JP4786802B2 - Method for manufacturing semiconductor laser, method for manufacturing optical modulator, and method for manufacturing semiconductor laser with optical modulator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser, an optical modulator, a semiconductor laser with an optical modulator, and a manufacturing method thereof.
[0002]
[Prior art]
A semiconductor laser in which an active region is buried with a high resistance layer is used as a high-speed modulation laser because it can reduce parasitic capacitance. FIG. 15 is a cross-sectional view showing an example of this type of semiconductor laser. In the figure, 1 is an N-type InP substrate, 2 is an N-type cladding layer made of N-type InP (for example, 1 μm thick, carrier concentration P = 1 × 10 18 cm −3), 3 is an InGaAsP strained quantum well active layer, 4 is P-type cladding layer made of P-type InP (for example, thickness 0.5 μm, carrier concentration P = 1 × 10 18 cm −3), 5 is a high-resistance blocking layer made of InP doped with Fe and increased in resistance, Is an N-type InP block layer, 7 is a P-type InP layer, 8 is a P-type InGaAs contact layer, 9 is a P-type electrode (Ti / Pt / Au), and 10 is an N-type electrode (Au / Ge / Ni / Au). is there.
In this semiconductor laser, since the mesa portion is formed by wet etching, it has a gently divergent shape.
[0003]
FIG. 16 is a cross-sectional view showing another example of a conventional semiconductor laser. In the figure, 1 is an N-type InP substrate, 2 is an N-type cladding layer made of N-type InP (for example, thickness 1 μm, carrier concentration P = 1 × 10 18 cm −3), 3 is an InGaAsP strained quantum well active layer, 4 is P-type cladding layer made of P-type InP (for example, thickness 0.5 μm, carrier concentration P = 1 × 10 18 cm −3), 5 is a high-resistance blocking layer made of InP doped with Fe and increased in resistance, Is an N-type InP block layer, 7 is a P-type InP layer, 8 is a P-type InGaAs contact layer, 9 is a P-type electrode (Ti / Pt / Au), and 10 is an N-type electrode (Au / Ge / Ni / Au). is there.
In this semiconductor laser, since the mesa portion is formed by dry etching, it has a vertical shape.
[0004]
The conventional semiconductor laser shown in FIGS. 15 and 16 is configured to block the N-type InP substrate 1 or the N-type cladding layer 2, the high-resistance block layer 5, and the N-type InP block layer 6 stacked at both ends of the mesa portion. As a layer, current can be injected intensively into the InGaAsP strained quantum well active layer 3. However, since the contact width between the P-type cladding layer 4 and the N-type InP block layer 6 is very narrow, leakage current from the contact region tends to flow, often resulting in deterioration of laser oscillation characteristics ( For example, there is a problem that the threshold value increases and the laser efficiency deteriorates.
[0005]
The conventional semiconductor laser shown in FIGS. 15 and 16 can also be used as an optical modulator by using the InGaAsP strained quantum well active layer 3 as a light absorption layer. However, in this case, since the distance between the InGaAsP strain quantum well active layer 3 and the N-type InP block layer 6 is short and the high resistance block layer 5 is thin, there arises a problem that parasitic capacitance increases and high-speed characteristics deteriorate.
[0006]
[Problems to be solved by the invention]
Therefore, in view of the problems of the prior art as described above, according to the present invention, leakage current flows from this portion by taking a sufficient contact length between the N-type InP layer and the mesa portion in the current blocking layer. Semiconductor laser with good laser oscillation characteristics, optical modulator with good optical modulator characteristics, and semiconductor laser with optical modulator with good laser oscillation characteristics and good optical modulator characteristics The purpose is to do.
Another object of the present invention is to provide a semiconductor laser, an optical modulator, and a method of manufacturing a semiconductor laser with an optical modulator having such excellent characteristics.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has the following features.
[0008]
That is, the invention described in claim 1 includes an N-type semiconductor substrate having an N-type electrode formed on the lower surface, an N-type cladding layer made of N-type InP formed on the N-type semiconductor substrate, an active layer, and A mesa portion in which a P-type cladding layer made of P-type InP is laminated, an N-type cladding layer located on both sides of the mesa portion, and Fe formed on both sides of the mesa portion are doped to increase resistance. A current blocking layer having a high resistance block layer made of InP, an N-type InP block layer formed on both sides of the high resistance block layer and on the mesa portion, and formed on the mesa portion and the current block layer. A semiconductor laser comprising a P-type InP layer and a P-type electrode formed on the P-type InP layer via a P-type InGaAs contact layer, wherein the mesa portion, the N-type InP block layer, Contact The length is one that was set to more than 0.05 .mu.m.
[0009]
According to a second aspect of the present invention, there is provided an N-type semiconductor substrate having an N-type electrode formed on the lower surface thereof, an N-type cladding layer made of N-type InP, an active layer, and a P-type formed on the N-type semiconductor substrate. A mesa portion formed by laminating a P-type cladding layer made of InP, an N-type cladding layer located on both sides of the mesa portion, and InP doped with Fe formed on both sides of the mesa portion to increase resistance A current blocking layer having an N-type InP blocking layer formed on the high-resistance blocking layer and on both sides of the mesa portion, and a P-type formed on the mesa portion and the current blocking layer. An optical modulator comprising an InP layer and a P-type electrode formed on the P-type InP layer via a P-type InGaAs contact layer, wherein the mesa portion and the N-type InP block layer Contact length 0.05 In which was set to more than m.
[0010]
According to a third aspect of the present invention, there is provided an N-type semiconductor substrate having an N-type electrode formed on the lower surface, an N-type cladding layer made of N-type InP, an active layer, and a P-type formed on the N-type semiconductor substrate. A mesa portion formed by laminating a P-type cladding layer made of InP, an N-type cladding layer located on both sides of the mesa portion, and InP doped with Fe formed on both sides of the mesa portion to increase resistance A current blocking layer having an N-type InP blocking layer formed on the high-resistance blocking layer and on both sides of the mesa portion, and a P-type formed on the mesa portion and the current blocking layer. A semiconductor laser with an optical modulator, comprising: an InP layer; and a P-type electrode formed on the P-type InP layer via a P-type InGaAs contact layer, wherein the mesa portion and the N-type InP block Contact with layer The length is one that was set to more than 0.05 .mu.m.
[0011]
According to a fourth aspect of the present invention, there is provided an N-type semiconductor substrate having an N-type electrode formed on the lower surface, an N-type cladding layer made of N-type InP, an active layer and a P-type formed on the N-type semiconductor substrate. A mesa portion formed by laminating a P-type cladding layer made of InP, an N-type cladding layer located on both sides of the mesa portion, and InP doped with Fe formed on both sides of the mesa portion to increase resistance A current blocking layer having an N-type InP blocking layer formed on the high-resistance blocking layer and on both sides of the mesa portion, and a P-type formed on the mesa portion and the current blocking layer. A method of manufacturing a semiconductor laser comprising: an InP layer; and a P-type electrode formed on the P-type InP layer via a P-type InGaAs contact layer, wherein the high-resistance block layer is grown and halogenated System Flat embedded in both sides of the mesa portion by repeating the anisotropic etching using the contact length between said mesa the N-type InP blocking layer is a method was set to more than 0.05 .mu.m.
[0012]
According to a fifth aspect of the present invention, there is provided an N-type semiconductor substrate having an N-type electrode formed on the lower surface, an N-type cladding layer made of N-type InP, an active layer, and a P-type formed on the N-type semiconductor substrate. A mesa portion formed by laminating a P-type cladding layer made of InP, an N-type cladding layer located on both sides of the mesa portion, and InP doped with Fe formed on both sides of the mesa portion to increase resistance A current blocking layer having an N-type InP blocking layer formed on the high-resistance blocking layer and on both sides of the mesa portion, and a P-type formed on the mesa portion and the current blocking layer. An optical modulator comprising: an InP layer; and a P-type electrode formed on the P-type InP layer via a P-type InGaAs contact layer, wherein the high-resistance block layer is grown. Halogen gas Flat embedded in both sides of the mesa portion by repeating the anisotropic etching had, contact length between said mesa the N-type InP blocking layer is a method was set to more than 0.05 .mu.m.
[0013]
According to a sixth aspect of the present invention, there is provided an N-type semiconductor substrate having an N-type electrode formed on the lower surface, an N-type cladding layer made of N-type InP, an active layer, and a P-type formed on the N-type semiconductor substrate. A mesa portion formed by laminating a P-type cladding layer made of InP, an N-type cladding layer located on both sides of the mesa portion, and InP doped with Fe formed on both sides of the mesa portion to increase resistance A current blocking layer having an N-type InP blocking layer formed on the high-resistance blocking layer and on both sides of the mesa portion, and a P-type formed on the mesa portion and the current blocking layer. A method of manufacturing a semiconductor laser with an optical modulator, comprising: an InP layer; and a P-type electrode formed on the P-type InP layer via a P-type InGaAs contact layer, wherein the high-resistance block layer is , Growth and ha A method in which anisotropic etching using a gen-based gas is repeated to bury flatly on both sides of the mesa portion so that the contact length between the mesa portion and the N-type InP block layer is 0.05 μm or more. It is.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0015]
Embodiment 1 FIG.
FIG. 1 is a sectional view showing the structure of a semiconductor laser according to the present invention. In the figure, 1 is an N-type InP substrate, 2 is an N-type cladding layer made of N-type InP (for example, 1 μm thick, carrier concentration P = 1 × 10 18 cm −3), 3 is an InGaAsP strained quantum well active layer, 4 is P-type cladding layer made of P-type InP (for example, thickness 0.5 μm, carrier concentration P = 1 × 10 18 cm −3), 5 is a high-resistance blocking layer made of InP doped with Fe and increased in resistance, Is an N-type InP block layer, 7 is a P-type InP layer, 8 is a P-type InGaAs contact layer, 9 is a P-type electrode (Ti / Pt / Au), and 10 is an N-type electrode (Au / Ge / Ni / Au). is there.
[0016]
In this semiconductor laser, an InGaAsP strain quantum well active layer 3 is laminated between an N-type cladding layer 2 and a P-type cladding layer 4 on an N-type InP substrate 1 having an N-type electrode 10 formed on the lower surface thereof. Part. On both sides of the mesa portion, there are provided high resistance block layers 5 which are buried and grown. Further, an N-type InP blocking layer 6 is formed on the high-resistance blocking layer 5 on both sides of the mesa portion, and the N-type cladding layer 2, the high-resistance blocking layer 5 and the N-type InP blocking layer 6 constitute a current blocking layer. is doing. In particular, the N-type InP block layer 6 is formed so that the contact length L with the P-type cladding layer 4 is 0.05 μm or more. In addition, a P-type InP layer 7 is formed so as to cover the upper surface of the mesa portion and the N-type InP block layer 6. A P-type electrode 9 is formed on the upper surface of the P-type InP layer 7 via a P-type InGaAs contact layer 8.
[0017]
In this semiconductor laser, since the contact length L between the P-type cladding layer 4 and the N-type InP block layer 6 is 0.05 μm or more, the P-type cladding layer 4 and the N-type InP block layer 6 The contact area is considerably wider than the conventional one. Therefore, current can be concentrated on the mesa portion, and leakage current from the mesa portion can be suppressed. As a result, the threshold value is lowered and the laser efficiency is improved, and good laser oscillation characteristics can be obtained.
In this semiconductor laser, the N-type InP block layer 6 is formed at a position away from the InGaAsP strain quantum well active layer 3. Therefore, since the high resistance block layer 5 can be formed thick, the parasitic capacitance is reduced, and high speed characteristics can be improved.
[0018]
Next, a method for manufacturing a semiconductor laser according to the present invention will be described. 2 to 13 are diagrams for explaining the manufacturing process of this semiconductor laser.
[0019]
First, as shown in FIG. 2, an N-type cladding layer 2 made of N-type InP, an InGaAsP strained quantum well active layer 3, and a P-type InP on an N-type InP substrate 1 whose upper surface is a (001) plane by MOCVD. A P-type cladding layer 4 made of is grown (first step). Next, as shown in FIG. 3, a SiO2 insulating film 11 is formed on the P-type cladding layer 4 and patterned (second step). Next, as shown in FIG. 4, a vertical mesa portion is formed by removing the semiconductor layers on both sides of the SiO2 insulating film 11 to the middle of the N-type cladding layer 2 by methane-based dry etching or the like. Process). Next, as shown in FIG. 5, while flowing hydrogen chloride (HCl) gas by MOCVD, the high resistance block layer 5a made of InP doped with Fe is made thin (for example, about 0.1 μm). (4th process). Here, in the present invention, since the upper surface of the N-type InP substrate 1 is formed in the (001) plane, the upper surfaces of the respective layers such as the N-type cladding layer 2 and the high-resistance block layer 5a become the (001) plane. It is formed. When the high resistance block layer 5a is grown while flowing hydrogen chloride gas, the growth rate of the (110) plane in contact with the side surface of the mesa portion is slower than that of the (001) surface which is the upper surface, and the high resistance covering the side surface of the mesa portion is high. The layer thickness of the block layer 5a can be reduced.
[0020]
Next, the growth of the high resistance block layer 5a is interrupted, and phosphine (PH3) and hydrogen chloride gas are allowed to flow in the MOCVD furnace. Hydrogen chloride gas has the property of etching the InP layer, and in particular, the etching rate on the (001) plane is much slower than the etching rate on the (110) plane (see FIG. 14). Therefore, the etching of the high resistance block layer 5a in the side direction of the mesa portion is completed before the etching of the high resistance block layer 5a in the thickness direction of the N-type cladding layer 2 is almost completed. By using this property, only the InP layer covering the side surface of the mesa portion can be selectively etched, and the structure shown in FIG. 6 can be completed (fifth step).
Although hydrogen chloride gas is used here, the same effect can be obtained by using other halogen-based gases. Further, the same effect can be obtained in other surface directions where anisotropic etching is possible. However, if the method of the present invention is performed by wet etching instead of dry etching, each layer is etched in the same direction, so that the structure shown in FIG. 6 cannot be obtained.
[0021]
Next, as shown in FIG. 7, the high resistance block layer 5b made of InP doped with Fe and made highly resistive while flowing hydrogen chloride gas by the MOCVD method is thinned (for example, with a thickness of about 0.1 μm). ) Grow (sixth step). Then, the growth of the high resistance block layer 5b is interrupted, phosphine and hydrogen chloride gas are allowed to flow in the MOCVD furnace, and only the high resistance block layer 5b covering the side surface of the mesa portion is selectively etched to obtain the structure shown in FIG. Completed (seventh step). Thereafter, the sixth and seventh steps are repeated, and only the high-resistance block layer covering the side surface of the mesa portion is etched, and the high-resistance block layer 5 is flatly buried on both sides of the mesa portion to complete the structure shown in FIG. (Eighth step).
[0022]
Next, as shown in FIG. 10, an N-type InP block layer 6 is grown on the high resistance block layer 5 in a MOCVD furnace (ninth step). Here, since the high-resistance block layer 5 is formed flat in the previous step, the contact length L between the mesa portion and the N-type InP block layer 6 is set to 0.05 μm or more without special measures. be able to. Thereafter, as shown in FIG. 11, the SiO2 insulating film 11 is removed (tenth step). Next, as shown in FIG. 12, a P-type InP layer 7 and a P-type InGaAs contact layer 8 are grown by MOCVD (11th step). Finally, as shown in FIG. 13, a P-type electrode (Ti / Pt / Au) 9 and an N-type electrode (Au / Ge / Ni / Au) 10 are formed (a twelfth step).
[0023]
Through the above-described steps, the semiconductor laser according to the present invention can be completed.
[0024]
Embodiment 2. FIG.
Although the semiconductor laser has been described so far, in the present invention, an optical modulator having a layer configuration similar to that shown in FIG. That is, by operating the InGaAsP strained quantum well layer 5 used as the active layer as a light absorption layer in the semiconductor laser, the light absorption rate of the light absorption layer becomes a voltage applied to the P-type electrode 9 and the N-type electrode 10. It changes correspondingly and functions as an optical modulator.
Since the optical modulator configured in this way can suppress the leakage current from flowing for the same reason as the semiconductor laser described above, good optical modulator characteristics can be obtained.
[0025]
This optical modulator can also be manufactured by a method similar to the semiconductor laser manufacturing method described in the first embodiment.
[0026]
Embodiment 3 FIG.
As described in the second embodiment, the semiconductor laser according to the present invention also functions as an optical modulator. Therefore, by integrally forming the semiconductor laser shown in the first embodiment and the optical modulator shown in the second embodiment on the same semiconductor substrate, the function as the semiconductor laser and the function as the optical modulator are achieved. It is also possible to construct a semiconductor laser with an optical modulator that has both. For example, if the P-type electrode is separated by the semiconductor laser part and the optical modulator part and each control voltage is applied independently, the laser light output from the semiconductor laser is modulated by the optical modulator. Can output.
Since this semiconductor laser with an optical modulator can also suppress the leakage current from flowing for the same reason as the semiconductor laser described above, good laser oscillation characteristics and optical modulator characteristics can be obtained.
[0027]
This semiconductor laser with an optical modulator can also be manufactured by the same method as the semiconductor laser manufacturing method described in the first embodiment.
[0028]
【The invention's effect】
Since the present invention has the configuration as described above, the following effects can be obtained.
[0029]
That is, according to the first aspect of the present invention, since a sufficient contact length between the N-type InP layer and the mesa portion in the current blocking layer can be obtained, the leakage current from this portion can be suppressed, so that a good laser can be obtained. A semiconductor laser having oscillation characteristics can be obtained.
In this semiconductor laser, the N-type InP block layer is formed at a position away from the InGaAsP strained quantum well active layer, and the high-resistance block layer is formed thick, so that the parasitic capacitance is reduced and the high-speed characteristics are improved. be able to.
[0030]
According to the second aspect of the present invention, since a sufficient contact length between the N-type InP layer and the mesa portion in the current blocking layer can be obtained, the leakage current from this portion can be suppressed. An optical modulator having characteristics can be obtained.
In this optical modulator, the N-type InP block layer is formed at a position away from the InGaAsP strained quantum well active layer and the high-resistance block layer is formed thick, so the parasitic capacitance is reduced and the high-speed characteristics are improved. Can be made.
[0031]
According to the third aspect of the present invention, since the contact length between the N-type InP layer and the mesa portion in the current blocking layer is sufficiently long, the leakage current from this portion can be suppressed, so that the good laser oscillation characteristics And a semiconductor laser with an optical modulator having optical modulator characteristics.
In this semiconductor laser with an optical modulator, the N-type InP block layer is formed at a position away from the InGaAsP strained quantum well active layer, and the high-resistance block layer is formed thick. Characteristics can be improved.
[0032]
According to the fourth aspect of the present invention, a semiconductor laser manufacturing method having good laser oscillation characteristics and high speed characteristics can be obtained.
[0033]
According to the fifth aspect of the present invention, a method of manufacturing an optical modulator having good optical modulator characteristics and high speed characteristics can be obtained.
[0034]
According to the sixth aspect of the present invention, a method for manufacturing a semiconductor laser with an optical modulator having good optical modulator characteristics, laser oscillation characteristics, and high-speed characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of a semiconductor laser according to the present invention.
FIG. 2 is a drawing for explaining the manufacturing process of the semiconductor laser according to the present invention.
FIG. 3 is a drawing for explaining the manufacturing process of the semiconductor laser according to the present invention.
FIG. 4 is a diagram for explaining a manufacturing process of the semiconductor laser according to the present invention.
FIG. 5 is a diagram for explaining a manufacturing process of the semiconductor laser according to the present invention.
FIG. 6 is a drawing for explaining the manufacturing process for the semiconductor laser according to the present invention.
FIG. 7 is a drawing for explaining the manufacturing process of the semiconductor laser according to the present invention.
FIG. 8 is a drawing for explaining the manufacturing process for the semiconductor laser according to the present invention.
FIG. 9 is a drawing for explaining the manufacturing process for the semiconductor laser according to the present invention.
FIG. 10 is a drawing for explaining the manufacturing process for the semiconductor laser according to the present invention.
FIG. 11 is a drawing for explaining the manufacturing process for the semiconductor laser according to the present invention.
FIG. 12 is a drawing for explaining the manufacturing process for the semiconductor laser according to the present invention.
FIG. 13 is a drawing for explaining the manufacturing process for the semiconductor laser according to the present invention.
FIG. 14 is a graph showing the plane orientation dependence of the etching rate of the InP layer.
FIG. 15 is a cross-sectional view showing a configuration of a conventional semiconductor laser.
FIG. 16 is a cross-sectional view showing a configuration of a conventional semiconductor laser.
[Explanation of symbols]
1 N-type InP substrate, 2 N-type cladding layer, 3 InGaAsP strained quantum well active layer, 4 P-type cladding layer, 5 High resistance block layer, 6 N-type InP block layer, 7 P-type InP layer, 8 P-type InGaAs contact Layer, 9 P-type electrode, 10 N-type electrode, 11 SiO2 insulating film.

Claims (3)

  An N-type semiconductor substrate having an N-type electrode formed on the lower surface;
  A mesa portion formed on the N-type semiconductor substrate, in which an N-type cladding layer made of N-type InP, an active layer, and a P-type cladding layer made of P-type InP are laminated;
  N-type cladding layers located on both sides of the mesa portion; a high resistance block layer made of InP doped with Fe and formed on both sides of the mesa portion; and on the high resistance block layer and the high resistance block layer A current blocking layer having an N-type InP blocking layer formed on both sides of the mesa portion;
  A P-type InP layer formed on the mesa portion and the current blocking layer;
  A method of manufacturing a semiconductor laser comprising: a P-type electrode formed on a P-type InP layer via a P-type InGaAs contact layer;
  The high resistance block layer is flatly embedded on both sides of the mesa portion by repeating growth and anisotropic etching using a halogen-based gas, and the contact length between the mesa portion and the N-type InP block layer is zero. A method for manufacturing a semiconductor laser, characterized in that the thickness is 0.05 μm or more.   An N-type semiconductor substrate having an N-type electrode formed on the lower surface;
  A mesa portion formed on the N-type semiconductor substrate, in which an N-type cladding layer made of N-type InP, an active layer, and a P-type cladding layer made of P-type InP are laminated;
  N-type cladding layers located on both sides of the mesa portion; a high resistance block layer made of InP doped with Fe and formed on both sides of the mesa portion; and on the high resistance block layer and the high resistance block layer A current blocking layer having an N-type InP blocking layer formed on both sides of the mesa portion;
  A P-type InP layer formed on the mesa portion and the current blocking layer;
  A method of manufacturing an optical modulator comprising a P-type electrode formed on a P-type InP layer via a P-type InGaAs contact layer,
  The high resistance block layer is flatly embedded on both sides of the mesa portion by repeating growth and anisotropic etching using a halogen-based gas, and the contact length between the mesa portion and the N-type InP block layer is zero. A method of manufacturing an optical modulator, characterized in that the thickness is 0.05 μm or more.   An N-type semiconductor substrate having an N-type electrode formed on the lower surface;
  A mesa portion formed on the N-type semiconductor substrate, in which an N-type cladding layer made of N-type InP, an active layer, and a P-type cladding layer made of P-type InP are laminated;
  N-type cladding layers located on both sides of the mesa portion; a high resistance block layer made of InP doped with Fe and formed on both sides of the mesa portion; and on the high resistance block layer and the high resistance block layer A current blocking layer having an N-type InP blocking layer formed on both sides of the mesa portion;
  A P-type InP layer formed on the mesa portion and the current blocking layer;
  A method of manufacturing a semiconductor laser with an optical modulator, comprising: a P-type electrode formed on a P-type InP layer via a P-type InGaAs contact layer;
  The high resistance block layer is flatly embedded on both sides of the mesa portion by repeating growth and anisotropic etching using a halogen-based gas, and the contact length between the mesa portion and the N-type InP block layer is zero. A method for manufacturing a semiconductor laser with an optical modulator, wherein the thickness is 0.05 μm or more.

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