FIG. 16). In this way, the surface of the quantum dot layer 30 on which the InSb layer 46 is formed is irradiated with TBA for a predetermined time, and the surface of the quantum dot layer 30 is etched by TBA (FIG. 17D). Thereby, the InSb layer 46 on the surface of the quantum dot layer 30 is removed (FIG. 18A). As in the semiconductor device manufacturing method according to the third embodiment, since the InSb layer 46 is removed by TBA etching, defects in the quantum dots 32 can be reduced and the crystal quality of the quantum dots 32 can be improved.

  Next, while maintaining the substrate temperature at, for example, 500 ° C., the supply of TBA is stopped, and TMSb and TEG are supplied into the reaction chamber (time interval t8 in FIG. 16). Thus, by simultaneously irradiating the surface of the quantum dot layer 30 with TMSb and TEG, the GaSb layer 40 is formed on the surface of the quantum dot layer 30 (FIG. 18B). Similar to the method of manufacturing the semiconductor device according to the second embodiment, before the step of growing the cap layer 36, the surface of the quantum dot layer 30 is irradiated with TMSb and TEG simultaneously, so that the emission wavelength of the quantum dots 32 is increased. Higher emission intensity can be obtained as the wavelength is changed. Note that TMSb may be irradiated alone as in the semiconductor device manufacturing method according to the first embodiment.

  Next, while maintaining the substrate temperature at, for example, 500 ° C., the supply of TBA is resumed and the supply of TEG is continued (time interval t9 in FIG. 16). Thereby, a cap layer 36 made of GaAs is grown on the quantum dot layer 30 so as to embed the quantum dots 32 (FIG. 18C).

  During the growth of the cap layer 36, Sb of the GaSb layer 40 formed on the surface of the quantum dot layer 30 interdiffuses with As of GaAs, which is the material of the cap layer 36, and precipitates on the surface of the cap layer 36. . Thus, the GaSb layer 42 is formed on the surface of the cap layer 36.

  Here, the cap layer 36 is grown at a growth rate of, for example, 0.275 nm / s or less, as in the method of manufacturing the semiconductor device according to the fourth embodiment. Since the cap layer 36 is grown at a growth rate sufficient for Sb on the surface of the quantum dot 32 to diffuse to the outermost surface of the cap layer 36, the crystal quality of the quantum dot 32 can be improved and high emission intensity can be realized. it can.

Thus, the quantum dots 32 in the semiconductor device manufactured by the semiconductor device manufacturing method according to the present embodiment have a density of, for example, 5 × 10 ¹⁰ cm ⁻² or more, and an emission wavelength of, for example, a long wavelength of 1.3 μm or more. ing.

[Sixth Embodiment]
A semiconductor device and a manufacturing method thereof according to the sixth embodiment of the present invention will be described with reference to FIGS. FIG. 19 is a sectional view showing the structure of the semiconductor device according to the present embodiment. FIGS. 20 and 21 are process sectional views showing the method for manufacturing the semiconductor device according to the present embodiment. Note that the description of the same components as those of the semiconductor device manufacturing method according to the fifth embodiment is omitted or simplified.

  In the present embodiment, a ridge type quantum dot laser in which quantum dots 32 grown by the semiconductor device manufacturing method according to the fifth embodiment are applied to an active layer of a semiconductor laser will be described.

On the n-GaAs substrate 50, for example, a buffer layer 52 made of n-GaAs having an impurity concentration of 1 × 10 ¹⁸ cm ⁻³ is formed. The concentration of the n-type impurity introduced into the n-GaAs substrate 50 is, for example, 1 × 10 ¹⁸ cm ⁻³ . The concentration of the n-type impurity introduced into the buffer layer 52 is, for example, 1 × 10 ¹⁸ cm ⁻³ .

A lower cladding layer 54 made of n-Al _0.3 Ga _0.7 As is formed on the buffer layer 52. The concentration of the n-type impurity introduced into the lower cladding layer 54 is, for example, 5 × 10 ¹⁷ cm ⁻³ . The film thickness of the lower cladding layer 54 is, for example, 3 μm.

An active layer 56 is formed on the lower cladding layer 54. The film thickness of the active layer 56 is, for example, 0.5 μm. In the active layer 56, a multilayer film of the quantum dot layer 30 and the cap layer 36 grown by the semiconductor device manufacturing method according to the fifth embodiment is repeatedly formed. The interval between the repetitively formed quantum dot layers 30 is, for example, 30 nm. The quantum dots 32 of each quantum dot layer 30 have a density of, for example, 5 × 10 ¹⁰ cm ⁻² or more, specifically 7 × 10 ¹⁰ cm ⁻² . Furthermore, the emission wavelength is a long wavelength of, for example, 1.3 μm or more.

An upper cladding layer 58 made of p-Al _0.3 Ga _0.7 As is formed on the active layer 56. The concentration of the p-type impurity introduced into the upper cladding layer 58 is 5 × 10 ¹⁷ cm ⁻³ . The film thickness of the upper cladding layer 58 is 3 μm, for example.

A contact layer 60 made of p-GaAs is formed on the upper cladding layer 58. The concentration of the p-type impurity introduced into the contact layer 60 is, for example, 1 × 10 ¹⁹ cm ⁻³ . The film thickness of the contact layer 60 is, for example, 0.5 μm.

  The contact layer 60 and the upper clad layer 58 are processed into a stripe shape having a width of 3 μm, for example, and a ridge structure that stabilizes the transverse mode of the laser is formed.

  A p-side electrode 62 is formed on the contact layer 60.

  An n-side electrode 64 is formed on the back surface of the n-GaAs substrate 50.

  Thus, the semiconductor device according to the present embodiment is constituted.

The semiconductor device according to the present embodiment has three quantum dot layers 30 grown on the active layer 56 by the semiconductor device manufacturing method according to the fifth embodiment. The quantum dots 32 of each quantum dot layer 30 have a density of, for example, 5 × 10 ¹⁰ cm ⁻² or more, specifically 7 × 10 ¹⁰ cm ⁻² . Therefore, for example, high-speed direct modulation of 10 Gbps can be realized.

  Next, the method for fabricating the semiconductor device according to the present embodiment will be explained with reference to FIGS.

First, a buffer layer 52 made of n-GaAs having an impurity concentration of 1 × 10 ¹⁸ cm ⁻³ is grown on the n-GaAs substrate 50 by, eg, MOCVD. The concentration of the n-type impurity introduced into the n-GaAs substrate 50 is, for example, 1 × 10 ¹⁸ cm ⁻³ . The concentration of the n-type impurity introduced into the buffer layer 52 is, for example, 1 × 10 ¹⁸ cm ⁻³ .

Next, a lower clad layer 54 made of n-Al _0.3 Ga _0.7 As is grown on the buffer layer 52 by, eg, MOCVD (FIG. 20A). The concentration of the n-type impurity introduced into the lower cladding layer 54 is, for example, 5 × 10 ¹⁷ cm ⁻³ . The film thickness of the lower clad layer 54 is 3 μm, for example.

  Next, the laminated film of the quantum dot layer 30 and the cap layer 36 is repeatedly formed on the lower clad layer 54 by the semiconductor device manufacturing method according to the fifth embodiment.

  Here, Sb is deposited on the surface of the cap layer 36 of the first layer that becomes the base layer of the quantum dot layer 30 of the second layer, and the GaSb layer 42 is formed. Therefore, the step of irradiating the surface of the first cap layer 36 with TMSb before the growth of the second quantum dot layer 30 may be omitted. Alternatively, after removing the GaSb layer 42 formed on the surface of the first cap layer 36, the surface of the GaSb layer 42 is irradiated with TMSb, and then the second quantum dot layer 30 may be grown. .

  Similarly, Sb is deposited on the surface of the second cap layer 36 which is the base layer of the third quantum dot layer 30, thereby forming the GaSb layer 42. Therefore, the step of irradiating the surface of the second cap layer 36 with TMSb before the growth of the third quantum dot layer 30 may be omitted. Alternatively, after removing the GaSb layer 42 formed on the surface of the cap layer 36 of the second layer and then irradiating the surface with TMSb, the quantum dot layer 30 of the third layer may be grown. .

  Thus, on the lower clad layer 54, the active layer 54 in which the laminated film of the quantum dot layer 30 and the cap layer 36 grown by the method of manufacturing a semiconductor device according to the fifth embodiment is repeatedly formed is formed (FIG. 20 (b)). The film thickness of the active layer 54 is, for example, 0.5 μm. In addition, by appropriately setting the film thickness of the cap layer 36, the interval between the quantum dot layers 30 is set to, for example, 30 nm.

Next, an upper clad layer 58 made of p-Al _0.3 Ga _0.7 As is grown on the active layer 56 by, eg, MOCVD. The concentration of the p-type impurity introduced into the upper cladding layer 58 is, for example, 5 × 10 ¹⁷ cm ⁻³ . The film thickness of the upper cladding layer 58 is 3 μm, for example.

Next, a contact layer 60 made of p-GaAs is grown on the upper cladding layer 58 by, eg, MOCVD (FIG. 20C). The concentration of the p-type impurity introduced into the contact layer 60 is, for example, 1 × 10 ¹⁹ cm ⁻³ . The film thickness of the contact layer 60 is, for example, 0.5 μm.

  Next, the contact layer 60 and the upper clad layer 58 are processed into a stripe shape having a width of 3 μm, for example, so that the upper clad layer 58 remains on the active layer 56 by about 100 nm (FIG. 21A).

  Next, a p-side electrode 62 is formed on the contact layer 60, and an n-side electrode 64 is formed on the back surface of the GaAs substrate 50 (FIG. 21B).

Thus, the semiconductor device according to the present embodiment is manufactured.
As described above, according to the present embodiment, the quantum dots 32 grown by the semiconductor device manufacturing method according to the fifth embodiment are applied to the active layer 56, so that a quantum dot laser capable of realizing high-speed direct modulation is provided. can do.

[Seventh Embodiment]
A semiconductor device and a manufacturing method thereof according to the seventh embodiment of the present invention will be described with reference to FIGS. FIG. 22 is a schematic view showing the structure of the semiconductor device according to the present embodiment. FIGS. 23, 24, 26 and 29 are process cross-sectional views showing the method for manufacturing the semiconductor device according to the present embodiment. FIG. 27 and FIG. 28 are graphs showing the lower limit value and the upper limit value of the V / III ratio during the growth of each quantum dot layer when growing a plurality of quantum dot layers in the semiconductor device manufacturing method. It is a graph which shows the relationship between temperature and the root mean square roughness of the surface of an upper clad layer, and the relationship between the annealing temperature of a quantum dot layer, and the blue shift of light emission of a quantum dot. Note that the description of the same components as those of the semiconductor device manufacturing method according to the fifth embodiment is omitted or simplified.

  In this embodiment, as in the sixth embodiment, a ridge type quantum dot laser in which quantum dots 32 grown by the semiconductor device manufacturing method according to the fifth embodiment are applied to an active layer of a semiconductor laser will be described.

  First, the structure of the semiconductor device according to the present embodiment will be explained with reference to FIG. FIG. 22A is a sectional view showing the structure of the semiconductor device according to the present embodiment, and FIG. 22B is an enlarged sectional view showing an active layer in the semiconductor device according to the present embodiment.

As shown in FIG. 22A, an n-type lower cladding layer 68 made of n-AlGaAs is formed on an n-GaAs substrate 66. The concentration of the n-type impurity introduced into the n-GaAs substrate 66 is, for example, 1 × 10 ¹⁸ cm ⁻³ . The composition of the lower cladding layer 68 is, for example, Al _0.35 Ga _0.65 As. The concentration of the n-type impurity introduced into the lower cladding layer 68 is, for example, 5 × 10 ¹⁷ cm ⁻³ . The film thickness of the lower cladding layer 68 is, for example, 1 to 3 μm. The lower cladding layer 68 may be formed on the n-GaAs substrate 66 through a buffer layer made of n-GaAs, as in the semiconductor device according to the sixth embodiment.

  An SCH (Separate Confinement Heterostructure) layer 70 made of GaAs is formed on the lower clad layer 68. The film thickness of the SCH layer 70 is 40 nm, for example.

  An active layer 72 is formed on the SCH layer 70. As shown in FIG. 22B, the active layer 72 includes a plurality of stacked films of a quantum dot layer 30 made of InAs and a cap layer 36 made of GaAs grown by the semiconductor device manufacturing method according to the fifth embodiment. For example, 5 to 10 layers are repeatedly formed. The cap layer 36 functions as a barrier layer. A barrier layer 71 made of GaAs is formed between the first quantum dot layer 30 and the SCH layer 70. The film thicknesses of the barrier layer 71 and the cap layer 36 are each 40 nm, for example. In FIG. 22B, the GaSb layer 42 (see FIG. 18C) is omitted.

Note that a stress relaxation layer made of InGaAs may be formed between the quantum dot layer 30 and the cap layer 36 to cover the quantum dot layer 30 including the quantum dots 32. In this case, the composition of the stress relaxation layer is, for example, In _0.1 Ga _0.9 As.

  In this embodiment, when the quantum dot layer 30 made of InAs of n layers (n is an integer of 2 or more) is grown by MOCVD, the i-th layer (i is an integer satisfying 1 ≦ i ≦ n−1). The V / III ratio during the growth of the (i + 1) th quantum dot layer 30 is set higher than the V / III ratio during the growth of the quantum dot layer 30. As a result, a plurality of quantum dot layers 30 are repeatedly formed in a state in which the size distribution and density of the quantum dots 32 are kept uniform between the layers without causing defects. This point will be described later.

  On the active layer 72, as shown in FIG. 22A, an SCH layer 74 made of GaAs is formed. The film thickness of the SCH layer 74 is 40 nm, for example.

On the SCH layer 74, a p-type upper cladding layer 76 made of p-AlGaAs is formed. The composition of the upper cladding layer 76 is, for example, Al _0.35 Ga _0.65 As. The concentration of the p-type impurity introduced into the upper cladding layer 76 is, for example, 5 × 10 ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ . The film thickness of the upper cladding layer 76 is, for example, 1 to 3 μm.

A contact layer 78 made of p-GaAs is formed on the upper cladding layer 76. The concentration of the p-type impurity introduced into the contact layer 78 is, for example, 1 × 10 ¹⁹ cm ⁻³ . The thickness of the contact layer 78 is, for example, 0.5 μm.

  The contact layer 78 and the upper cladding layer 76 are processed, for example, in a stripe shape having a width of 3 μm, and a ridge structure that stabilizes the transverse mode of the laser is formed.

  A p-side electrode 80 is formed on the contact layer 78.

  An n-side electrode 82 is formed on the back surface of the n-GaAs substrate 66.

  Thus, the semiconductor device according to the present embodiment is constituted.

  Next, the method for fabricating the semiconductor device according to the present embodiment will be explained with reference to FIGS.

First, an n-type lower cladding layer 68 made of n-AlGaAs is grown on the n-GaAs substrate 66 by MOCVD (FIG. 23A). The concentration of the n-type impurity introduced into the n-GaAs substrate 66 is, for example, 1 × 10 ¹⁸ cm ⁻³ . The composition of the lower cladding layer 68 is, for example, Al _0.35 Ga _0.65 As. The concentration of the n-type impurity introduced into the lower cladding layer 68 is, for example, 5 × 10 ¹⁷ cm ⁻³ . The film thickness of the lower cladding layer 68 is, for example, 1 to 3 μm. In addition, TMG is used as a Ga raw material when the lower cladding layer 68 is grown.

  Next, an SCH layer 70 made of GaAs is grown on the lower clad layer 54 by MOCVD (FIG. 23B). The film thickness of the SCH layer 70 is 40 nm, for example.

  Next, a multilayer film of the quantum dot layer 30 and the cap layer 36 is repeatedly formed on the SCH layer 70 by the semiconductor device manufacturing method according to the fifth embodiment, for example, 5 to 10 layers. Thereby, an active layer 72 including a plurality of quantum dot layers 30 is formed (FIG. 23C).

  Here, a method for forming the active layer 72 will be described in detail with reference to FIGS.

  First, a barrier layer 71 made of GaAs is grown on the SCH layer 70 by MOCVD (FIG. 24A). The film thickness of the barrier layer 71 is, for example, 40 nm.

  Next, a multilayer film of the quantum dot layer 30 and the cap layer 36 functioning as a barrier layer is repeatedly formed by a semiconductor device manufacturing method according to the fifth embodiment, for example, 5 to 10 layers. The film thickness of the cap layer 36, that is, the interval between the quantum dot layers 30 is, for example, 40 nm.

In addition, after growing each quantum dot layer 30, before growing the cap layer 36, you may form the stress relaxation layer which consists of InGaAs which covers the quantum dot layer 30 containing the quantum dot 32. FIG. In this case, the composition of the stress relaxation layer is, for example, In _0.1 Ga _0.9 As.

  In this embodiment, when the quantum dot layer 30 made of InAs of n layers (n is an integer of 2 or more) is grown by MOCVD, the i-th layer (i is an integer satisfying 1 ≦ i ≦ n−1). The V / III ratio during the growth of the (i + 1) th quantum dot layer 30 is set higher than the V / III ratio during the growth of the quantum dot layer 30. Thus, as the number of quantum dot layers 30 increases, the V / III ratio during growth of the quantum dot layers 30 is gradually increased. Here, the V / III ratio during the growth of the quantum dot layer 30 is the ratio of the supply amount of the V group material to the supply amount of the group III material supplied into the reaction chamber of the MOCVD apparatus when the quantum dot layer 30 is grown. In the present embodiment, it refers to the ratio of the supply amount of TBA to the supply amount of TMI.

  Thus, when setting the V / III ratio at the time of growth of the quantum dot layer 30, the V / III ratio at the time of growth of each quantum dot layer 30 is set within the range shown in FIG. FIG. 25 is a graph showing a lower limit value and an upper limit value of the V / III ratio during growth of each quantum dot layer 30 when growing a plurality of quantum dot layers 30 in the semiconductor device manufacturing method according to the present embodiment. . The vertical axis of the graph represents the V / III ratio, and the horizontal axis represents the layer number of the quantum dot layer 30, that is, the number of the quantum dot layer 30. In the graph, ♦ indicates the lower limit of the V / III ratio, and ■ indicates the upper limit of the V / III ratio.

  As shown in FIG. 25, the V / III ratio during the growth of the first quantum dot layer 30 is set to 0.1 to 0.8.

  The V / III ratio during the growth of the quantum dot layer 30 during the growth of the second quantum dot layer 30 is set to 1.3 to 3.6.

  The V / III ratio during the growth of the third quantum dot layer 30 is set to 1.8 to 4.0.

  In addition, the V / III ratio during the growth of the fourth and subsequent quantum dot layers 30 is set to 1.8 to 4.0.

  In the method of manufacturing the semiconductor device according to the present embodiment, when the quantum dot layer 30 made of InAs of n layers (n is an integer of 2 or more) is grown by MOCVD, the i-th layer (i is 1 ≦ i ≦ n). -1), the V / III ratio during the growth of the (i + 1) th quantum dot layer 30 is set higher than the V / III ratio during the growth of the quantum dot layer 30 and the quantum dot layer 30 layer One of the main characteristics is that the V / III ratio during the growth of the quantum dot layer 30 is gradually increased as the number increases.

  By setting the V / III ratio during the growth of the quantum dot layer 30 in this manner, the size distribution and density of the quantum dots 32 are kept uniform between the layers without causing defects, and a plurality of quantum dot layers 30 are formed. Can be formed repeatedly.

  Note that the lower limit value and the upper limit value of the V / III ratio during growth of the quantum dot layer 30 shown in FIG. 25 have an important significance in repeatedly forming a plurality of quantum dot layers 30 as described below. Have.

  First, when the V / III ratio at the time of growth of a certain quantum dot layer 30 falls below the lower limit value, the quantum dots 32 included in the quantum dot layer 30 increase in density but rapidly expand in size distribution. The average size decreases rapidly. As a result, the characteristics of the quantum dots 32 included in the quantum dot layer 30 are significantly different from the characteristics of the quantum dots 32 included in the lower quantum dot layer 30, particularly the first quantum dot layer 30. The quantum dots used in the quantum dot laser are required to have a size sufficient to realize a uniform size distribution and an emission wavelength of 1.3 μm. For this reason, the quantum dots 32 grown at a V / III ratio lower than the lower limit are not suitable for quantum dot lasers.

  Further, when the V / III ratio at the time of growth of a certain quantum dot layer 30 exceeds the upper limit value, the density of the combined islands in the quantum dot layer 30 increases rapidly. These huge islands are plastically relaxed and have dislocations. For this reason, non-radiative recombination centers are introduced into the quantum dot layer 30 and its optical characteristics are greatly degraded. In addition, the huge islands hinder the repeated formation of the plurality of quantum dot layers 30.

  In the present embodiment, the V / III ratio during growth of each quantum dot layer 30 is set within the range of the lower limit value and the upper limit value shown in FIG. 25, so that the quantum dot layer including the quantum dots 32 suitable for the quantum dot laser 30 can be formed by repeating a plurality of layers.

  After forming an active layer 72 in which a plurality of quantum dot layers 30 are repeatedly formed in this way, an SCH layer 74 made of GaAs is grown on the active layer 72 by MOCVD (FIG. 26A). The film thickness of the SCH layer 74 is 40 nm, for example.

Next, a p-type upper cladding layer 76 made of p-AlGaAs is grown on the SCH layer 74 by MOCVD. The composition of the upper cladding layer 76 is, for example, Al _0.35 Ga _0.65 As. The concentration of the p-type impurity introduced into the upper cladding layer 76 is, for example, 5 × 10 ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ . The film thickness of the upper cladding layer 76 is, for example, 1 to 3 μm. The growth condition of the upper cladding layer 76 is that the substrate temperature, that is, the growth temperature is 610 to 660 ° C. The source gas supplied into the reaction chamber of the MOCVD apparatus is TMA (trimethylaluminum) as the Al source and TMG as the Ga source TBA is used as the As raw material.

  As described above, the manufacturing method of the semiconductor device according to the present embodiment is also mainly characterized in that the growth temperature is set to 610 to 660 ° C., and TMG is supplied as the Ga material into the reaction chamber of the MOCVD apparatus to grow the upper cladding layer 76. There is one.

  Here, the relationship between the growth temperature of the upper cladding layer 76, the root mean square roughness of the surface of the upper cladding layer 76, and the blue shift of light emission of the quantum dots 32 will be described with reference to FIGS.

FIG. 27 is a graph showing the relationship between the growth temperature of the upper cladding layer made of AlGaAs and the mean square roughness of the surface of the upper cladding layer, and the relationship between the annealing temperature of the quantum dot layer and the blue shift of light emission of the quantum dots. FIG. 27 shows a case where the stress relaxation layer made of In _0.1 Ga _0.9 As covering the quantum dot layer including the quantum dots is not formed. The film thickness of the cap layer is 40 nm, and five quantum dot layers are formed repeatedly according to the present invention. The peak emission wavelength in the ground state of the quantum dot is 1.28 μm. The vertical axis on the right side of the graph represents the root mean square roughness of the surface of the upper cladding layer, the vertical axis on the left side represents the blue shift of emission of the quantum dots, and the horizontal axis of the graph represents the growth of the upper cladding layer with respect to the mean square roughness. The temperature indicates the annealing temperature of the quantum dot layer with respect to the blue shift of light emission. In the graph, ■ indicates the mean square roughness of the surface of the upper cladding layer, and ◆ indicates the blue shift of light emission of the quantum dots.

  The quality of the surface morphology of the crystal constituting the quantum dot laser is one of the extremely important factors that influence the performance of the laser. That is, it is desirable that the crystal surface be as flat as possible. The quality of this crystal form is dramatically improved by increasing the crystal growth temperature.

  As shown in FIG. 27, when an upper cladding layer made of AlGaAs having a film thickness of 1.0 to 1.4 μm is formed at a growth temperature of 600 ° C. or lower, the surface of the upper cladding layer has a root mean square roughness exceeding 5 nm. It is very rough.

  On the other hand, when the growth temperature is 610 ° C., the roughness of the surface of the upper cladding layer is dramatically improved, and the root mean square roughness is about 2 nm. Further, when the growth temperature is 620 ° C. or higher, the surface of the upper cladding layer is flat with a mean square roughness of 0.4 nm or less. When the growth temperature is 640 ° C. or higher, the mean square roughness is very flat with a thickness of about 0.2 nm.

  In the present embodiment, since the upper cladding layer 76 is grown at a growth temperature of 610 ° C. or higher, it is possible to grow the upper cladding layer 76 with high crystal quality and flatness. Thereby, the roughness of the interface between the SCH layer 74 and the upper clad layer 76 and the roughness of the interface between the upper clad layer 76 and the contact layer 78 grown in a subsequent process can be reduced. Thereby, the scattering loss of the light in a quantum dot laser can be reduced.

  In addition, as described below, in this embodiment, even when the upper cladding layer 76 is grown at such a relatively high growth temperature, the quantum dots 32 are destroyed or the light emission characteristics of the quantum dots 32 are deteriorated. I don't have to.

  During the growth of the upper cladding layer, the active layer including the quantum dots is annealed to a very high temperature.

  In the case of a conventional growth method in which a quantum dot made of InAs and a cap layer made of GaAs are grown without using Sb, if the quantum dot is annealed to a very high temperature, the emission wavelength of the quantum dot becomes shorter. Shift, that is, blue shift. Furthermore, quantum dots may be destroyed.

  On the other hand, in the case of the present invention in which a quantum dot made of InAs and a cap layer made of GaAs are grown using Sb, it is hardly affected by annealing, and the quantum dot is annealed to a very high temperature. However, the emission wavelength of the quantum dots does not blue shift, and the quantum dots are not destroyed.

  In FIG. 27, the quantum dots according to the present invention in the case where the annealing process is performed for a processing time of 30 minutes corresponding to the case where the upper cladding layer made of AlGaAs having a thickness of 1.4 μm is grown at a growth rate of about 0.8 nm / s. The blue shift of the light emission is shown. Here, the blue shift of light emission of the quantum dots means the difference in peak of the light emission wavelength of the quantum dots before and after the annealing treatment. A light emission blue shift value of 0 means that there is no change in the peak emission wavelength of the quantum dots before and after annealing. A negative value means that the peak emission wavelength of the quantum dot is blue-shifted, and the larger the absolute value is, the larger the shift amount is.

  From FIG. 27, it can be seen that the peak emission wavelength of the quantum dots is not blue shifted up to the annealing temperature of 660 ° C. In contrast, at an annealing temperature of 670 ° C. or higher, the peak emission wavelength of the quantum dots is blue shifted by 70 nm or more.

  In the present embodiment, since the upper cladding layer 76 is grown at a growth temperature of 660 ° C. or lower, the peak emission wavelength of the quantum dots 32 included in the active layer 72 does not blue shift during the growth of the upper cladding layer 76.

  Thus, in this embodiment, since the upper cladding layer 76 made of AlGaAs is grown at a growth temperature of 610 to 660 ° C., the crystal quality can be reduced without causing deterioration of the light emission characteristics of the quantum dots 32 or destruction of the quantum dots 32. A high and flat upper cladding layer 76 can be grown.

  It has been found that the blue shift of light emission of the quantum dots depends on the coating state of the quantum dots.

FIG. 28 shows the annealing temperature of the quantum dot layer and the light emission of the quantum dots in the case where the stress relaxation layer made of In _0.1 Ga _0.9 As covering the quantum dot layer including the quantum dots is formed. Shows the relationship with the blue shift. The stacked structure of the quantum dot layer in the case shown in FIG. 28 is the same as that shown in FIG. 27 except that a stress relaxation layer is formed. In this case, the peak emission wavelength in the ground state of the quantum dots is 1.305 μm.

  From FIG. 28, it can be seen that when the stress relaxation layer is formed, the peak emission wavelength of the quantum dots is not blue shifted up to the annealing temperature of 640 ° C. In contrast, at an annealing temperature of 650 ° C. or higher, it can be seen that the peak emission wavelength of the quantum dots is blue-shifted by 70 nm or more.

  Therefore, when the stress relaxation layer covering the quantum dot layer 30 including the quantum dots 32 is formed, it is desirable to set the growth temperature of the upper cladding layer 76 to 610 to 640 ° C.

After growing the upper cladding layer 76 in this way, a contact layer 78 made of p-GaAs is grown on the upper cladding layer 76 by MOCVD (FIG. 26C). The concentration of the p-type impurity introduced into the contact layer 78 is, for example, 1 × 10 ¹⁹ cm ⁻³ . The film thickness of the contact layer 78 is 0.5 μm, for example. The growth condition of the contact layer 78 is that the growth temperature is lowered from the growth temperature of the upper cladding layer 76 to 600 to 610 ° C., and the source gas supplied into the reaction chamber of the MOCVD apparatus includes Ga cladding material as the upper cladding layer 76. Instead of TMG used during the growth, TEG is used, and TBA is used as the As raw material.

  As described above, in the method of manufacturing the semiconductor device according to the present embodiment, the growth temperature is lowered from the growth temperature of the upper cladding layer 76 to 600 to 610 ° C., and instead of TMG used for the growth of the upper cladding layer 76 as a Ga material. One of the main characteristics is that the contact layer 78 is grown by supplying TEG into the reaction chamber of the MOCVD apparatus.

  By growing the contact layer 78 under such growth conditions, the contact layer 78 with high crystal quality can be grown, and the roughness of the interface between the upper cladding layer 76 and the contact layer 78 can be further reduced. . Thereby, the light scattering loss in the quantum dot laser can be further reduced. In addition, leakage current in the quantum dot laser can be reduced.

  Further, since the contact layer 78 is grown at a growth temperature of 600 to 610 ° C., the light emission characteristics of the quantum dots 32 are not deteriorated when the contact layer 78 is grown. Further, the quantum dots 32 are not destroyed.

  Next, the contact layer 78 and the upper clad layer 76 are processed into a stripe shape having a width of 3 μm, for example, so that the upper clad layer 76 remains about 10 to 100 nm on the SCH layer 74 (FIG. 29A).

  Next, the p-side electrode 80 is formed on the contact layer 78, and the n-side electrode 82 is formed on the back surface of the GaAs substrate 62 (FIG. 29B).

  Thus, the semiconductor device according to the present embodiment is manufactured.

  Thus, according to this embodiment, when growing the quantum dot layer 30 made of n-layer InAs by the MOCVD method, the V / III ratio during the growth of the i-th quantum dot layer 30 is larger than The V / III ratio during growth of the (i + 1) th quantum dot layer 30 is set high, and the V / III ratio during growth of the quantum dot layer 30 is gradually increased as the number of quantum dot layers 30 increases. Therefore, a plurality of quantum dot layers 30 can be repeatedly formed while keeping the size distribution and density of the quantum dots 32 uniform between the layers without causing defects.

  In addition, according to the present embodiment, the growth temperature is set to 610 to 660 ° C., and TMG is supplied as a Ga raw material into the reaction chamber of the MOCVD apparatus to grow the upper clad layer 76. The flat upper cladding layer 76 with high crystal quality can be grown without breaking the quantum dots 32. Thereby, the roughness of the interface between the SCH layer 74 and the upper cladding layer 76 and the roughness of the interface between the upper cladding layer 76 and the contact layer 78 can be reduced. Thereby, the scattering loss of light can be reduced in the quantum dot laser.

  Furthermore, according to the present embodiment, the growth temperature is lowered from the growth temperature of the upper cladding layer 76 to 600 to 610 ° C., and TEG is used as a Ga raw material instead of TMG used during the growth of the upper cladding layer 76 in the MOCVD apparatus. Since the contact layer 78 is grown by being supplied into the reaction chamber, the contact layer 78 with high crystal quality can be grown without deteriorating the light emission characteristics of the quantum dots 32 or destroying the quantum dots 32. Therefore, the roughness of the interface between the upper cladding layer 76 and the contact layer 78 can be further reduced. Thereby, the leakage current in the quantum dot laser can be reduced.

  In the above description, the case where the multilayer film of the quantum dot layer 30 and the cap layer 36 is repeatedly formed by the semiconductor device manufacturing method according to the fifth embodiment has been described. However, the semiconductor according to the first to fourth embodiments is described. A laminated film of the quantum dot layer 30 and the cap layer 36 may be repeatedly formed by any one of the device manufacturing methods. In this case as well, the V / III ratio during growth of the quantum dot layer 30 is set in the same manner as described above, and the V / III ratio during growth of the quantum dot layer 30 is gradually increased as the number of quantum dot layers 30 increases. By increasing the height, the quantum dot layer 30 having a plurality of layers can be repeatedly formed while keeping the size distribution and density of the quantum dots 32 uniform between the layers without causing defects.

  In the above description, a case where a stacked film of the quantum dot layer 30 and the cap layer 36 is repeatedly formed has been described. However, the quantum dot layer can be formed by any of the semiconductor device manufacturing methods according to the first to fifth embodiments. Only one laminated film of the cap 30 and the cap layer 36 may be formed. Even in this case, the upper clad layer 76 is grown under the same growth conditions as described above, so that the upper clad layer having a high crystal quality and a flatness is obtained without causing deterioration of the light emission characteristics of the quantum dots 32 or destruction of the quantum dots 32. 76 can grow. In addition, by growing the contact layer 78 under the same growth conditions as described above, the contact layer 78 with high crystal quality can be grown without deteriorating the light emission characteristics of the quantum dots 32 or destroying the quantum dots 32. .

[Eighth Embodiment]
A method for manufacturing a semiconductor device according to the eighth embodiment of the present invention will be described with reference to FIGS. FIG. 30 is a process sectional view showing the method for manufacturing the semiconductor device according to the present embodiment. Note that the description of the same components as those of the semiconductor device and the manufacturing method thereof according to the seventh embodiment is omitted or simplified.

  The semiconductor device manufacturing method according to the present embodiment is substantially the same as the semiconductor device manufacturing method according to the seventh embodiment. In the method of manufacturing the semiconductor device according to the present embodiment, when the upper clad layer 76 is grown, the V / III ratio during the growth of the upper clad layer 76 is controlled without using a dopant. It is characterized by controlling the mold carrier concentration.

  First, in the same manner as in the semiconductor device manufacturing method according to the seventh embodiment, the layers up to the SCH layer 74 are formed on the n-GaAs substrate 66 (FIG. 30A).

Next, a p-type upper cladding layer 76 made of p-AlGaAs is grown on the SCH layer 74 by MOCVD (FIG. 30B). The composition of the upper cladding layer 76 is, for example, Al _0.35 Ga _0.65 As. The film thickness of the upper cladding layer 76 is, for example, 1 to 3 μm. The growth condition of the upper cladding layer 76 is that the growth temperature is 610 to 660 ° C. The source gas supplied into the reaction chamber of the MOCVD apparatus is TMA as the Al source, TMG as the Ga source, and TBA as the As source. Use.

  In the present embodiment, the V / III ratio during the growth of the upper cladding layer 76 is controlled without supplying a dopant for controlling the p-type carrier concentration during the growth of the upper cladding layer 76 into the reaction chamber of the MOCVD apparatus. Thus, the p-type carrier concentration of the upper cladding layer 76 is controlled. Here, the V / III ratio during the growth of the upper cladding layer 76 is the ratio of the supply amount of the group V material to the supply amount of the group III material supplied into the reaction chamber of the MOCVD apparatus when the upper cladding layer 76 is grown. In the present embodiment, the ratio of the supply amount of TBA to the supply amount of TMA and TMG.

  The p-type carrier concentration of the upper cladding layer 76 decreases as the V / III ratio during the growth of the upper cladding layer 76 increases, and increases as the V / III ratio decreases. Specifically, the p-type carrier concentration of the upper cladding layer 76 decreases as the partial pressure of TBA, which is a group V raw material in the reaction chamber of the MOCVD apparatus, grows when the upper cladding layer 76 is grown. Increases as decreases.

In this embodiment, based on the relationship between the V / III ratio and the p-type carrier concentration, the upper clad is controlled by controlling the V / III ratio during the growth of the upper clad layer 76 within a range of 1 to 10, for example. The p-type carrier concentration of the layer 76 is controlled to a range of, for example, 10 ¹⁷ to 10 ¹⁸ cm ⁻³ . Note that the p-type carrier concentration of the upper cladding layer 76 depends on the growth temperature in addition to the V / III ratio, so the V / III ratio is appropriately set according to the growth temperature.

  When the growth temperature of the upper cladding layer 76 is 610 to 660 ° C., specifically, the V / III ratio is set as follows.

For example, when the p-type carrier concentration of the upper cladding layer 76 is set to 6 × 10 ¹⁷ cm ⁻³ , the V / III ratio during the growth of the upper cladding layer 76 is set to 5-8.

For example, when the p-type carrier concentration of the upper cladding layer 76 is set to 1.0 × 10 ¹⁸ cm ⁻³ , the V / III ratio during the growth of the upper cladding layer 76 is set to 3-6.

  As described above, in the method of manufacturing the semiconductor device according to the present embodiment, the p-type carrier concentration of the upper cladding layer 76 is controlled by controlling the V / III ratio during the growth of the upper cladding layer 76 without using a dopant. Therefore, the p-type carrier concentration of the upper cladding layer 76 can be easily set to a desired concentration.

  The V / III ratio during the growth of the upper cladding layer 76 is desirably controlled so as to decrease from the active layer 72 side to the contact layer 78 side of the upper cladding layer 76. That is, it is desirable to control the V / III ratio of the portion of the upper clad layer 76 on the active layer 72 side to be higher than the V / III ratio of other portions.

  Since the process after growing the upper cladding layer 76 is the same as that of the semiconductor device manufacturing method according to the seventh embodiment, the description thereof is omitted.

  Thus, according to the present embodiment, the p-type carrier concentration of the upper cladding layer 76 is controlled by controlling the V / III ratio during the growth of the upper cladding layer 76 without using a dopant. The p-type carrier concentration of the cladding layer 76 can be easily set to a desired concentration.

[Modified Embodiment]
The present invention is not limited to the above embodiment, and various modifications can be made.

  For example, although the case where an InAs layer is grown as the quantum dot layer 30 has been described in the above embodiment, the material of the quantum dot layer 30 is not limited to this. As a material of the quantum dot layer 30, a material having a lattice constant different from that of the buffer layer 28 can be used as appropriate, and for example, other group III-V semiconductors can be used.

  Moreover, although the case where the GaAs layer was grown as the cap layer 36 was demonstrated in the said embodiment, the material of the cap layer 36 is not limited to this. As a material of the cap layer 36, InGaAs or the like can be used.

  Moreover, although the said embodiment demonstrated the case where the semiconductor layer was grown by MOCVD method, the growth method of a semiconductor layer is not limited to this. For example, the semiconductor layer may be grown by molecular beam epitaxy (MBE) or the like.

  Moreover, although the said embodiment demonstrated the case where the surface of the quantum dot layer 30 was irradiated with TMSb as organic Sb raw material gas, the organic Sb raw material used for Sb irradiation is not limited to this. For example, in addition to TMSb, Sb irradiation may be performed by irradiating the surface of the quantum dot layer 30 with an organic Sb source gas such as TESb.

  Moreover, although the said embodiment demonstrated the case where TMSb and TEG were irradiated to the surface of the quantum dot layer 30 simultaneously, the organometallic raw material used for irradiation of GaSb is not limited to these. For example, irradiation with GaSb may be performed by simultaneously irradiating the organic Sb source gas described above and an organic Ga source gas such as TMGa in addition to TEG. Moreover, you may irradiate simultaneously organic Sb source gas and organic source gas of III group metals (In, Al) other than Ga.

  Moreover, although the said embodiment demonstrated the case where TMSb was irradiated to the surface of the buffer layer 28 before growing the quantum dot layer 30, irradiation of Sb is not limited to this. In addition to TMSb, Sb irradiation may be performed by irradiating the surface of the buffer layer 28 with the organic Sb source gas.

  In the above embodiment, the case where the surface of the buffer layer 28 is irradiated with Sb before the quantum dot layer 30 is grown has been described. However, the surface of the buffer layer 28 is irradiated with Sb during the growth of the quantum dot layer 30. May be. Further, the surface of the buffer layer 28 may be irradiated with GaSb before or during the growth of the quantum dot layer 30. The irradiation with GaSb can be performed by simultaneously irradiating the surface of the buffer layer 28 with the organic Sb source gas and the organic Ga source gas.

Moreover, although the said embodiment demonstrated the case where TBA was irradiated to the surface of the quantum dot layer 30 for a fixed time, and the surface of the quantum dot layer 30 was etched with TBA, As is irradiated to the surface of the quantum dot layer 30 for a fixed time. The raw material is not limited to this. For example, in addition to TBA, AsH ₃ , As ₂ , As _{4 and the} like can be used.

  In the above embodiment, the case where the InSb layer 46 is removed by irradiating the surface of the quantum dot layer 30 with TBA for a certain time has been described. However, by etching the surface of the quantum dot layer 30 by other methods. The InSb layer 46 may be removed.

  In the sixth to eighth embodiments, the case where AlGaAs is used as the material of the lower cladding layers 54 and 68 and the upper cladding layers 60 and 76 is described. However, the material of the lower cladding layer and the upper cladding layer is limited to this. For example, other group III-V compound semiconductors may be used.

  In the sixth to eighth embodiments, the case where GaAs is used as the material of the contact layers 60 and 78 has been described. However, the material of the contact layer is not limited to this, for example, other III-V group A compound semiconductor may be used.

  In the seventh and eighth embodiments, the case where the SCH layers 70 and 74 are formed has been described. However, these may not necessarily be formed. In the case where the SCH layer 74 is not formed, the roughness of the interface between the active layer 72 and the upper cladding layer 76 can be reduced by growing the upper cladding layer 76 under the growth conditions described above.

  In the sixth to eighth embodiments, the case where the present invention is applied to a quantum dot laser including a quantum dot layer as an active layer has been described. However, the present invention includes a quantum dot optical amplifier, The present invention can be applied to other optical semiconductor devices including a quantum dot layer as an active layer, such as a quantum dot wavelength converter and a quantum dot waveform shaper.

  As detailed above, the characteristics of the present invention are summarized as follows.

(Appendix 1) Forming quantum dots on the underlayer by self-organized growth;
Irradiating the surface of the quantum dots with an organic Sb source gas;
And a step of growing a cap layer on the quantum dots.

(Supplementary Note 2) A step of forming quantum dots on the underlayer by self-organized growth;
Irradiating the surface of the underlayer with Sb or GaSb before the step of forming the quantum dots or during the step of forming the quantum dots;
And a step of growing a cap layer on the quantum dots.

(Additional remark 3) In the manufacturing method of the semiconductor device of Additional remark 2,
The method further includes the step of removing the surface layer containing Sb deposited on the surface of the quantum dots by irradiating the surface of the quantum dots with an As source gas for a predetermined time or etching the surface of the quantum dots. A method for manufacturing a semiconductor device.

(Additional remark 4) In the manufacturing method of the semiconductor device of Additional remark 3,
A method of manufacturing a semiconductor device, further comprising irradiating the surface of the quantum dots with an organic Sb source gas after the step of removing the surface layer and before the step of growing the cap layer.

(Additional remark 5) In the manufacturing method of the semiconductor device of Additional remark 1 or 4,
In the step of irradiating the organic Sb source gas, a group III metal organic source gas is irradiated simultaneously with the organic Sb source gas.

(Appendix 6) In the method for manufacturing a semiconductor device according to any one of appendices 1 to 5,
In the step of growing the cap layer, the cap layer is grown at a growth rate of 0.275 nm / s or less.

(Appendix 7) In the method for manufacturing a semiconductor device according to any one of appendices 1 to 6,
Forming an active layer comprising the quantum dots;
A method of manufacturing a semiconductor device, further comprising: growing a clad layer on the active layer using a trimethyl gallium as a Ga material at a growth temperature of 610 to 660 ° C.

(Appendix 8) In the method for manufacturing a semiconductor device according to Appendix 7,
A step of growing a contact layer on the clad layer using triethylgallium as a Ga material at a growth temperature of 600 to 610 ° C. after the step of growing the clad layer. Production method.

(Supplementary note 9) In the method for manufacturing a semiconductor device according to any one of supplementary notes 1 to 6,
Forming an active layer comprising the quantum dots;
Growing a cladding layer on the active layer;
A method for manufacturing a semiconductor device, further comprising: growing a contact layer on the clad layer at a growth temperature of 600 to 610 ° C. using triethylgallium as a Ga material.

(Additional remark 10) The process of growing the quantum dot layer containing the quantum dot formed by self-organization growth; The process of irradiating the surface of the said quantum dot layer with organic Sb source gas; On the said quantum dot layer, A step of forming an active layer including n layers (n is an integer of 2 or more) of the quantum dot layer on a semiconductor substrate by repeating a step of growing a cap layer,
In the step of forming the active layer, the quantum of the (i + 1) th layer is larger than the V / III ratio during growth of the quantum dot layer of the i-th layer (i is an integer satisfying 1 ≦ i ≦ n−1). A method of manufacturing a semiconductor device, characterized in that the V / III ratio during the growth of the dot layer is set high.

(Supplementary Note 11) A step of growing a quantum dot layer including quantum dots formed by self-organized growth; and before the step of growing the quantum dot layer or during the step of growing the quantum dot layer, the quantum By repeating the step of irradiating the surface of the underlayer of the dot layer with Sb or GaSb; and the step of growing a cap layer on the quantum dot layer, the quantum dot layer is formed on the semiconductor substrate by n layers (n Is a step of forming an active layer including an integer of 2 or more,
In the step of forming the active layer, the quantum of the (i + 1) th layer is larger than the V / III ratio during growth of the quantum dot layer of the i-th layer (i is an integer satisfying 1 ≦ i ≦ n−1). A method of manufacturing a semiconductor device, characterized in that the V / III ratio during the growth of the dot layer is set high.

(Additional remark 12) In the manufacturing method of the semiconductor device of Additional remark 11,
The method further includes the step of removing the surface layer containing Sb deposited on the surface of the quantum dots by irradiating the surface of the quantum dots with an As source gas for a predetermined time or etching the surface of the quantum dots. A method for manufacturing a semiconductor device.

(Additional remark 13) In the manufacturing method of the semiconductor device of Additional remark 12,
After the step of removing the surface layer and before the step of growing the cap layer, the method further includes the step of irradiating the surface of the quantum dot layer with an organic Sb source gas. .

(Additional remark 14) In the manufacturing method of the semiconductor device of Additional remark 10 or 13,
In the step of irradiating the organic Sb source gas, a group III metal organic source gas is irradiated simultaneously with the organic Sb source gas.

(Supplementary note 15) In the method for manufacturing a semiconductor device according to any one of supplementary notes 10 to 14,
In the step of growing the cap layer, the cap layer is grown at a growth rate of 0.275 nm / s or less.

(Supplementary Note 16) In the method for manufacturing a semiconductor device according to any one of supplementary notes 10 to 15,
A step of growing a clad layer on the active layer using a trimethyl gallium as a Ga raw material at a growth temperature of 610 to 660 ° C. after the step of forming the active layer. Manufacturing method.

(Supplementary Note 17) In the method for manufacturing a semiconductor device according to Supplementary Note 16,
A step of growing a contact layer on the clad layer using triethylgallium as a Ga material at a growth temperature of 600 to 610 ° C. after the step of growing the clad layer. Production method.

(Supplementary note 18) In the method for manufacturing a semiconductor device according to any one of supplementary notes 10 to 15,
After the step of forming the active layer, growing a clad layer on the active layer;
A method for manufacturing a semiconductor device, further comprising: growing a contact layer on the clad layer at a growth temperature of 600 to 610 ° C. using triethylgallium as a Ga material.

(Supplementary note 19) In the method for manufacturing a semiconductor device according to supplementary note 7 or 16,
In the step of growing the cladding layer, the p-type carrier concentration of the cladding layer is controlled by controlling the V / III ratio during the growth of the cladding layer without using a dopant. Manufacturing method.

(Supplementary Note 20) Quantum dots formed on the underlayer by self-organized growth;
A cap layer embedding the quantum dots;
A semiconductor device comprising: a thin film including a group III metal and Sb formed between the quantum dot and the cap layer.

It is a schematic sectional drawing explaining the defect which generate | occur | produces in the growth method of the conventional quantum dot. It is process sectional drawing (the 1) explaining the outline of the manufacturing method of the semiconductor device by this invention. It is process sectional drawing (the 2) explaining the outline of the manufacturing method of the semiconductor device by this invention. It is a schematic sectional drawing which shows the structure of the semiconductor device by this invention. 4 is a graph showing a partial pressure of a source gas supplied in the method for manufacturing a semiconductor device according to the first embodiment of the present invention. It is process sectional drawing which shows the manufacturing method of the semiconductor device by 1st Embodiment of this invention. It is a graph which shows PL emission spectrum at the room temperature of the quantum dot in the case where Sb irradiation is performed after the growth of the quantum dot. It is a graph which shows the partial pressure etc. of the source gas supplied in the manufacturing method of the semiconductor device by 2nd Embodiment of this invention. It is process sectional drawing which shows the manufacturing method of the semiconductor device by 2nd Embodiment of this invention. It is a graph which shows the partial pressure etc. of the source gas supplied in the manufacturing method of the semiconductor device by 3rd Embodiment of this invention. It is process sectional drawing (the 1) which shows the manufacturing method of the semiconductor device by 3rd Embodiment of this invention. It is process sectional drawing (the 2) which shows the manufacturing method of the semiconductor device by 3rd Embodiment of this invention. It is a graph which shows the relationship between the peak emission wavelength and emission intensity of a quantum dot, and the etching time by TBA. It is a graph which shows PL emission spectrum at room temperature of the quantum dot obtained about the sample from which the growth rate of a cap layer differs. It is a schematic sectional drawing explaining the spreading | diffusion of Sb in the manufacturing method of the semiconductor device by 4th Embodiment of this invention. It is a graph which shows the partial pressure etc. of the source gas supplied in the manufacturing method of the semiconductor device by 5th Embodiment of this invention. It is process sectional drawing (the 1) which shows the manufacturing method of the semiconductor device by 5th Embodiment of this invention. It is process sectional drawing (the 2) which shows the manufacturing method of the semiconductor device by 5th Embodiment of this invention. It is sectional drawing which shows the structure of the semiconductor device by 6th Embodiment of this invention. It is process sectional drawing (the 1) which shows the manufacturing method of the manufacturing method of the semiconductor device by 6th Embodiment of this invention. It is process sectional drawing which shows the manufacturing method of the manufacturing method of the semiconductor device by 6th Embodiment of this invention. It is the schematic which shows the structure of the semiconductor device by 7th Embodiment of this invention. It is process sectional drawing (the 1) which shows the manufacturing method of the semiconductor device by 7th Embodiment of this invention. It is process sectional drawing (the 2) which shows the manufacturing method of the semiconductor device by 7th Embodiment of this invention. It is a graph which shows the lower limit and upper limit of the V / III ratio at the time of the growth of each quantum dot layer at the time of growing the multiple quantum dot layer in the manufacturing method of the semiconductor device by 7th Embodiment of this invention. It is process sectional drawing (the 3) which shows the manufacturing method of the semiconductor device by 7th Embodiment of this invention. It is a graph (the 1) which shows the growth temperature of an upper cladding layer, the root mean square roughness of the surface of an upper cladding layer, and the relationship between the annealing temperature of a quantum dot, and the blue shift of light emission of a quantum dot. It is the graph (the 2) which shows the relationship between the growth temperature of an upper clad layer, the root mean square roughness of the surface of an upper clad layer, and the annealing temperature of a quantum dot, and the blue shift of light emission of a quantum dot. It is process sectional drawing (the 4) which shows the manufacturing method of the semiconductor device by 7th Embodiment of this invention. It is process sectional drawing which shows the manufacturing method of the semiconductor device by 8th Embodiment of this invention. It is process sectional drawing which shows the growth method of the conventional quantum dot.

DESCRIPTION OF SYMBOLS 10 ... Underlayer 12 ... Sb layer 14 ... Quantum dot layer 16 ... Quantum dot 18 ... InSb layer 20 ... Coating layer 21 ... Thin film 22 ... Cap layer 24 ... GaSb layer 26 ... GaAs substrate 28 ... Buffer layer 30 ... Quantum dot layer 32 ... Quantum dot 34 ... Sb layer 36 ... Cap layer 38 ... GaSb layer 40 ... GaSb layer 42 ... GaSb layer 44 ... Sb layer 46 ... InSb layers 50, 66 ... GaAs substrate 52 ... Buffer layers 54, 68 ... Lower cladding layer 56, 72 ... Active layers 58, 76 ... Upper cladding layers 60, 78 ... Contact layers 62, 80 ... p-side electrodes 64, 82 ... n-side electrodes 70, 74 ... SCH layer 71 ... barrier layer 100 ... underlayer 102 ... Sb layer 104 ... Quantum dot layer 106 ... Quantum dot 108 ... Sb layer 110 ... Cap layer

Claims (5)

Forming a quantum dot on the underlayer by self-organized growth;
Irradiating the surface of the underlayer with Sb or GaSb before the step of forming the quantum dots or during the step of forming the quantum dots;
After the step of forming the quantum dots, a surface layer containing Sb deposited on the surface of the quantum dots by irradiating the surface of the quantum dots with an As source gas for a certain time or etching the surface of the quantum dots. Removing, and
After the step of removing the surface layer, irradiating the surface of the quantum dots with an organic Sb source gas;
And a step of growing a cap layer on the quantum dot after the step of irradiating the organic Sb source gas . In the manufacturing method of the semiconductor device according to claim 1 ,
In the step of irradiating the organic Sb source gas, a group III metal organic source gas is irradiated simultaneously with the organic Sb source gas. In the manufacturing method of the semiconductor device of Claim 1 or 2 ,
Forming an active layer comprising the quantum dots;
A method of manufacturing a semiconductor device, further comprising: growing a clad layer on the active layer using a trimethyl gallium as a Ga material at a growth temperature of 610 to 660 ° C. In the manufacturing method of the semiconductor device of Claim 1 or 2 ,
Forming an active layer comprising the quantum dots;
Growing a cladding layer on the active layer;
A method for manufacturing a semiconductor device, further comprising: growing a contact layer on the clad layer at a growth temperature of 600 to 610 ° C. using triethylgallium as a Ga material. A step of growing a quantum dot layer including quantum dots formed by self-organized growth; and before the step of growing the quantum dot layer or under the step of growing the quantum dot layer. Irradiating the surface of the formation layer with Sb or GaSb; and after forming the quantum dot layer , irradiating the surface of the quantum dots with an As source gas for a certain time or etching the surface of the quantum dots, Removing the surface layer containing Sb deposited on the surface of the quantum dots; after irradiating the surface of the quantum dots with the organic Sb source gas after the step of removing the surface layer; and the organic Sb source after the step of irradiating the gas, on the quantum dot layer, by repeating the step of growing a capping layer on a semiconductor substrate, n layer the quantum dot layer (n is 2 And a step of forming on integer) including the active layer,
In the step of forming the active layer, the quantum of the (i + 1) th layer is larger than the V / III ratio during growth of the quantum dot layer of the i-th layer (i is an integer satisfying 1 ≦ i ≦ n−1). A method of manufacturing a semiconductor device, characterized in that the V / III ratio during the growth of the dot layer is set high.

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