JP4100817B2 - Semiconductor light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light emitting device.
[0002]
[Prior art]
The AlGaInP-based material is the largest direct transition material among III-V semiconductors except for the AlGaInN-based material and B (boron) -based material, and has a maximum band gap energy of about 2.3 eV (wavelength 540 nm). can get. For this reason, research and development have been carried out as materials for light-emitting elements such as high-intensity green to red light-emitting diodes conventionally used for color displays and the like, and for visible light semiconductor lasers used for optical writing for laser printers, CDs, DVDs, etc. It is. Among these, in particular, a material that lattice-matches to a GaAs substrate is used for a semiconductor laser. In particular, for high-density recording or the like, an element that operates stably at high temperature and high output and has a short wavelength is required.
[0003]
In order to manufacture a semiconductor laser, it is necessary to use a clad layer (made of a material having a larger band gap than the active layer) and to confine carriers and light in the active layer (light emitting layer). In the case of a short wavelength with a normal bulk active layer double hetero (DH) structure, it is necessary to use AlGaInP doped with Al for the active layer. The addition of Al has the effect of increasing the band gap, but since Al is very active, it combines with the slight amount of oxygen in the atmosphere and raw materials during growth to form a deep level, leading to a decrease in luminous efficiency. Since the Al composition is easy, a smaller Al composition is preferable. Therefore, as another method for shortening the oscillation wavelength, an SCH-QW (Separate Confinement Heterostructure-Quantum Well) using a GaInP quantum well structure for the active layer (well layer) and AlGaInP as the light guide layer is used. The way is done. Further, in order to lower the threshold value, a strained quantum well structure in which a strain is applied to a quantum well layer is generally used as disclosed in JP-A-6-77592. In this case, since the lattice constant of the strain quantum well layer is different from that of the substrate, a thickness equal to or less than the critical film thickness at which lattice relaxation occurs can be used. Japanese Patent Laid-Open No. 6-275915 discloses that tensile strain is more effective as a type of strain for a short wavelength laser such as the 635 nm band. Since the tensile strain well layer is GaInP having a composition close to GaP with respect to GaAs as a substrate, a wide gap is formed, and a well layer having an appropriate thickness can be used as a well layer for the compressive strain well layer. The main reason is that the adverse effects of can be reduced. However, if a tensile strain well layer is used, the mode becomes TM mode, so the polarization differs from that of a normal semiconductor laser (TE mode) in other wavelength bands by 90 °. .
[0004]
However, (Al_xGa_1-x)_0.5In_0.5Light is confined in the P light guide layer, but since the Al composition x is usually as large as about 0.5, end face breakage is likely to occur due to surface recombination caused by Al at the end face serving as the laser cavity surface. It was difficult to produce a stable operation for a long time.
[0005]
Also, when an AlGaInP heterojunction is formed, the band offset ratio of the conduction band is small, and the band discontinuity (ΔEc) between the active layer (light emitting layer) and the clad layer on the conduction band side is small, so that injected carriers (electrons) are active. There is a problem that the temperature dependence of the oscillation threshold current of the semiconductor laser is large and the temperature characteristics are poor, because the layer tends to overflow from the layer to the cladding layer. This problem becomes more prominent as the wavelength becomes shorter. For example, when compared with red lasers in the 635 nm band and the 650 nm band, the high temperature characteristics of the 635 nm band laser are overwhelmingly bad despite the slight wavelength difference.
[0006]
In order to solve such a problem, Japanese Patent Application Laid-Open No. 4-114486 discloses a structure in which a multiple quantum barrier (MQB) structure in which a number of very thin layers are stacked is provided between an active layer and a cladding layer to confine injected carriers. Proposed. However, in this case, the structure becomes complicated, and in order to obtain the effect, it is necessary to improve the thickness control and to flatten the interface of each layer at the atomic layer level. It was difficult.
[0007]
As described above, the conventional GaAs substrate lattice-matching material has limitations in temperature characteristics and wavelength reduction, and operates at a high temperature (for example, 80 °), a high output (for example, 30 mW or more), and a stable operation (for example, 10,000 hours). It has been difficult to realize a laser having a wavelength of 635 nm or shorter. As described above, an AlGaInP material having a lattice constant smaller than that of GaAs is advantageous in shortening the wavelength because it has a wider gap than a material that can be grown on a GaAs substrate. There has been proposed a short wavelength laser using such other material system and having an oscillation wavelength of 600 nm or less. For example, Al is used as a cladding layer on a GaP substrate._yGa_1-yUsing P (0 ≦ y ≦ 1), direct transition type compressive strain Ga as an active layer_xIn_1-xJapanese Patent Laid-Open No. 6-53602 proposes an element in which P (0 <x <1) is used and N is doped in the active layer as an impurity of an isoelectronic trap. However, this structure has an advantage that the wavelength can be shortened by using a material having a low Al content in the active layer, but the lattice constant is the closest to GaP and a direct transition occurs._0.7In_0.3The P active layer also has a 2.3% lattice mismatch with the GaP substrate, and the critical film thickness at which misfit dislocations due to the lattice mismatch do not occur becomes thin.
[0008]
Moreover, it has a lattice constant between GaAs and GaP on a GaAs substrate (AlGa)_aIn_1-aGaP that lattice-matches a double heterostructure made of P (0.51 <a ≦ 0.73)_xAs_1-xAn element formed through a buffer layer or the like is proposed in JP-A-5-41560. In this technique, the buffer layer eliminates lattice irregularities between the substrate and the double heterostructure. FIG. 1 shows the relationship between the lattice constant and the band gap energy. In FIG. 1, the solid line represents the direct transition material, and the broken line represents the indirect transition material. Has a lattice constant between GaAs and GaP (AlGa)_aIn_1-aThe P (0.51 <a ≦ 0.73) material is a material in a range surrounded by AlInP and GaInP. In this technique, AlGaInP having a wider gap than that of the GaAs substrate lattice matching material can be used for the cladding layer and the active layer, which is advantageous for shortening the wavelength of a laser having a wavelength shorter than 600 nm. However, the laser proposed in Japanese Patent Laid-Open No. 5-41560 has a structure for realizing a laser having a wavelength shorter than 600 nm, and is not a structure considering a laser having a wavelength longer than 600 nm such as 635 nm and 650 nm bands. . For example, it can be seen that the dependence of the band gap on the lattice constant is larger in the GaInP range up to 0.73 in GaInP than in the indirect transition material AlInP. Since a wide gap material is suitable for the clad layer, it is better to use Al (Ga) InP having a lattice constant close to that of GaP, but conversely, it becomes a material for the active layer in the 635 nm and 650 nm bands ( The lattice constant of Al) GaInP deviated greatly from that of the cladding layer, and had a large compressive strain, which was not preferable.
[0009]
[Problems to be solved by the invention]
The present invention provides a semiconductor light emitting device such as a 635 nm or 650 nm band red semiconductor laser that operates stably at high temperature, high output, and visible light, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, or a visible light emitting diode with high luminous efficiency. The purpose is that.
[0010]
[Means for Solving the Problems]
  In order to achieve the above object, the invention according to claim 1 is a semiconductor light emitting device in which a heterojunction having an active layer for generating light and a cladding layer for confining light is formed on a semiconductor substrate.
Active layerContains As ( Al _x Ga _1-x ) _α In _1-α P _t As _1-t ( 0 ≦ x <1, 0 <α1 ≦ 1, 0 ≦ t <1 )Consists of
The cladding layer contains Al having a larger band gap than the active layer and having a lattice constant between GaP and GaAs (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1).
[0017]
  Also,Claim 2The described invention is claimed.1In the semiconductor light emitting device described above, the semiconductor substrate is made of GaPAs, and the heterojunction portion is crystal-grown on the semiconductor substrate.
[0018]
  Also,Claim 3The described invention is claimed.1In the semiconductor light emitting device described above, the semiconductor substrate is made of GaAs or GaP, and the heterojunction portion is crystal-grown between the semiconductor substrate and the cladding layer via a relaxation buffer layer that relaxes lattice mismatch between the two. It is a feature.
[0019]
  Also,Claim 4The described inventionClaim 3In the semiconductor light-emitting device described above, the relaxation buffer layer is characterized by comprising a graded layer whose lattice constant gradually changes from the lattice constant of the semiconductor substrate in the growth direction and approaches the lattice constant of the cladding layer.
[0020]
  Also,Claim 5The described inventionClaim 3In the described semiconductor light emitting device, the relaxation buffer layer is characterized by having a strained superlattice structure in which at least two kinds of materials having different lattice constants are alternately stacked.
[0021]
  Also,Claim 6The described inventionClaim 3In the described semiconductor light emitting device, the relaxation buffer layer is characterized by comprising a low-temperature buffer layer grown at a temperature lower than the growth temperature of the cladding layer.
[0022]
  Also,Claim 7The described inventionClaim 3ThruClaim 6In the semiconductor light emitting device according to any one of the above, the relaxation buffer layer is made of GaInP or GaPAs.
[0023]
  Also,Claim 8The described inventionClaim 2OrClaim 3In the semiconductor light-emitting element described above, the plane orientation of the semiconductor substrate is a plane inclined in the range of 0 ° to 54.7 ° in the [011] direction from the (100) plane, or [0-11] from the (100) plane. The surface is inclined in the range of 10 ° to 54.7 ° in the direction or a surface equivalent to these.
[0024]
  Also,Claim 9The described inventionClaim 2OrClaim 3In the semiconductor light-emitting device described above, the surface of the GaPAs substrate is planarized by mechanical polishing before the heterojunction is crystal-grown, or after the growth of the relaxation buffer layer and before the heterojunction is crystal-grown. The surface is flattened by mechanical polishing.
[0025]
  Also,Claim 10The described inventionClaim 2OrClaim 3The semiconductor light-emitting element described above is characterized in that a layer whose upper surface at the interface of the layer is flatter than the lower surface (substrate side) is provided between the semiconductor substrate and the heterojunction portion.
[0026]
  Also,Claim 11The described inventionClaim 10In the semiconductor light-emitting element described above, a layer whose upper surface at the interface of the layer is flatter than the lower surface (substrate side) is Se 5 × 10¹⁸cm^-3It is characterized by being GaInP doped as described above.
[0027]
  Also,Claim 12The described inventionClaim 3In the described semiconductor light emitting device, the relaxation buffer layer has Se of 5 × 10 5.¹⁸cm^-3It is characterized by being GaInP doped as described above.
[0028]
  Also,Claim 13The invention described in claims 1 toClaim 12In the semiconductor light emitting device according to any one of the above, the heterojunction portion is grown by a metal organic chemical vapor deposition method or a molecular beam epitaxy method.
[0029]
  Also,Claim 14The described inventionClaim 13In the semiconductor light emitting device described above, the relaxation buffer layer is grown by a metal organic chemical vapor deposition method or a molecular beam epitaxy method.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a diagram showing a configuration example of a semiconductor light emitting element according to the present invention. Referring to FIG. 2, in this semiconductor light emitting device, a heterojunction 4 having an active layer 2 for generating light and a cladding layer 3 for confining light is formed on a semiconductor substrate 1 of GaAs.
[0031]
Here, in the first embodiment of the present invention, the active layer 2 is made of (Al_xGa_1-x)_αIn_1-αP_tAs_1-t(0 ≦ x <1, 0 <α ≦ 1, 0 ≦ t ≦ 1), and the cladding layer 3 has a larger band gap than the active layer 2 and contains Al having a lattice constant between GaP and GaAs. (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1).
[0032]
In the first embodiment, the cladding layer 3 contains Al having a lattice constant between GaP and GaAs (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1), which has a larger band gap than the cladding layer material that can be formed on the GaAs semiconductor substrate 1 and is advantageous for shortening the wavelength. The active layer 2 is made of (Al_xGa_1-x)_αIn_1-αP_tAs_1-t(0 ≦ x <1, 0 <α ≦ 1, 0 ≦ t ≦ 1), so that the cladding layer 3 can be distorted and the energy gap is narrower than the conventional material (narrow gap). You can also For this reason, the range of device design is widened more than before, and good characteristics can be obtained not only for wavelengths shorter than 600 nm but also for light-emitting devices having wavelengths longer than 600 nm.
[0033]
Further, in the second embodiment of the present invention, in the semiconductor light emitting device of FIG._xGa_1-x)_αIn_1-αP_tAs_1-t(0.ltoreq.x <1, 0 <.alpha..ltoreq.1, 0.ltoreq.t.ltoreq.1) Al is a single quantum well, and the cladding layer 3 has a larger band gap than the active layer 2 and has a lattice constant between GaP and GaAs. (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1), and in the heterojunction portion 4, between the active layer 2 and the cladding layer 3, as shown in FIG. The band gap is larger than the active layer 2 and smaller than the cladding layer 3 (Al_zGa_1-z)_γIn_1-γP_uAs_1-uA light guide layer 5 made of (0 ≦ z <1, 0.5 <γ <1, 0 <u ≦ 1) is provided.
[0034]
In this second embodiment, the cladding layer 3 contains Al having a lattice constant between GaP and GaAs (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1), which has a larger band gap than the cladding layer material that can be formed on the GaAs semiconductor substrate 1 and is advantageous for shortening the wavelength. Also, (Al_zGa_1-z)_γIn_1-γP_uAs_1-uThe light guide layer 5 made of (0 ≦ z <1, 0.5 <γ <1, 0 <u ≦ 1) and (Al_xGa_1-x)_αIn_1-αP_tAs_1-tSince the SCH structure is formed by the active layer 2 of a single quantum well consisting of (0 ≦ x <1, 0 <α ≦ 1, 0 ≦ t ≦ 1), it is wide with a smaller Al composition than the GaAs substrate lattice matching material. A gap can be obtained, the Al composition of the light guide layer 5 can be reduced as compared with the conventional case, the luminous efficiency can be improved by reducing the non-radiative recombination current, reducing the surface recombination current, etc. In this case, the end face is hardly deteriorated, and stable operation is possible even at high output. Further, the clad layer 3 can be distorted, and the energy gap can be made narrower (a narrow gap) than that of the conventional material. Furthermore, GaInP has a smaller lattice constant and a smaller band gap as the Ga composition is reduced. Referring to the estimation of band discontinuity by Sandip et al. (Appl. Phys. Lett. 60, 1992, pp 630 to 632), the change of the band gap occurs on the conduction band side, and the energy on the valence band side is almost changed. Absent. That is, even if the composition is changed, the change in energy of the valence band is small. On the other hand, when Al is added to GaInP, the conduction band energy increases and the valence band energy decreases. The change is larger on the valence band side. Conventionally, in a structure on a GaAs substrate, AlGaInP having a large Al composition has to be used as a light guide layer, and has a large band discontinuity on the valence band side with the GaInP quantum well layer. That is, the band discontinuity on the conduction band side was not sufficiently large. On the other hand, according to the second embodiment of the present invention, since the Al composition of the light guide layer 5 can be reduced, a large conduction band discontinuity can be obtained. As a result, carrier (electron) overflow due to a small band discontinuity on the conduction band side, which has been a problem with red lasers using conventional AlGaInP-based materials, can be significantly improved. For this reason, since the range of element design is widened more than ever, good characteristics can be obtained not only for wavelengths shorter than 600 nm but also for light-emitting elements having wavelengths longer than 600 nm.
[0035]
In the third embodiment of the present invention, in the semiconductor light emitting device of FIG. 2, the active layer 2 of the heterojunction portion 4 has a quantum well structure composed of a well layer and a barrier layer. Al_x1Ga_1-x1)_α1In_1-α1P_t1As_1-t1(0 ≦ x1 <1, 0 <α1 ≦ 1, 0 ≦ t1 ≦ 1), and the barrier layer is (Al_x2Ga_1-x2)_α2In_1-α2P_t2As_1-t2(0 ≦ x2 <1, 0.5 <α2 <1, 0 ≦ t2 ≦ 1), the clad layer 3 has a band gap larger than that of the active layer 2, and has Al having a lattice constant between GaP and GaAs. Included (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1), and in the heterojunction portion 4, between the active layer 2 and the cladding layer 3, as shown in FIG. The band gap is larger than the active layer 2 and smaller than the cladding layer 3 (Al_zGa_1-z)_γIn_1-γP_uAs_1-uA light guide layer 5 made of (0 ≦ z <1, 0.5 <γ <1, 0 <u ≦ 1) is provided.
[0036]
In the third embodiment, the cladding layer 3 contains Al having a lattice constant between GaP and GaAs (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1), which has a larger band gap than the clad layer material that can be formed on the GaAs semiconductor substrate 1, and is advantageous for shortening the wavelength. Also, (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(5 ≦ g <1, 0.5 <γ <1, 0 <u ≦ 1), the light guide layer 5 and (Al_x1Ga_1-x1)_α1In_1-α1P_t1As_1-t1A quantum well composed of (0 ≦ x1 <1, 0 <α1 ≦ 1, 0 ≦ t1 ≦ 1) and (Al_x2Ga_1-x2)_α2In_1-α2P_t2As_1-t2Since the SCH structure is formed by the barrier layer composed of (0 ≦ x2 <1, 0 <α2 ≦ 1, 0 ≦ t2 ≦ 1), the Al composition of the light guide layer 5 can be reduced compared to the conventional case, and no light emission Luminous efficiency can be improved by reducing the recombination current, reducing the surface recombination current, etc., and in the case of a laser, the end face is hardly deteriorated, and stable operation is possible even at high output. Also, the well layer can be distorted with respect to the cladding layer 3, and the strain direction of the barrier layer is opposite to that of the well layer to compensate the strain of the well layer to obtain a good quantum well structure. You can also. In addition, the multi-quantum well structure makes it possible to sufficiently confine carriers in the well layer. In addition, the energy gap can be narrowed (a narrow gap) as compared with conventional materials. Furthermore, in GaInP, when the Ga composition is decreased, the lattice constant increases and the band gap decreases. Referring to the estimation of band discontinuity by Sandip et al. (Appl. Phys. Lett. 60, 1992, pp 630 to 632), the change in the band gap occurs on the conduction band side, and the energy on the valence band side hardly changes. . That is, even if the composition is changed, the change in energy of the valence band is small. On the other hand, when Al is added to GaInP, the conduction band energy increases and the valence band energy decreases. The change is larger on the valence band side. Conventionally, in a structure on a GaAs substrate, AlGaInP having a large Al composition has to be used as a light guide layer, and has a large band discontinuity on the valence band side with the GaInP quantum well layer. That is, the band discontinuity on the conduction band side was not sufficiently large. On the other hand, according to the third embodiment of the present invention, since the Al composition of the light guide layer 5 can be reduced, a large conduction band discontinuity can be obtained. As a result, carrier (electron) overflow due to small band discontinuity on the conduction band side, which has been a problem with conventional red lasers using AlGaInP materials, can be remarkably improved, and the temperature characteristics are good with a low threshold. For this reason, since the range of device design is widened more than ever, good characteristics can be obtained not only for wavelengths shorter than 600 nm, but also for light-emitting devices having wavelengths longer than 600 nm.
[0037]
In the fourth embodiment of the present invention, in the semiconductor light emitting device of the first, second, or third embodiment, the active layer 2 contains As (Al_xGa_1-x)_αIn_1-αP_tAs_1-t(0 ≦ x <1, 0 <α1 ≦ 1, 0 ≦ t ≦ 1).
[0038]
In this fourth embodiment, the addition of As reduces the band gap, so even when the cladding layer 3 having a large band gap close to GaP is used, the cladding constant is longer than 600 nm such as 635 nm and 650 nm bands. It can correspond to an element. That is, the clad layer 3 has a larger band gap than the conventional 635 nm and 650 nm band devices on the GaAs semiconductor substrate, carrier overflow is reduced, and good device characteristics such as high-temperature stable operation can be obtained.
[0039]
In the fifth embodiment of the present invention, in the semiconductor light emitting device of the second, third, or fourth embodiment, the light guide layer 5 includes Ga that does not contain Al._γIn_1-γP_uAs_1-u(0.5 <γ <1, 0 <u ≦ 1).
[0040]
In the fifth embodiment, the band gap is increased when the lattice constant is smaller than that of GaAs, and the Al composition can be reduced in order to obtain the same band gap material. According to the embodiment, the Al composition of the light guide layer 5 can be reduced as compared with the conventional case. For example, in a red laser on a GaAs semiconductor substrate 1, a band gap wavelength is usually about 570 nm (Al_0.5Ga_{0 . 5})_0.5In_0.5P is used, but according to the material having a lattice constant between GaP and GaAs of the fifth embodiment, Ga containing no Al is used._0.7In_0.3This bandgap wavelength is achieved by P. For this reason, even in red lasers such as 635 nm and 650 nm bands, the active region can be formed of a material that does not contain Al, and the non-light-emitting recombination current and surface recombination current caused by Al can be reduced. Therefore, the end face is hardly deteriorated, and stable operation is possible even at high output.
[0041]
In the sixth embodiment of the present invention, in the semiconductor light emitting device of the first, second, third, fourth, or fifth embodiment, the cladding layer contains As (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v <1).
[0042]
GaP, GaAs, GaP with small inclination from (100) plane and (100)_0.4As_0.6When AlGaInP was grown on the substrate by MOCVD or the like, many hill-like defects called hillocks were observed on the growth surface. This was particularly remarkable when the Al composition such as AlInP was large. If a large number of hillocks are present in the growth layer, the device characteristics such as laser and LED are deteriorated and the yield is lowered, which is not preferable in production. During the growth, Al or Ga forms droplets, which serve as nuclei to form hillocks. The inventors of the present application have found that the density of hillocks can be drastically reduced by including As during AlGaInP growth. 11 (a) and 11 (b) show GaP that is 2 ° off from the (100) plane in the [110] direction._0.4As_0.6The surface Nomarski (surface morphology) photograph of AlInP (FIG. 11 (a)) and AlInPAs (FIG. 11 (b)) on an epitaxial substrate is shown. Here, AlInP in FIG. 11A and AlInPAs in FIG. 11B were grown at 750 ° C. The As composition of AlInPAs was about 10%. Hillocks depend on the growth conditions, and the hillock density could be reduced by raising the growth temperature of AlInP from 700 ° C. to 750 ° C., but it is still large as shown in FIG. However, by adding As, the hillock density could be drastically reduced as shown in FIG. 11 (b). Similarly, even when the growth temperature was lowered to 700 ° C., the hillock density decreased drastically. This is presumably because the formation of Al or Ga droplets is suppressed. Even a small As composition was effective, and the larger the As composition, the greater the effect of reducing the hillock density. Due to the effect of reducing hillocks due to the addition of As, it is possible to suppress deterioration of device characteristics and yield reduction.
[0043]
In the seventh embodiment of the present invention, in the semiconductor light emitting device of the second, third, fourth, fifth, or sixth embodiment, the lattice constant of the well layer is larger than that of the cladding layer, and the compressive strain is increased. It has become.
[0044]
In a conventional 635 nm band laser on a GaAs substrate, a compression strain well layer results in a material with a small band gap (mainly GaInP), the well width becomes too narrow, and the influence of the interface becomes large, making it difficult to obtain good performance. Therefore, a tensile strain well layer is used. For this reason, polarization was TM mode. On the other hand, in the sixth embodiment of the present invention, since the band gap is increased, even when a material having a larger lattice constant than the cladding layer 3 is used for the well layer, a quantum well layer having an optimum thickness can be formed. A high-performance compression strain 635 nm band laser structure can be easily obtained. In addition, since it has a compressive strain, the polarized light becomes a TE mode, which is the same as a general laser of another wavelength band and can be used without changing the optical system.
[0045]
In the eighth embodiment of the present invention, in the semiconductor light emitting device of the first, second, third, fourth, fifth, sixth or seventh embodiment, the semiconductor substrate 1 is made of GaPAs. A heterojunction portion 4 is crystal-grown on the semiconductor substrate 1.
[0046]
In the eighth embodiment, a GaPAs having a lattice constant between GaP and GaAs is grown thick on a GaP or GaAs substrate 1 (for example, to a thickness of 30 μm) and can be substantially regarded as a GaPAs substrate. It can be grown by VPE (vapor phase epitaxy) method or the like. Then, by making the uppermost portion the same as the lattice constant of the heterojunction portion 4 (at least the cladding layer 3), this material system can be grown without lattice irregularities.
[0047]
In the ninth embodiment of the present invention, in the semiconductor light emitting device of the first, second, third, fourth, fifth, sixth or seventh embodiment, the semiconductor substrate 1 is made of GaAs or GaP. As shown in FIG. 4, the heterojunction portion 4 is crystal-grown between the semiconductor substrate 1 and the cladding layer 3 via a relaxation buffer layer 6 that relaxes the lattice mismatch between the two.
[0048]
In the ninth embodiment, by forming the heterojunction portion 4 on the GaAs or GaP substrate 1 via the relaxation buffer layer 6 that relaxes the lattice mismatch, the lattice mismatch is relaxed and the heterojunction portion 4 can be grown. . In addition, it is possible to continuously perform the growth continuously with the same crystal growth apparatus, and it is easy and cost-effective because only one apparatus is required.
[0049]
In the semiconductor light emitting device of the ninth embodiment, the relaxation buffer layer 6 is a graded layer whose lattice constant gradually changes from the lattice constant of the semiconductor substrate 1 in the growth direction and approaches the lattice constant of the cladding layer 3. Can be configured.
[0050]
As described above, when the graded layer is used as the relaxation buffer layer 6, lattice relaxation occurs gradually, so that threading dislocations can be prevented from growing above the graded layer, and the crystal of the heterojunction 4 can be prevented. It is not necessary to reduce the sex.
[0051]
In the semiconductor light emitting device of the ninth embodiment, the relaxation buffer layer 6 can also be configured as a strained superlattice structure in which at least two types of materials having different lattice constants are alternately stacked.
[0052]
As described above, when the strained superlattice structure is used as the relaxation buffer layer 6, crystal defects accompanying the lattice relaxation can be confined in the strained superlattice structure, and the crystallinity of the heterojunction portion 4 is prevented from being lowered. Can do.
[0053]
In the semiconductor light emitting device of the ninth embodiment, the relaxation buffer layer 6 can be configured as a low-temperature buffer layer grown at a temperature lower than the growth temperature of the cladding layer 3.
[0054]
Thus, when the low-temperature buffer layer is used as the relaxation buffer layer 6, crystal defects accompanying lattice relaxation can be confined in the low-temperature buffer layer, and the crystallinity of the heterojunction portion 4 can be prevented from being lowered. .
[0055]
In each of the above examples, GaInP or GaPAs can be used for the relaxation buffer layer 6.
[0056]
GaPAs or GaInP is a ternary material and is easy to control. In the case of using GaPAs, when the semiconductor substrate 1 is a GaP substrate, it is only necessary to add As to the GaP, and when the semiconductor substrate 1 is a GaAs substrate, it is only necessary to add P to the GaAs, which is easy to control. In addition, in the case of GaInP, P is the only group V having a high vapor pressure, so that the interface can be easily controlled particularly when growing a strained superlattice structure.
[0057]
In the semiconductor light emitting device of the eighth or ninth embodiment, the plane orientation of the semiconductor substrate 1 is a plane inclined in the range of 0 ° to 54.7 ° in the [011] direction from the (100) plane, or , A plane inclined in the range of 10 ° to 54.7 ° in the [0-11] direction from the (100) plane, or a plane equivalent to these.
[0058]
That is, the plane orientation of the semiconductor substrate 1 is inclined in the range of 0 ° to 54.7 ° from the (100) plane in the [011] direction, or [0-11] from the (100) plane. By tilting in the direction of 10 ° to 54.7 °, the formation of the natural superlattice can be suppressed, and a wide gap is formed with the same composition ratio as compared to the case where the natural superlattice is formed. This is advantageous for wavelength conversion. Further, an end face type laser usually uses a cleavage plane as a resonator. When the plane orientation of the substrate 1 is tilted in the above direction, the cleavage plane perpendicular to the tilted direction does not become perpendicular, but when the plane is cleaved in the tilted direction, a vertical plane is obtained, which can be used as a laser resonator. If it is tilted in a direction other than the above, the cleavage plane will not be vertical, which is not preferable. Further, the hillock density can be reduced by inclining the plane orientation of the substrate from the (100) plane. Thereby, deterioration of device characteristics and yield reduction can be suppressed.
[0059]
In the semiconductor light emitting device of the eighth or ninth embodiment, the GaPAs substrate surface is planarized by mechanical polishing prior to crystal growth of the heterojunction portion, or after growth of the relaxation buffer layer. The surface before the heterojunction crystal is grown should be flattened by mechanical polishing.
[0060]
On the surface of the GaPAs substrate 1 or the surface after the growth of the relaxation buffer layer 6, cross-hatched irregularities related to lattice irregularities are usually formed. This unevenness can be the origin of new crystal defects when the heterojunction 4 is grown thereon. This can be prevented by flattening by polishing and growing the heterojunction portion 4 thereon.
[0061]
Further, in the semiconductor light emitting device of the eighth or ninth embodiment, a layer in which the upper surface of the interface of the layer is flatter than the lower surface (substrate side) may be included between the semiconductor substrate 1 and the heterojunction portion 4. it can.
[0062]
That is, on the surface of the GaPAs substrate 1 or on the surface after the growth of the relaxation buffer layer 6, cross-hatched irregularities related to lattice irregularities are usually formed. This unevenness can be the origin of new crystal defects when the heterojunction 4 is grown thereon. When a layer that grows by embedding such irregularities is included, the upper layer becomes flat, and this can be prevented.
[0063]
In this case, a layer whose upper surface at the interface of the layer is flatter than the lower surface (substrate side) is Se 5 × 10 5.¹⁸cm^-3GaInP doped as described above can be used.
[0064]
That is, the inventor of the present application has found that GaInP doped with Se at a high concentration has a property of growing while embedding irregularities. Thereby, since the upper surface of the interface of the layer becomes flatter than the lower surface (substrate side), it is possible to prevent the occurrence of new crystal defects originating from irregularities when the heterojunction portion 4 is grown.
[0065]
Further, in the semiconductor light emitting device of the ninth embodiment, the relaxation buffer layer 6 has Se of 5 × 10 5.¹⁸cm^-3GaInP doped as described above is preferable.
[0066]
That is, by using GaInP doped with Se at a high concentration, which has a property of embedding the unevenness in the relaxation buffer layer 6 itself, which is the origin of generating the cross hatched unevenness related to lattice irregularity, The effect of alleviating irregularities and the effect of flattening the surface can be combined, and the total thickness of the growth layer can be reduced.
[0067]
Further, in the semiconductor light emitting device of each example described above, the heterojunction portion 4 can be grown by metal organic vapor phase epitaxy (MOCVD) or molecular beam epitaxy (MBE).
[0068]
That is, the AlGaInP (As) -based material has a large segregation coefficient of Al from the solution to the solid phase, and liquid layer growth is difficult from the viewpoint of composition control. Further, the vapor phase growth method (VPE) by the halogen transport method is difficult because AlCl as a raw material corrodes the quartz reaction tube. On the other hand, metal organic vapor phase epitaxy (MOCVD) or molecular beam epitaxy (MBE) is a highly non-equilibrium growth method, and growth is based on the Group III material supply rule. Is extremely effective and can grow easily.
[0069]
The relaxation buffer layer 6 can also be grown by metal organic vapor phase epitaxy (MOCVD) or molecular beam epitaxy (MBE).
[0070]
In this case, growth can be continuously performed using the same apparatus as the crystal growth apparatus for the heterojunction portion, and since only one apparatus is required, it is easy and has an advantage in cost.
[0071]
【Example】
Examples according to the present invention will be described below. In the following Examples 1 to 7, the basic configuration of the semiconductor light emitting element (semiconductor laser element) is as shown in FIG. That is, the materials, compositions, and the like are different for each example, but the basic configuration of each example is that of FIG. Therefore, in the first to seventh embodiments, for convenience, the semiconductor light emitting devices of the first to seventh embodiments will be described as having the basic configuration shown in FIG. Note that the semiconductor light emitting device of FIG. 5 has a SCH-SQW structure as a layer structure.
[0072]
Example 1
In Example 1, first, the Ga composition is gradually changed from 0.5 to 0.7 by MOCVD on the GaAs substrate 11 which is 15 ° off from the (100) plane in the [011] direction.¹⁸cm^-3The n-GaInP graded buffer layer 12 having a thickness of 2 μm doped as described above is stacked, and Se is formed as a surface flattening layer thereon with 5 × 10 5.¹⁸cm^-3N-Ga doped above_0.7In_0.3A composition uniform layer 13 made of P and having a thickness of 1 μm is grown to alleviate the lattice mismatch. By doping Se, cross-hatched irregularities associated with lattice relaxation were reduced. According to experiments, Se has a high concentration (5 × 10¹⁸cm³It was found that GaInP doped to the above has a property of growing with embedding irregularities. That is, n-Ga doped with Se_0.7In_0.3The upper surface of the interface of the P composition uniform layer 13 was flatter than the lower surface (substrate side). When a heterojunction was grown on a non-planar surface, new crystal defects originated from the irregularities were generated, but this could be prevented by flattening. Since Se was added to the graded layer at a high concentration, the effect of surface flattening was obtained, and the surface flattened layer could be thinned.
[0073]
Next, the lattice constant between GaP and GaAs, Ga_0.7In_0.3N- (Al equal to the lattice constant of P_yGa_1-y)_βIn_1-βP_vAs_1-v(Y = 1, β = 0.7, v = 1) cladding layer 14 (film thickness is 1 μm), (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0.1, γ = 0.7, u = 1) Light guide layer 15 (film thickness is 0.1 μm), having compressive strain (Al_xGa_1-x)_αIn_1-αP_tAs_1-t(x = 0, α = 0.6, t = 1) Single quantum well active layer 16 (film thickness is 8 nm), (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0.1, γ = 0.7, u = 1) Light guide layer 17 (film thickness is 0.1 μm), p- (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(y = 1, β = 0.7, v = 1) Clad layer 18 (film thickness is 1 μm), p-Ga_0.7In_0.3A P cap layer 19 (with a film thickness of 0.1 μm) and a p-GaAs contact layer 20 (with a film thickness of 0.005 μm) were grown. Here, the cladding layers 14 and 18 and the guide layers 15 and 17 are made of Ga._0.7In_0.3It is lattice-matched to the P composition uniform layer 13.
[0074]
On the contact layer 20, SiO as the insulating film 21 is formed.₂And a p-side electrode 22 are formed, and an n-side electrode 23 is formed on the back surface of the substrate 11. This semiconductor light emitting device is configured as an insulating film stripe structure, but other structures can also be used.
[0075]
In the first embodiment, the clad layers 14 and 18 and the light guide layers 15 and 17 have a wider gap than a conventional material system lattice-matched to a GaAs substrate. With this structure, a semiconductor laser that oscillates at a wavelength of 595 nm shorter than 600 nm Obtained. Even though the wavelength is shorter than 600 nm, the Al composition can be reduced as compared with a light guide layer used for a conventional 635 nm band laser or the like on a GaAs substrate. For this reason, the non-radiative recombination current resulting from Al was reduced, and the luminous efficiency was improved. Further, the surface recombination current is reduced, the level of end face light degradation is increased, and a high output can be obtained. Further, in Example 1, GaInP is used for the quantum well active layer 16. In GaInP, when the Ga composition is decreased, the lattice constant increases and the band gap decreases. Referring to the estimation of band discontinuity by Sandip et al. (Appl. Phys. Lett. 60, 1992, pp 630 to 632), the band gap changes mainly on the conduction band side, and the energy on the valence band side changes little. Not done. That is, even if the composition is changed, the change in energy of the valence band is small. On the other hand, when Al is added to GaInP, the conduction band energy increases and the valence band energy decreases. The change is larger on the valence band side. Conventionally, in a structure on a GaAs substrate, AlGaInP having a large Al composition has to be used as a light guide layer, and has a large band discontinuity on the valence band side with the GaInP quantum well layer. That is, the band on the conduction band side was not sufficiently large. According to the present invention, since the Al composition of the light guide layers 15 and 17 can be reduced, a large conduction band discontinuity can be obtained. As a result, carrier (electron) overflow due to the small band discontinuity on the conduction band side, which has been a problem with conventional red lasers using AlGaInP materials, can be remarkably improved, and the temperature characteristics are good at a low threshold.
[0076]
In Example 1, the composition of the cladding layers 14 and 18 has a band gap larger than that of the active layer 16 and contains Al (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1) can be used. The optical guide layers 15 and 17 have a band gap smaller than that of the cladding layers 14 and 18 and larger than that of the active layer 16 and have the same lattice constant as that of the cladding layers 14 and 18 (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(0 ≦ z <1, 0.5 <γ <1, 0 <u ≦ 1) can be used. In Example 1, the active layer 16 is a single quantum well active layer, but may be a multiple quantum well. Further, although the lattice constant varies depending on the value of β of the cladding layers 14 and 18, this can be dealt with by changing the lattice constant of the uppermost surface of the relaxation buffer layers (12 and 13) to be the same as that of the cladding layers 14 and 18.
[0077]
The plane orientation of the GaAs substrate is in the range of 0 ° to 54.7 ° in the [011] direction from the (100) plane, or in the range of 10 ° to 54.7 ° in the [011] direction from the (100) plane. If it is inclined, the formation of the natural superlattice can be suppressed, so that the reduction of the band gap can be prevented, which is advantageous for shortening the wavelength. Further, the end face type laser usually uses a cleavage plane as a resonator. When the surface orientation of the substrate 11 is tilted in the above direction, the cleavage plane perpendicular to the tilted direction does not become perpendicular, but when the surface is cleaved in the tilted direction, a vertical plane is obtained and a laser resonator can be obtained. If it is tilted in a direction other than the above, the cleavage plane will not be vertical, which is not preferable. Further, by tilting the plane orientation of the substrate from the (100) plane, the hillock density can be reduced, and thereby deterioration of device characteristics and yield can be suppressed. In the first embodiment, the lattice relaxation buffer layers 12 and 13 and the heterojunction are grown at a time by the MOCVD method. Since only one apparatus is required, there is a merit and cost advantage. The structure of FIG. 5 can also be grown by MBE (molecular beam epitaxy). An AlGaInP (As) material that is a heterojunction has a large segregation coefficient of Al from a solution to a solid phase, so that liquid layer growth is difficult from the viewpoint of composition control. Further, the vapor phase growth method (VPE) by the halogen transport method is difficult because AlCl as a raw material corrodes the quartz reaction tube. On the other hand, metal organic vapor phase epitaxy (MOCVD) or molecular beam epitaxy (MBE) is a highly non-equilibrium growth method, and growth is based on the Group III material supply rule. Is extremely effective and can grow easily. In the first embodiment, the semiconductor laser is described, but the present invention can also be applied to a light emitting diode.
[0078]
Example 2
The second embodiment is an application example to a red laser of 635 nm, 650 nm, etc. by an As-containing quantum well active layer. That is, in Example 2, the quantum well active layer contains As. In Example 2, first, the Ga composition is gradually changed from 0.5 to 0.7 by MOCVD on the GaAs substrate 11 which is 15 ° off from the (100) plane in the [011] direction, and Se is 5 ×. 10¹⁸cm^-3The n-GaInP graded buffer layer 12 having a thickness of 2 μm doped as described above is laminated, and Se is added 5 × 10 5 thereon.¹⁸cm^-3N-Ga doped above_0.7In_0.3A composition uniform layer 13 made of P and having a thickness of 1 μm is grown to alleviate the lattice mismatch. By doping Se at a high concentration, cross-hatched irregularities associated with lattice relaxation were reduced. That is, n-Ga doped with Se_0.7In_0.3The upper surface of the interface of the P composition uniform layer 13 was flatter than the lower surface (substrate side). As a result, it is possible to prevent the occurrence of new crystal defects originating from irregularities when the heterojunction portion is grown.
[0079]
Next, the lattice constant between GaP and GaAs, Ga_0.7In_0.3N- (Al equal to the lattice constant of P_yGa_1-y)_βIn_1-βP_vAs_1-v(y = 0.7, β = 0.7, v = 1) Clad layer 14 (film thickness is 1 μm), (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0.1, γ = 0.7, u = 1) The light guide layer 15 (with a film thickness of 0.1 μm) and As having compressive strain are included (Al_xGa_1-x)_αIn_1-αP_tAs_1-t(x = 0, α = 0.6, t = 0.9) Single quantum well active layer 16 (film thickness is 8 nm), (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0.1, γ = 0.7, u = 1) Light guide layer 17 (film thickness is 0.1 μm), p- (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(y = 0.7, β = 0.7, v = 1) Clad layer 18 (film thickness is 1 μm), p-Ga_0.7In_0.3A P cap layer 19 (with a film thickness of 0.1 μm) and a p-GaAs contact layer 20 (with a film thickness of 0.005 μm) are grown. The cladding layers 14 and 18 and the light guide layers 15 and 17 are made of Ga._0.7In_0.3P is lattice matched.
[0080]
On the contact layer 20, SiO as the insulating film 21 is formed.₂And a p-side electrode 22 are formed, and an n-side electrode 23 is formed on the back surface of the substrate 11. This semiconductor light emitting device is configured as an insulating film stripe structure, but other structures can also be used.
[0081]
In the lattice constants of the cladding layers 14 and 18 of Example 2, even when GaInP having a small band gap is used in AlGaInP, the strain greatly exceeds 1% to obtain 635 nm, and the crystallinity is lowered. As was added to 16 to adjust the band gap. Of course, it is not necessary to add As if the structure (composition) can provide the necessary wavelength.
[0082]
With the structure of Example 2, a semiconductor laser oscillating at a wavelength of 635 nm was obtained. Further, since the compression strain quantum well active layer 16 is used, the polarization is TE mode. Many lasers in other wavelength bands are convenient for application because they are TE modes. Of course, if the well layer is a direct transition material, a tensile strain quantum well active layer may be used. In order to use a tensile strain quantum well layer that is a direct transition, it is desirable to make the lattice constant of the cladding layer larger than that of the second embodiment. The clad layers 14 and 18 and the light guide layers 15 and 17 have a wider gap than the conventional material system lattice-matched to the GaAs substrate, and as a result of increased band discontinuity, carrier confinement is improved. In addition to the effects of compressive strain and quantum well, a wide gap material can be used as the compressive strain quantum well layer. Therefore, a compressive strain quantum well layer using a clad layer having a lattice constant on a conventional GaAs substrate is used. Compared with, the well width became thicker, and the adverse effect of the interface was reduced. In addition, the Al composition included in the group III of the light guide layer is 0.07, which can be reduced as compared with the prior art, non-radiative recombination current caused by Al is reduced, and luminous efficiency is improved. In addition, the surface recombination current is reduced, the level of end face light degradation is improved, and high output can be obtained.
[0083]
Further, the composition of the cladding layers 14 and 18 has a band gap larger than that of the active layer 16 and contains Al (Al_yGa_1-y)_βIn_1-βP_vAs_1-v (0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1) can be used. The light guide layers 15 and 17 have a band gap smaller than that of the cladding layers 14 and 18 and larger than that of the active layer 16 and have the same lattice constant as that of the cladding layer (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(0 ≦ z <1, 0.5 <γ <1, 0 <u ≦ 1) can be used. In Example 2, a single quantum well active layer is used, but a multiple quantum well may be used. Further, although the lattice constant varies depending on the β value of the cladding layers 14 and 18, this can be dealt with by changing the lattice constant of the uppermost surface of the lattice relaxation buffer layer to be the same as that of the cladding layers 14 and 18.
[0084]
Further, as in Example 2, the plane orientation of the GaAs substrate 11 is in the range of 0 ° to 54.7 ° from the (100) plane to the [011] direction, or 10 ° from the (100) plane to the [011] direction. If it is inclined within the range of 54.7 °, the formation of the natural superlattice can be suppressed, so that the reduction of the band gap can be prevented, which is advantageous for shortening the wavelength. In the above example, the lattice relaxation buffer layers 12 and 13 and the heterojunction are grown by the MOCVD method, but can also be grown by the MBE method (molecular beam epitaxy).
[0085]
Example 3
The difference between the third embodiment and the second embodiment is the material of the lattice relaxation buffer layer 12. That is, in Example 3, a film doped with Se by gradually changing the P composition from 0 to 0.4 by the MOCVD method on the GaAs substrate 11 which is 15 ° off from the (100) plane in the [011] direction. An n-GaP layer in which an n-GaPAs graded lattice relaxation buffer layer 12 having a thickness of 2 μm is stacked and Se is doped thereon._0.4As_0.6A uniform composition layer 13 having a film thickness of 1 μm was grown to alleviate the lattice mismatch. That is, in Example 1 and Example 2, GaInP is used for the lattice relaxation buffer layer, but in Example 3, GaPAs is used for the lattice relaxation buffer layer. Others are the same as in the second embodiment. In Example 3, the same effect as in Example 2 was obtained.
[0086]
Example 4
The difference between the fourth embodiment and the second embodiment is the structure of the lattice relaxation buffer layer 12. That is, in Example 4, the GaCVD lattice-matched to the GaAs substrate 11 as shown in FIG. 6 on the GaAs substrate 11 off by 15 ° in the [011] direction from the (100) plane, as shown in FIG._0.5In_0.5Ga which is the same as the lattice constant of P and the cladding layer 14_0.7In_0.3Se composed of P is 5 × 10¹⁸cm^-3A lattice relaxation buffer layer (n-GaInP / GaInP superlattice buffer layer) 12 composed of the n-strained superlattice doped as described above and having a film thickness of 2 μm is stacked, and Se is deposited thereon by 5 × 10 6.¹⁸cm^-3N-Ga doped above_0.7In_0.3A 1 μm uniform composition layer 13 made of P was grown to relax the lattice mismatch. Others are the same as in the second embodiment. In Example 4, the same effect as in Example 2 was obtained.
[0087]
Example 5
The difference between the fifth embodiment and the second embodiment is the structure of the lattice relaxation buffer layer 12. That is, in Example 5, GaP which is the same as the lattice constant of the cladding layer 14 is formed on the GaAs substrate 11 which is 15 ° off from the (100) plane in the [011] direction by MOCVD._0.4As_0.6An n-low-temperature lattice relaxation buffer layer (n-GaPAs low-temperature buffer layer) 12 having a thickness of 0.1 μm grown at a lower temperature than the clad layer 14 made of is laminated, and Se is 5 × 10 5 thereon.¹⁸cm^-3N-Ga doped above_0.7In_0.3A uniform composition layer 13 made of P and having a thickness of 2 μm was grown to alleviate the lattice mismatch. Others are the same as in the second embodiment. In Example 5, the same effect as in Example 2 was obtained.
[0088]
Example 6
Example 6 is an application example to a red laser of 635 nm, 650 nm, or the like using a light guide layer that does not contain Al. In Example 6, first, the Ga composition is gradually changed from 0.5 to 0.7 by MOCVD on the GaAs substrate 11 which is 15 ° off from the (100) plane in the [011] direction, and Se is 5 ×. 10¹⁸cm^-3The n-GaInP graded buffer layer 12 having a thickness of 2 μm doped as described above is laminated, and Se is added 5 × 10 5 thereon.¹⁸cm^-3N-Ga doped above_0.7In_0.3A composition uniform layer 13 made of P and having a thickness of 1 μm is grown to alleviate the lattice mismatch. By doping Se at a high concentration, cross-hatched irregularities due to lattice relaxation were reduced. That is, n-Ga doped with Se_0.7In_0.3The upper surface of the interface of the P composition uniform layer 13 was flatter than the lower surface (substrate side). As a result, it is possible to prevent the occurrence of new crystal defects originating from the unevenness when the heterojunction is grown.
[0089]
Next, the lattice constant between GaP and GaAs, Ga_0.7In_0.3N- (Al equal to the lattice constant of P_yGa_1-y)_βIn_1-βP_vAs_1-v(y = 0.7, β = 0.7, v = 1) Cladding layer 14 (film thickness is 1 μm), does not contain Al (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0, γ = 0.7, u = 1) Light guide layer 15 (film thickness is 0.1 μm), and has compressive strain as shown in FIG._xGa_1-x)_αIn_1-αP_tAs_1-t(x = 0, α = 1, t = 0.3) well layer (film thickness is 8 nm) and no Al (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0, γ = 0.7, u = 1) Multi-quantum well active layer 16 in which three barrier layers (thickness: 10 nm) are alternately stacked, does not contain Al (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0, γ = 0.7, u = 1) Light guide layer 17 (film thickness is 0.1 μm), p- (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(y = 0.7, β = 0.7, v = 1) Clad layer 18 (film thickness is 1 μm), p-Ga_0.7In_0.3A P cap layer 19 (film thickness is 0.1 μm) and a p-GaAs contact layer 20 (film thickness is 0.005 μm) are grown. The cladding layers 14 and 18 and the light guide layers 15 and 17 are made of Ga._0.7In_0.3P is lattice matched.
[0090]
On the contact layer 20, SiO as the insulating film 21 is formed.₂And a p-side electrode 22 are formed, and an n-side electrode 23 is formed on the back surface of the substrate 11. This semiconductor light emitting device is configured as an insulating film stripe structure, but other structures can also be used.
[0091]
In the lattice constants of the cladding layers 14 and 18 of Example 6, even if GaInP having a small band gap is used in AlGaInP, the strain must be increased to obtain 650 nm, and the crystallinity is lowered. The band gap was adjusted by adding As to the layer 16. GaInP also has a smaller lattice constant and a smaller band gap as the Ga composition is decreased. Referring to the estimation of band discontinuity by Sandip et al. (Appl. Phys. Lett. 60, 1992, pp 630-632), the band gap changes on the conduction band side and the energy on the valence band side hardly changes. . That is, when a heterojunction is formed between an Al-free wide gap GaInP light guide layer and a compression strained GaInP quantum well layer having a larger lattice constant, the band discontinuity is almost only on the conduction band side. As a result, carrier (electron) overflow due to a small band discontinuity on the conduction band side, which has been a problem with conventional red lasers using AlGaInP materials, can be significantly improved. However, conversely, there is a concern that hole confinement worsens on the valence band side. Here, when As is added to GaInP, the band gap is reduced. However, since the change on the valence band side is larger, there is an effect of realizing a structure in which holes can be sufficiently confined.
[0092]
With the structure of Example 6, a semiconductor laser oscillating at a wavelength of 650 nm was obtained. Polarization was in TE mode. The clad layers 14 and 18 and the light guide layers 15 and 17 have a wider gap than a conventional material system lattice-matched to a GaAs substrate, and as a result, the band discontinuity is increased. In Example 6, since the multiple quantum well structure is used, carriers can be more sufficiently confined in the well layer. In addition to the effects of compressive strain and quantum well, a wide gap material can be used as the compressive strain quantum well layer. Compared to a conventional compressive strain well layer using a clad layer lattice-matched to a GaAs substrate. As a result, the well width was increased, and the adverse effect of the interface was reduced. Further, since the light guide layers 15 and 17 and the well layer 16 have a structure containing no Al, the non-light-emitting recombination current caused by Al is reduced, and the light emission efficiency is improved. In addition, the surface recombination current is reduced, the level of end face light degradation is greatly improved, and high output can be obtained. For this reason, a red laser capable of stable operation at high temperature and high output was obtained.
[0093]
The cladding layers 14 and 18 have a larger band gap than the active layer 16 and contain Al (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1) can be used. Further, although the lattice constant varies depending on the β value of the cladding layers 14 and 18, it can be dealt with by changing the lattice constant of the uppermost surface of the lattice relaxation buffer layer 12 to be the same as that of the cladding layer 14. In Example 6, the barrier layer having the same lattice constant as that of the cladding layers 14 and 18 is used as the barrier layer. However, when the strain of the well layer is large, the strain composition is set, and the direction of the strain is opposite to the well layer. By so doing, it is possible to compensate for the distortion of the well layer and obtain a good quantum well structure.
[0094]
Further, as in Example 6, the plane orientation of the GaAs substrate 11 is in the range of 0 ° to 54.7 ° from the (100) plane to the [011] direction, or 10 from the (100) plane to the [011] direction. If the angle is in the range of 5 ° to 54.7 °, formation of a natural superlattice can be suppressed, so that the reduction of the band gap can be prevented, and the clad layers 14 and 18 and the light guide layers 15 and 17 can be formed with the same composition. A wide gap is preferable. In Example 6, the lattice relaxation buffer layers 12 and 13 and the heterojunction are grown by the MOCVD method, but can also be grown by the MBE method (molecular beam epitaxy).
[0095]
Example 7
Example 7 is an application example to a red laser of 635 nm, 650 nm, or the like by a light guide layer not containing Al. In Example 7, the Ga composition is first gradually changed from 1 to 0.78 by MOCVD on the GaP substrate 11 which is 15 ° off in the [011] direction from the (100) plane, and Se is 5 × 10 6.¹⁸cm^-3The n-GaInP graded buffer layer 12 having a thickness of 2 μm doped as described above is laminated, and Se is added 5 × 10 5 thereon.¹⁸cm^-3N-Ga doped above_0.78In_0.22A composition uniform layer 13 made of P and having a thickness of 1 μm is grown to alleviate the lattice mismatch. By doping Se at a high concentration, cross-hatched irregularities associated with lattice relaxation were reduced. That is, n-Ga doped with Se_0.78In_0.22The upper surface of the interface of the P composition uniform layer was flatter than the lower surface (substrate side). As a result, it is possible to prevent the occurrence of new crystal defects originating from irregularities when the heterojunction portion is grown. Next, the lattice constant between GaP and GaAs, Ga_0.78In_0.22N- (Al equal to the lattice constant of P_yGa_1-y)_βIn_1-βP_vAs_1-v(y = 0.7, β = 0.78, v = 1) Cladding layer 14 (film thickness is 1 μm), does not contain Al (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0, γ = 0.78, u = 1) Light guide layer 15 (film thickness is 0.1 μm), and has compressive strain as shown in FIG._xGa_1-x)_αIn_1-αP_tAs_1-t(x = 0, α = 1, t = 0.3) Compression strain quantum well layer 16 (film thickness is 8 nm) and no Al (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0, γ = 0.78, u = 1) Multiple quantum well active layers 16 in which barrier layers (thickness is 10 nm) are alternately stacked in three layers, do not contain Al (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0, γ = 0.78, u = 1) Light guide layer 17 (film thickness is 0.1 μm), p- (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(y = 0.7, β = 0.78, v = 1) Clad layer 18 (film thickness is 1 μm), p-Ga_0.7In_0.3A P cap layer 19 (film thickness is 0.1 μm) and a p-GaP contact layer 20 (film thickness is 0.005 μm) are grown. The cladding layers 14 and 18 and the light guide layers 15 and 17 are made of Ga._0.78In_0.22P is lattice matched.
[0096]
On the contact layer 20, SiO as the insulating film 21 is formed.₂And a p-side electrode 22 are formed, and an n-side electrode 23 is formed on the back surface of the substrate 11. This semiconductor light emitting device is configured as an insulating film stripe structure, but other structures can also be used.
[0097]
With the lattice constants of the cladding layers 14 and 18 of Example 7, the strain must be increased to obtain 635 nm even if GaInP having a small band gap is used in AlGaInP, and the crystallinity is lowered. In 16, the band gap was adjusted by adding As.
[0098]
With the structure of Example 7, a semiconductor laser oscillating at a wavelength of 635 nm was obtained. Polarization was in TE mode. The clad layers 14 and 18 and the light guide layers 15 and 17 have a wider gap than the conventional material system lattice-matched to the GaAs substrate, and carrier confinement is improved. In addition to the effects of compressive strain and quantum well, a wide gap material can be used as the compressive strain quantum well layer. Compared to a conventional compressive strain well layer using a clad layer lattice-matched to a GaAs substrate. As a result, the well width was increased, and the adverse effect of the interface was reduced. In addition, since the light guide layers 15 and 17 and the well layer 16 have a structure containing no Al, the non-radiative recombination current caused by Al is reduced and the light emission efficiency is improved. In addition, the surface recombination current is reduced, the level of end face light degradation is greatly improved, and a high output can be obtained. For this reason, a red laser capable of stable operation at high temperature and high output was obtained.
[0099]
The compositions of the cladding layers 14 and 18 have a larger band gap than the active layer 16 and contain Al (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1) can be used. Further, although the lattice constant varies depending on the value of β of the cladding layers 14 and 18, this can be dealt with by changing the lattice constant of the uppermost surface of the lattice relaxation buffer layers 12 and 13 to be the same as that of the cladding layer 14.
[0100]
Further, as in Example 7, the plane orientation of the GaAs substrate 11 is in the range of 0 ° to 54.7 ° in the [011] direction from the (100) plane, or 10 in the [011] direction from the (100) plane. If the angle is in the range of 5 ° to 54.7 °, the formation of the natural superlattice can be suppressed, so that the reduction of the band gap can be prevented. Even with the same composition, the cladding layers 14 and 18 and the light guide layers 15 and 17 A wide gap is preferable. In Example 7, the lattice relaxation buffer layers 12 and 13 and the heterojunction are grown by the MOCVD method, but can also be grown by the MBE method (molecular beam epitaxy).
[0101]
Example 8
FIG. 8 is a diagram showing a semiconductor light emitting device (semiconductor laser device) of Example 8. The layer structure is an SCH-SQW structure. Example 8 is an example using a GaPAs substrate. That is, in Example 8, GaPAs in which the P composition was gradually changed from 0 to 0.4 on the GaAs substrate 31 off by 15 ° in the [011] direction from the (100) plane by the VPE method (vapor phase growth). A graded layer 32 is laminated with a thickness of 30 μm, and GaP is formed thereon._0.4As_0.6A uniform composition layer 33 is grown to a thickness of 20 μm, and a GaPAs substrate 34 having a growth layer thickness of 50 μm, for example, is used. Here, the GaPAs substrate 34 is an epitaxial substrate grown to a thickness of, for example, 30 μm or more on a GaAs or GaP substrate by VPE or the like. The surface of the growth layer has a sufficiently relaxed lattice mismatch and can be said to be a GaPAs substrate.
[0102]
In Example 8, next, n-Ga doped with Se by MOCVD method._0.7In_0.3A P buffer layer 35 (having a film thickness of 1 μm) is grown to flatten the surface. Next, the lattice constant between GaP and GaAs, GaP_0.4As_0.6N- (Al equal to the lattice constant of_yGa_1-y)_βIn_1-βP_vAs_1-v(y = 0.7, β = 0.7, v = 1) cladding layer 36 (film thickness is 1 μm), (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0.1, γ = 0.7, u = 1) Light guide layer 37 (film thickness is 0.1 μm), having compressive strain (Al_xGa_1-x)_αIn_1-αP_tAs_1-t(x = 0, α = 0.55, t = 1) Single quantum well active layer 38 (film thickness is 8 nm), (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0.1, γ = 0.7, u = 1) Light guide layer 39 (film thickness is 0.1 μm), p- (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(y = 0.7, β = 0.7, v = 1) Clad layer 40 (film thickness is 1 μm), p-Ga_0.7In_0.3A P cap layer 41 (with a film thickness of 0.1 μm) and a p-GaAs contact layer 42 (with a film thickness of 0.05 μm) are grown. The clad layers 36 and 40 and the light guide layers 37 and 39 are lattice-matched to the GaPAs substrate 34. On the contact layer 42, SiO as the insulating film 43 is formed.₂And a p-side electrode 44 are formed, and an n-side electrode 45 is formed on the back surface of the substrate 31. This semiconductor light emitting device is configured as an insulating film stripe structure, but other structures can also be used.
[0103]
With the structure of Example 8, a semiconductor laser that oscillates at a wavelength of 635 nm was obtained. Polarization was in TE mode. The clad layers 36 and 40 and the light guide layers 37 and 39 have a wider gap than the conventional material system lattice-matched to the GaAs substrate, and carrier confinement is improved. In addition to the effects of compressive strain and quantum well, a wide gap material can be used as the compressive strain quantum well layer. Compared to conventional compressive strain well layers using a clad layer lattice-matched to a GaAs substrate. The well width became thicker and the adverse effect of the interface was reduced. Further, the Al composition of the light guide layer has been reduced compared to the prior art, and the light output level at which the end face light deteriorates has increased. As a result, a laser capable of stable operation at high temperature and high output was obtained.
[0104]
The composition of the cladding layers 36 and 40 has a larger band gap than the active layer 38 and contains Al (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1) can be used. The optical guide layers 37 and 39 have a band gap smaller than that of the cladding layer and larger than that of the active layer, and have the same lattice constant as that of the cladding layer (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(0 ≦ z <1, 0.5 <γ <1, 0 <u ≦ 1) can be used. In Example 8, a multiple quantum well using a single quantum well active layer may be used. Further, although the lattice constant varies depending on the value of β of the cladding layers 36 and 40, it can be dealt with by changing the lattice constant of the uppermost surface of the GaPAs substrate 34 to be the same as that of the cladding layers 36 and 40. Further, as in Example 8, the plane orientation of the GaAs substrate ranges from 0 ° to 54.7 ° in the [011] direction from the (100) plane, or 10 ° in the [011] direction from the (100) plane. If it is inclined within the range of 54.7 °, formation of a natural superlattice can be suppressed, so that the reduction of the band gap can be prevented, and even with the same composition, the clad layer and the light guide layer have a wide gap, which is preferable. .
[0105]
Example 9
FIG. 9 is a diagram showing a semiconductor light emitting device (semiconductor laser device) of Example 9. Example 9 is an application example to a red laser of 635 nm, 650 nm, etc. by a light guide layer not containing Al. The layer structure is an SCH-MQW structure. In Example 9, first, the P composition was gradually changed from 1 to 0.55 by the VPE method (vapor phase growth) on the GaP substrate 51 which was turned off by 15 ° in the [011] direction from the (100) plane. A GaPAs graded layer 52 is laminated with a film thickness of 30 μm, and GaPs are formed thereon._0.55As_0.45A uniform composition layer 53 made of a material is grown to a thickness of 20 μm, and a GaPAs substrate 54 having a thickness of the grown layer of 50 μm, for example, is used.
[0106]
In Example 9, before the crystal growth of the heterojunction portion, the surface of the GaPAs substrate 54 having the cross-hatched irregularities on the surface was planarized (wrapped interface) by mechanical polishing. Further, in order to remove damage due to polishing, the surface was removed by slightly etching with a chemical solution. As a result, it is possible to prevent the occurrence of new crystal defects when a heterojunction portion having unevenness is grown.
[0107]
Next, n-Ga is formed by MOCVD._0.78In_0.22A buffer layer 55 made of P having a thickness of 0.3 μm, a lattice constant between GaP and GaAs, and Ga_0.78In_0.22N- (Al equal to the lattice constant of P_yGa_1-y)_βIn_1-βP_vAs_1-v(Y = 0.7, β = 0.78, v = 1) Clad layer 56 (film thickness is 1 μm), does not contain Al (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0, γ = 0.78, u = 1) Light guide layer 57 (film thickness is 0.1 μm), having compressive strain (Al_xGa_1-x)_αIn_1-αP_tAs_1-t(x = 0, α = 1, t = 0.3) (film thickness is 8 nm) and does not contain Al (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0, γ = 0.78, u = 1) Multiple quantum well active layer 58 in which barrier layers (film thickness is 10 μm) are alternately stacked in three layers, and does not contain Al (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0, γ = 0.78, u = 1) Light guide layer 59 (film thickness is 0.1 μm), p- (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(y = 0.7, β = 0.78, v = 1) Clad layer 60 (film thickness is 1 μm), p-Ga_0.7In_0.3A P cap layer 61 (film thickness is 0.1 μm) and a p-GaP contact layer 62 (film thickness is 0.005 μm) are grown. The cladding layers 56 and 60 and the guide layers 57 and 59 are made of Ga._0.78In_0.22P is lattice matched.
[0108]
On the contact layer 62, SiO as an insulating film 63 is formed.₂And a p-side electrode 64 are formed, and an n-side electrode 65 is formed on the back surface of the substrate 51. This semiconductor light emitting device is configured as an insulating film stripe structure, but other structures can also be used.
[0109]
With the lattice constants of the clad layers 56 and 60 of Example 9, even if GaInP having a small band gap is used in AlGaInP, the strain must be increased to obtain 635 nm, and there is a concern about the decrease in crystallinity. In the well layer 58, As was added to adjust the band gap.
[0110]
With the structure of Example 9, a semiconductor laser oscillating at a wavelength of 635 nm was obtained. Polarization was in TE mode. The clad layers 56 and 60 and the light guide layers 57 and 59 have a wider gap than the conventional material system lattice-matched to the GaAs substrate, and carrier confinement is improved. In addition to the effects of compressive strain and quantum well, a wide gap material can be used as the compressive strain quantum well layer, so that the well is better than a compressive strain well layer using a clad layer lattice-matched to a conventional GaAs substrate. The width was increased and the adverse effects of the interface were reduced. Further, since the light guide layers 57 and 59 and the well layer 58 have a structure containing no Al, the non-light-emitting recombination current caused by Al is reduced, and the light emission efficiency is improved. In addition, the surface recombination current is reduced, the level of end face light degradation is improved, and high output can be obtained. For this reason, a red laser capable of stable operation at high temperature and high output was obtained.
[0111]
The clad layers 56 and 60 have a larger band gap than the active layer 58 and contain Al (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1) can be used. Further, although the lattice constant varies depending on the β value of the cladding layers 56 and 60, it can be dealt with by changing the lattice constant of the uppermost surface of the lattice relaxation buffer layer to be the same as that of the cladding layer.
[0112]
Further, as in Example 9, the plane orientation of the GaPAs substrate ranges from 0 ° to 54.7 ° in the [011] direction from the (100) plane, or from 10 ° in the [011] direction from the (100) plane. Inclination in the range of 54.7 ° can suppress the formation of the natural superlattice, which can prevent the reduction of the band gap and is preferable because the clad layer and the light guide layer have a wide gap even with the same composition. In Example 9, the heterojunction was grown by MOCVD, but it can also be grown by MBE (molecular beam epitaxy).
[0113]
Example 10
FIG. 10 is a diagram showing a semiconductor light emitting device (semiconductor laser device) of Example 10. Example 10 also has a SCH-SQW structure as a layer structure. In Example 10, first, GaP off by 2 ° in the [110] direction from the (100) plane._0.4As_0.6On the substrate 71, a GaPAs graded layer 72 having a P composition gradually changed from 0 to 0.4 is laminated by a VPE method (vapor phase growth) with a film thickness of 30 μm, and GaPs are formed thereon._0.4As_0.6A uniform composition layer 73 composed of 20 μm is grown, and a GaPAs substrate 74 having a growth layer thickness of 50 μm, for example, is used. Here, the GaPAs substrate is an epitaxial substrate grown to a thickness of, for example, 30 μm or more on a GaAs or GaP substrate by the VPE method or the like. The surface of the growth layer has a sufficiently relaxed lattice mismatch and can be said to be a GaPAs substrate.
[0114]
Next, n-GaP is formed by MOCVD._0.4As_0.6Buffer layer 75 (film thickness is 1 μm), a lattice constant between GaP and GaAs, GaP_0.4As_0.6N- (Al containing As equal to the lattice constant of_yGa_1-y)_βIn_1-βP_vAs_1-v(Y = 0.5, β = 0.8, v = 0.85) cladding layer 76 (film thickness is 1 μm), (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0, γ = 0.7, u = 1) Light guide layer 77 (film thickness is 0.1 μm), having compressive strain (Al_xGa_1-x)_αIn_1-αP_tAs_1-t(x = 0, α = 0.65, t = 0.9) Single quantum well active layer 78 (film thickness is 25 nm), (Al_zGa_1-z)_γIn_1-γP_uAs_1-u(z = 0, γ = 0.7, u = 1) Light guide layer 79 (film thickness is 0.1 μm), p- (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(y = 0.5, β = 0.8, v = 0.85) Clad layer 80 (film thickness is 1 μm), p-Ga_0.7In_0.3P cap layer 81 (film thickness is 0.1 μm), p-GaP_0.4As_0.6A contact layer 82 (film thickness is 0.2 μm) is grown. The clad layers 76 and 80 and the light guide layers 77 and 79 are lattice-matched to the GaPAs substrate 74.
[0115]
On the contact layer 82, SiO as the insulating film 83 is formed.₂And a p-side electrode 84 are formed, and an n-side electrode 85 is formed on the back surface of the substrate 71. This semiconductor light emitting device is configured as an insulating film stripe structure, but other structures can also be used.
[0116]
With the structure of Example 10, a semiconductor laser oscillating at a wavelength of 660 nm was obtained.
[0117]
In Example 10, GaP_0.4As_0.6The plane orientation of the substrate 71 is off by 2 ° in the [110] direction from the (100) plane, and has a slight inclination. Gap, GaAs, GaP with a small inclination from such (100) plane or (100)_0.4As_0.6When AlGaInP was grown on the substrate by MOCVD, many hillocks were observed on the growth surface. This hillock was particularly remarkable when compared with GaInP when the Al composition was large, such as AlInP. If a large number of hillocks are present in the growth layer, the device characteristics such as laser and LED are deteriorated and the yield is lowered, which is not preferable in production. In particular, in the laser as in Example 10, since the clad layers 76 and 80 are thick, the influence is great. The inventors of the present application have found that hillock density can be reduced by including As during AlGaInP growth. This is presumably because the formation of Al or Ga droplets is suppressed. As a result, it was possible to suppress deterioration of device characteristics and yield reduction. In addition, since the light guide layers 77 and 79 and the well layer 78 have a structure not containing Al, the non-light-emitting recombination current caused by Al is reduced, and the light emission efficiency is improved. In addition, the surface recombination current is reduced, the level of end face light degradation is greatly improved, and high output can be obtained. For this reason, a red laser capable of stable operation at high temperature and high output was obtained.
[0118]
In Example 10, a single quantum well active layer was used, but a multiple quantum well may be used. In that case, (Al_x2Ga_1-x2)_α2In_1-α2P_t2As_1-t2(0 ≦ x2 <1, 0.5 <α2 ≦ 1, 0 ≦ t2 ≦ 1) can be used. The light guide layers 77 and 79 may contain As.
[0119]
Of course, the semiconductor laser described above is also effective when applied to a light emitting diode (LED). In this case, a visible LED having high luminance and good temperature characteristics can be obtained.
[0120]
【The invention's effect】
  As described above, according to the first aspect of the present invention, in a semiconductor light emitting device in which a heterojunction having an active layer for generating light and a cladding layer for confining light is formed on a semiconductor substrate, LayerContains As ( Al _x Ga _1-x ) _α In _1-α P _t As _1-t ( 0 ≦ x <1, 0 <α1 ≦ 1, 0 ≦ t <1 )The clad layer has a larger band gap than the active layer and contains Al having a lattice constant between GaP and GaAs (Al_yGa_1-y)_βIn_1-βP_vAs_1-v(0 <y ≦ 1, 0.5 <β <1, 0 <v ≦ 1)The active layer contains As ( Al _x Ga _1-x ) _α In _1-α P _t As _1-t ( 0 ≦ x <1, 0 <α1 ≦ 1, 0 ≦ t <1 ) Since the addition of As reduces the band gap, even when a clad layer having a large band gap close to GaP is used, it is possible to cope with elements having wavelengths longer than 600 nm such as 635 nm and 650 nm bands. . That is, the clad layer has a larger band gap than the conventional 635 nm and 650 nm band devices on the GaAs substrate, carrier overflow is reduced, and good device characteristics such as high temperature stable operation can be obtained. Accordingly, it is possible to provide a high-efficiency, high-efficiency, 635-nm, 650-nm-band red semiconductor laser, a visible light-emitting diode with high luminous efficiency, and the like.
[0127]
  Also,Claim 2According to the described invention, the claims1In the semiconductor light emitting device described above, the semiconductor substrate is made of GaPAs, and the heterojunction portion is crystal-grown on the semiconductor substrate. GaPAs having a lattice constant between GaP and GaAs is grown thick on GaP or a substrate (for example, 30 μm thick), and a material that can be substantially regarded as a GaPAs substrate is grown by a VPE (vapor phase epitaxy) method or the like. Is possible. By making the uppermost portion the same as the lattice constant of the heterojunction portion (at least the cladding layer), the present material system can be grown without lattice irregularities. Accordingly, it is possible to provide a 635 nm or 650 nm band red semiconductor laser that operates stably at a high temperature, a high output, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, a visible light emitting diode with high luminous efficiency, and the like.
[0128]
  Also,Claim 3According to the described invention, the claims1In the semiconductor light emitting device described above, the semiconductor substrate is made of GaAs or GaP, and a heterojunction portion is crystal-grown between the semiconductor substrate and the cladding layer via a relaxation buffer layer that relaxes lattice mismatch between the two. Alternatively, by forming the heterojunction portion on the GaP substrate via the relaxation buffer layer that relaxes the lattice mismatch, the lattice mismatch is relaxed and the heterojunction portion can be grown. In addition, it is possible to continuously perform the growth continuously with the same crystal growth apparatus, and it is easy and cost-effective because only one apparatus is required. Accordingly, it is possible to provide a 635 nm or 650 nm band red semiconductor laser that operates stably at a high temperature, a high output, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, a visible light emitting diode with high luminous efficiency, and the like.
[0129]
  Also,Claim 4According to the described invention,Claim 3In the semiconductor light emitting device described above, the relaxation buffer layer is composed of a graded layer whose lattice constant gradually changes from the lattice constant of the semiconductor substrate toward the growth direction and approaches the lattice constant of the cladding layer, and relaxes the graded layer. Since lattice relaxation gradually occurs when used as a buffer layer, threading dislocations can be prevented from growing above the graded layer, and the crystallinity of the heterojunction can be prevented from being lowered. Accordingly, it is possible to provide a 635 nm or 650 nm band red semiconductor laser that operates stably at a high temperature, a high output, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, a visible light emitting diode with high luminous efficiency, and the like.
[0130]
  Also,Claim 5According to the described invention,Claim 3In the described semiconductor light emitting device, the relaxation buffer layer has a strained superlattice structure in which at least two types of materials having different lattice constants are alternately stacked. By using the strained superlattice structure as the relaxation buffer layer, lattice relaxation is achieved. As a result, crystal defects associated with can be confined in the strained superlattice structure, and the crystallinity of the heterojunction can be prevented from being lowered. Accordingly, it is possible to provide a 635 nm or 650 nm band red semiconductor laser that operates stably at a high temperature, a high output, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, a visible light emitting diode with high luminous efficiency, and the like.
[0131]
  Also,Claim 6According to the described invention,Claim 3In the described semiconductor light emitting device, the relaxation buffer layer is composed of a low-temperature buffer layer grown at a temperature lower than the growth temperature of the cladding layer. By using the low-temperature buffer layer as the relaxation buffer layer, crystal defects associated with lattice relaxation are eliminated. It can be confined in the low-temperature buffer layer, and the crystallinity of the heterojunction can be prevented from being lowered. Accordingly, it is possible to provide a 635 nm or 650 nm band red semiconductor laser that operates stably at a high temperature, a high output, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, a visible light emitting diode with high luminous efficiency, and the like.
[0132]
  Also,Claim 7According to the described invention,Claim 3ThruClaim 6In the semiconductor light emitting device according to any one of the above, the relaxation buffer layer is made of GaInP or GaPAs. GaPAs or GaInP is a ternary material and is easy to control. In the case of using GaPAs, it is only necessary to add As to GaP when the semiconductor substrate is a GaP substrate, and it is only necessary to add P to GaAs when the semiconductor substrate is a GaAs substrate. In addition, in the case of GaInP, P is the only group V having a high vapor pressure, so that the interface can be easily controlled particularly when growing a strained superlattice structure. Accordingly, it is possible to provide a 635 nm or 650 nm band red semiconductor laser that operates stably at a high temperature, a high output, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, a visible light emitting diode with high luminous efficiency, and the like.
[0133]
  Also,Claim 8According to the described invention,Claim 2OrClaim 3In the semiconductor light-emitting element described above, the plane orientation of the semiconductor substrate is a plane inclined in the range of 0 ° to 54.7 ° in the [011] direction from the (100) plane, or [0-11] from the (100) plane. It is a plane inclined in the range of 10 ° to 54.7 ° in the direction or a plane equivalent to these, and the plane orientation of the semiconductor substrate is 0 ° to 54.7 in the [011] direction from the (100) plane. When the natural superlattice is formed because the inclination is in the range of 10 ° or in the range of 10 ° to 54.7 ° in the [0-11] direction from the (100) plane. Compared to, a wide gap is obtained with the same composition ratio, which is advantageous for shortening the wavelength. Further, an end face type laser usually uses a cleavage plane as a resonator. When the plane orientation of the substrate is tilted in the above direction, the cleavage plane perpendicular to the tilted direction is not perpendicular to the substrate, but when the substrate is cleaved in the tilted direction, a vertical plane is obtained, which can be used as a laser resonator. If it is tilted in a direction other than the above, the cleavage plane will not be vertical, which is not preferable. Further, by tilting the plane orientation of the substrate from the (100) plane, the hillock density can be reduced, and thereby deterioration of device characteristics and yield can be suppressed. Accordingly, it is possible to provide a 635 nm or 650 nm band red semiconductor laser that operates stably at a high temperature, a high output, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, a visible light emitting diode with high luminous efficiency, and the like.
[0134]
  Also,Claim 9According to the described invention,Claim 2OrClaim 3In the semiconductor light-emitting device described above, the surface of the GaPAs substrate is planarized by mechanical polishing before the heterojunction is crystal-grown, or after the growth of the relaxation buffer layer and before the heterojunction is crystal-grown. The surface is flattened by mechanical polishing. On the surface of the GaPAs substrate or the surface after the growth of the relaxation buffer layer, there are usually formed cross-hatched irregularities related to lattice irregularities. This unevenness can be the origin of new crystal defects when a heterojunction is grown thereon. This can be prevented by flattening by polishing and growing a heterojunction thereon. Accordingly, it is possible to provide a 635 nm or 650 nm band red semiconductor laser that operates stably at a high temperature, a high output, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, a visible light emitting diode with high luminous efficiency, and the like.
[0135]
  Also,Claim 10According to the described invention,Claim 2OrClaim 3The semiconductor light-emitting element described above is characterized in that a layer whose upper surface at the interface of the layer is flatter than the lower surface (substrate side) is provided between the semiconductor substrate and the heterojunction portion. On the surface of the GaPAs substrate or the surface after the growth of the relaxation buffer layer, there are usually formed cross-hatched irregularities related to lattice irregularities. This unevenness can be the origin of new crystal defects when a heterojunction is grown thereon. When a layer that grows by embedding such irregularities is included, the upper layer becomes flat, and this can be prevented. Accordingly, it is possible to provide a 635 nm or 650 nm band red semiconductor laser that operates stably at a high temperature, a high output, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, a visible light emitting diode with high luminous efficiency, and the like.
[0136]
  Also,Claim 11According to the described invention,Claim 10In the semiconductor light-emitting element described above, a layer whose upper surface at the interface of the layer is flatter than the lower surface (substrate side) is Se 5 × 10¹⁸cm^-3It is characterized by being GaInP doped as described above. The inventor of the present application has found that GaInP doped with Se at a high concentration has a property of growing while embedding irregularities. Thereby, since the upper surface of the interface of the layer becomes flatter than the lower surface (substrate side), it is possible to prevent generation of new crystal defects originating from unevenness when the heterojunction is grown. Accordingly, it is possible to provide a 635 nm or 650 nm band red semiconductor laser that operates stably at a high temperature, a high output, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, a visible light emitting diode with high luminous efficiency, and the like.
[0137]
  Also,Claim 12According to the described invention,Claim 3In the described semiconductor light emitting device, the relaxation buffer layer has Se of 5 × 10 5.¹⁸cm^-3It is characterized by being doped GaInP as described above, and has a high concentration of Se that has the property of growing by embedding irregularities in the relaxation buffer layer itself that is the source of generating cross-hatched irregularities related to lattice irregularities. By using GaInP doped to, the total thickness of the growth layer can be reduced by combining the effect of relieving lattice irregularities and the effect of flattening the surface. Accordingly, it is possible to provide a 635 nm or 650 nm band red semiconductor laser that operates stably at a high temperature, a high output, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, a visible light emitting diode with high luminous efficiency, and the like.
[0138]
  Also,Claim 13According to the described invention, claims 1 toClaim 12In the semiconductor light emitting device according to any one of the above, the heterojunction portion is grown by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). AlGaInP (As) -based materials have a large segregation coefficient of Al from a solution to a solid phase, and liquid layer growth is difficult from the viewpoint of composition control. Further, the vapor phase growth method (VPE) by the halogen transport method is difficult because AlCl as a raw material corrodes the quartz reaction tube. On the other hand, metal organic vapor phase epitaxy (MOCVD) or molecular beam epitaxy (MBE) is a highly non-equilibrium growth method, and growth is based on the Group III material supply rule. Is extremely effective and can grow easily. Accordingly, it is possible to provide a 635 nm or 650 nm band red semiconductor laser that operates stably at a high temperature, a high output, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, a visible light emitting diode with high luminous efficiency, and the like.
[0139]
  Also,Claim 14According to the described invention,Claim 13In the described semiconductor light emitting device, since the relaxation buffer layer is grown by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE), it is continuously used in the same device as the heterojunction crystal growth device. Therefore, it can be grown, and only one device is required, which is easy and cost-effective. Accordingly, it is possible to provide a 635 nm or 650 nm band red semiconductor laser that operates stably at a high temperature, a high output, a visible semiconductor laser that oscillates at a wavelength shorter than 600 nm at room temperature, a visible light emitting diode with high luminous efficiency, and the like.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between a lattice constant and band gap energy.
FIG. 2 is a diagram showing a configuration example of a semiconductor light emitting element according to the present invention.
FIG. 3 is a diagram showing a configuration example of a semiconductor light emitting element according to the present invention.
FIG. 4 is a diagram showing a configuration example of a semiconductor light emitting element according to the present invention.
FIG. 5 is a diagram showing a basic configuration of semiconductor light emitting devices of Examples 1 to 7 of the present invention.
6 is a diagram showing a superlattice buffer layer of Example 4. FIG.
7 is a view showing an active layer of Example 6 and Example 7. FIG.
FIG. 8 is a view showing a configuration of a semiconductor light emitting element of Example 8 of the present invention.
FIG. 9 is a diagram showing a configuration of a semiconductor light emitting element of Example 9 of the present invention.
FIG. 10 is a diagram showing a configuration of a semiconductor light emitting element of Example 10 of the present invention.
FIG. 11 shows GaP 2 ° off from the (100) plane in the [110] direction._0.4As_0.6It is a figure which shows the surface Nomarski (surface morphology) photograph of AlInP and AlInPAs on an epitaxial substrate.
[Explanation of symbols]
1 Semiconductor substrate
2 Active layer
3 Clad layer
4 Heterojunction
5 Light guide layer
6 Relaxation buffer layer
11 Semiconductor substrate
12 Graded buffer layer, superlattice buffer layer, low temperature buffer layer
13 Uniform composition layer
14,18 Cladding layer
15, 17 Light guide layer
16 Active layer
19 Cap layer
20 Contact layer
21 SiO₂
22 p-side electrode
23 n-side electrode
11 Semiconductor substrate
12 Graded buffer layer, superlattice buffer layer, low temperature buffer layer
13 Uniform composition layer
14,18 Cladding layer
15, 17 Light guide layer
16 Active layer
19 Cap layer
20 Contact layer
21 SiO₂
22 p-side electrode
23 n-side electrode
11 Semiconductor substrate
12 Graded buffer layer, superlattice buffer layer, low temperature buffer layer
13 Uniform composition layer
14,18 Cladding layer
15, 17 Light guide layer
16 Active layer
19 Cap layer
20 Contact layer
21 SiO₂
22 p-side electrode
23 n-side electrode

Claims (14)

In a semiconductor light emitting device in which a heterojunction having an active layer for generating light and a cladding layer for confining light is formed on a semiconductor substrate,
The active layer is made of (Al _x Ga _1-x ) _α In _1-α P _t As _1-t (0 ≦ x <1, 0 <α1 ≦ 1, 0 ≦ t <1) containing As,
The cladding layer has a larger band gap than the active layer and contains Al having a lattice constant between GaP and GaAs (Al _y Ga _1-y ) _β In _1-β P _v As _1-v (0 <y ≦ 1 , 0.5 <β <1, 0 <v ≦ 1). In the semiconductor light emitting device according to claim 1 Symbol placement, the semiconductor substrate is made of GaPAs, the semiconductor light-emitting device heterojunction on the semiconductor substrate is characterized in that it is grown. In the semiconductor light emitting device according to claim 1 Symbol placement, the semiconductor substrate is made of GaAs or GaP, between the semiconductor substrate and the cladding layer, heterojunction is crystal grown through the relaxed buffer layer to mitigate both the lattice mismatch A semiconductor light emitting element characterized by comprising: 4. The semiconductor light emitting device according to claim 3 , wherein the relaxation buffer layer comprises a graded layer whose lattice constant gradually changes from the lattice constant of the semiconductor substrate in the growth direction and approaches the lattice constant of the cladding layer. Semiconductor light emitting device. 4. The semiconductor light emitting device according to claim 3 , wherein the relaxation buffer layer has a strained superlattice structure in which at least two kinds of materials having different lattice constants are alternately stacked. 4. The semiconductor light emitting device according to claim 3 , wherein the relaxation buffer layer comprises a low temperature buffer layer grown at a temperature lower than the growth temperature of the cladding layer. 7. The semiconductor light emitting device according to claim 3, wherein the relaxation buffer layer is made of GaInP or GaPAs. 8. 4. The semiconductor light emitting device according to claim 2 , wherein the plane orientation of the semiconductor substrate is a plane inclined in the range of 0 ° to 54.7 ° in the [011] direction from the (100) plane, or (100) A semiconductor light emitting device characterized in that it is a surface inclined in the range of 10 ° to 54.7 ° in the [0-11] direction from the surface, or a surface equivalent thereto. 4. The semiconductor light emitting device according to claim 2 , wherein the surface of the GaPAs substrate is planarized by mechanical polishing prior to crystal growth of the heterojunction portion, or after growth of the relaxed buffer layer and the heterojunction. A semiconductor light emitting device, wherein the surface of the portion before crystal growth is flattened by mechanical polishing. 4. The semiconductor light emitting device according to claim 2 , further comprising a layer between the semiconductor substrate and the heterojunction portion, wherein the upper surface of the interface of the layer is flatter than the lower surface (substrate side). Light emitting element. 11. The semiconductor light emitting device according to claim 10 , wherein the layer whose upper surface at the interface of the layer is flatter than the lower surface (substrate side) is GaInP doped with Se at 5 × 10 ¹⁸ cm ⁻³ or more. Light emitting element. 4. The semiconductor light emitting device according to claim 3 , wherein the relaxation buffer layer is GaInP doped with Se at 5 × 10 ¹⁸ cm ⁻³ or more. 13. The semiconductor light emitting device according to claim 1, wherein the heterojunction portion is grown by metal organic vapor phase epitaxy or molecular beam epitaxy. . 14. The semiconductor light emitting device according to claim 13 , wherein the relaxation buffer layer is grown by metal organic vapor phase epitaxy or molecular beam epitaxy.

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