JP2005064101A - Epitaxial wafer and semiconductor laser using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epitaxial wafer capable of reducing the mixed crystal ratio of a material which is easily oxidized by increasing the refractive index of the entire layer other than the active region, and a semiconductor laser using the epitaxial wafer.
SOLUTION: A first conductive type second cladding region 12, a first conductive type low refractive index lowering prevention layer 21, a first conductive type first cladding region 13, an active region 14, and a first conductive type second cladding region 12 are formed on a substrate 11. A two-conductivity-type first cladding region 15, a second-conductivity-type low-refractive-index prevention layer 22, a first-conductivity-type current blocking layer 16 having a stripe-shaped opening 19, and the inside of the opening 19 and at least the opening In an epitaxial wafer having a second conductivity type second cladding region 17 in contact with the first conductivity type current block layer 16 on both sides of the part and a second conductivity type contact layer 18 in this order, the first conductivity type current block layer The refractive index of 16 is lower than the refractive index of the second conductivity type second cladding region 17, the refractive indexes of the lower refractive index prevention layers 21 and 22 are higher than the refractive index of the entire cladding region, and the lower refractive index reduction prevention layer 21. , 22 is the thickness It is made thinner than the thickness of the first conductivity type first cladding region 13 and the second conductivity type first cladding region 15.
[Selection] Figure 1

Description

  The present invention relates to an epitaxial wafer and a semiconductor laser using the same, and particularly in an actual refractive index type structure having a first conductive type current blocking layer having a lower refractive index than the second conductive type second cladding region. The present invention relates to an epitaxial wafer for increasing the refractive index of the entire layer and a semiconductor laser using the same.

  In recent years, it has been desired that the beam radiation angle of a semiconductor laser be adjusted to a specific angle when coupled to an external lens or an optical fiber of an external optical system from the viewpoint of improving the utilization efficiency of the beam radiation light.

  As a method of reducing the vertical beam radiation angle with respect to the stacking direction of the epitaxial wafer of the semiconductor laser, there is known a method of lowering the refractive index of the cladding region in contact with the active region (for example, Patent Document 1: Japanese Patent Laid-Open No. Hei 6). -104525). However, in this method, the entire layer excluding the active region has a low refractive index. For example, a semiconductor laser made of a III-V group compound semiconductor material is Al, and a semiconductor laser made of a II-VI group compound semiconductor material is Mg. This causes an increase in the mixed crystal ratio of the easily oxidizable material, and as a result, there is a problem of deteriorating the life characteristics of the semiconductor laser.

  In addition, the real refractive index type structure having the first conductive type current blocking layer having a lower refractive index than the second conductive type second cladding region absorbs light in the active region immediately below the second conductive type second cladding region. It is known that the light can be effectively controlled with a reduced amount (for example, see Patent Document 2: Japanese Patent No. 28442465). However, in this structure, since the refractive index of the current blocking layer is lower than that of the second conductivity type second cladding region, for example, in a semiconductor laser made of a III-V group compound semiconductor material, Al, II- A semiconductor laser made of a group VI compound semiconductor material has a problem in that the mixed crystal ratio of an easily oxidizable material such as Mg is increased in the current blocking layer.

  Also known are semiconductor lasers having a light field correction layer for correcting the bias of the light field due to a light seepage layer or an etching stop layer introduced to improve COD (Catastrophic Optical Damage) between the cladding regions. (For example, Patent Document 3: JP-A-8-46301, Patent Document 4: JP-A-11-26868). However, the introduction of the light exudation layer and the light field correction layer alone cannot prevent the lowering of the refractive index of the entire layer, and further improvement is required.

JP-A-6-104525 (Claims, FIG. 1) Japanese Patent No. 28442465 (Claims, FIG. 1) Japanese Patent Laid-Open No. 8-46301 (Claims, FIG. 1) Japanese Patent Laid-Open No. 11-26868 (Claims, FIG. 1)

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an actual refractive index type having a first conductivity type current blocking layer having a lower refractive index than the second conductivity type second cladding region. An object of the present invention is to provide an epitaxial wafer that can reduce the mixed crystal ratio of a material that is easily oxidized by increasing the refractive index of the layer and the entire region other than the active region, and a semiconductor laser using the epitaxial wafer.

  In order to solve the above-mentioned problems, the present inventors have intensively studied. As a result, in the real refractive index type structure having the first conductive type current blocking layer having a lower refractive index than the second conductive type second cladding region, Between the first conductivity type second cladding region and the first conductivity type first cladding region and / or between the second conductivity type first cladding region and the second conductivity type second cladding region, the same conductivity as each cladding region. By providing a low refractive index prevention layer of the mold and adjusting the refractive index and thickness of each layer and region, the increase in the mixed crystal ratio of easily oxidizable materials is suppressed, and the entire layer other than the active region is increased in refractive index The present inventors have found that this can be done and have completed the present invention.

  That is, the epitaxial wafer of the present invention and the semiconductor laser using the epitaxial wafer have the first conductivity type second cladding region, the first conductivity type first cladding region, the active region, and the second conductivity type first on the substrate. A first conductivity type current blocking layer having a cladding region, a stripe-shaped opening, and a second conductivity type second cladding in contact with the inside of the opening and at least the first conductivity type current blocking layer on both sides of the opening; Region and a second conductivity type contact layer in this order, and a first conductivity type low-refractive-index prevention layer between the first conductivity type second cladding region and the first conductivity type first cladding region, and / Or a second conductivity type low refractive index preventing layer between the second conductivity type first cladding region and the second conductivity type second cladding region, wherein the refractive index of the first conductivity type current blocking layer is Bending of the second conductivity type second cladding region The refractive index of the low refractive index reduction prevention layer is lower than the refractive index, the first conductivity type second cladding region, the first conductivity type first cladding region, the second conductivity type first cladding region, and the second conductivity type second cladding region. And the thickness of the first conductive type low refractive index lowering prevention layer and / or the second conductive type low refractive index lowering prevention layer is higher than the refractive index of the first conductive type first cladding region and the second conductive type first. The object is achieved by making the thickness smaller than that of the cladding region.

Preferred embodiments of the present invention include the following embodiments.
(1) At least one selected from the first conductivity type first cladding region, the first conductivity type second cladding region, the second conductivity type first cladding region, and the second conductivity type second cladding region has a different refractive index. An epitaxial wafer comprising a plurality of layers.
(2) The ratio of the thickness and the refractive index of the second conductivity type first cladding region to the first conductivity type first cladding region is from 0.9 to 1.1. The described epitaxial wafer.
(3) The ratio of the thickness and the refractive index of the second conductivity type second cladding region to the first conductivity type second cladding region is 0.9 to 1.1 (1) or The epitaxial wafer according to (2).
(4) The ratio of the thickness and refractive index of the second conductive type refractive index lowering prevention layer to the first conductive type refractive index lowering prevention layer is from 0.9 to 1.1 (1) The epitaxial wafer according to any one of (1) to (3).
(5) Refractive indexes of the first conductivity type first cladding region, the first conductivity type second cladding region, the second conductivity type first cladding region, and the second conductivity type second cladding region are set to be the first refractive index. The refractive index of the first conductive type first cladding region and the first conductive type second cladding region is higher than the refractive index of the conductive current blocking layer, and the refractive index of the first conductive type low refractive index reduction preventing layer. The refractive index of the second conductive type first cladding region and the second conductive type second cladding region is lower than the refractive index of the second conductive type low refractive index reduction prevention layer (1) to The epitaxial wafer according to any one of (4).
(6) At least one of the first conductivity type first cladding region and the second conductivity type first cladding region is composed of a plurality of layers having different refractive indexes, and the refraction of the layer closest to the active region among the plurality of layers The epitaxial wafer according to any one of (1) to (5), wherein a refractive index is lower than a refractive index of another layer of the plurality of layers.
(7) At least one of the first conductivity type first cladding region and the second conductivity type first cladding region is composed of a plurality of layers having different refractive indexes, and the refractive index of the second conductivity type second cladding region is The epitaxial wafer according to (6), wherein the epitaxial wafer has a refractive index lower than a refractive index of the first conductivity type second cladding region and lower than a refractive index of a layer other than the layer closest to the active region among the plurality of layers.
(8) At least one of the first conductivity type first cladding region and the second conductivity type first cladding region is composed of a plurality of layers having different refractive indexes, and the first conductivity type low refractive index lowering prevention layer and the first conductivity type The epitaxial wafer according to (6) or (7), wherein the thickness of any one of the two-conductivity-type low-refractive index prevention layers is thinner than the thickness of the plurality of layers closest to the active region .
(9) At least one of the first conductivity type first cladding region and the second conductivity type first cladding region is composed of a plurality of layers having different refractive indexes, and the thickness of the layer closest to the active region among the plurality of layers. The epitaxial wafer according to any one of (6) to (8), wherein is thinner than a total thickness of the other layers of the plurality of layers.
(10) At least one of the first conductivity type first cladding region and the second conductivity type first cladding region is formed of a plurality of layers having different refractive indexes, and the first conductivity type second cladding region and / or the first conductivity type. The epitaxial wafer according to any one of (6) to (9), wherein a refractive index of the second conductivity type second cladding region is higher than a refractive index of a layer closest to the active region among the plurality of layers.
(11) The epitaxial wafer according to any one of (1) to (10), wherein the second conductivity type low refractive index reduction preventing layer is used as an etching stop layer.
(12) The band gap energy in the bulk state of the first conductive type low refractive index lowering prevention layer and / or the second conductive type low refractive index lowering prevention layer is equal to or lower than the energy of light oscillated from the active region. The epitaxial wafer according to any one of (1) to (11).
(13) The first conductive type low refractive index preventing layer and / or the second conductive material can be formed by thinning the first conductive type low refractive index preventing layer and / or the second conductive type low refractive index preventing layer. The epitaxial wafer according to (12), wherein an effective band gap energy of the type low refractive index reduction preventing layer is made larger than energy of light oscillated from the active region.
(14) The epitaxial wafer according to any one of (1) to (13), wherein the active region includes at least two quantum well layers, two light guide layers, and one barrier layer.
(15) The epitaxial wafer according to any one of (1) to (14), wherein each of the layers is made of an arsenic III-V compound semiconductor material.
(16) The epitaxial wafer according to any one of (1) to (14), wherein each of the layers is made of a phosphorus-based III-V group compound semiconductor material.
(17) The epitaxial wafer according to any one of (1) to (14), wherein each of the layers is made of an arsenic and phosphorus III-V compound semiconductor material.
(18) The epitaxial wafer according to any one of (1) to (14), wherein each of the layers is made of a nitride III-V group compound semiconductor material.
(19) The epitaxial wafer according to any one of (1) to (14), wherein each of the layers is made of a II-VI group compound semiconductor material.
(20) A semiconductor laser using the epitaxial wafer according to any one of (1) to (19).

  In order to show the effect of introducing the low refractive index prevention layer in the epitaxial wafer of the present invention, the vertical beam radiation angle with respect to the stacking direction of the epitaxial wafer is 16 °, and the horizontal beam radiation angle is 9 °. Using four types of AlGaAs compound semiconductor epitaxial wafers having an actual refractive index type structure having a first conductive type current blocking layer having a lower refractive index than the second conductive type second cladding region obtained by calculation so that This will be described below.

  The beam emission angle of the present invention was determined by an effective refractive index approximation method generally used in the analysis of optical waveguides in lasers (“semiconductor laser (basic and applied)”, Ryoichi Ito, Michiko Nakamura. Co-edition Baifukan (1989) p98-100)). At this time, the light separation in the epitaxial growth direction and the direction perpendicular to the epitaxial growth direction was assumed to be independent from each other, and was performed by variable separation. In the case of AlGaAs used as an example in this specification, the refractive index n used in the above analysis is such that when the Al composition is x (Ga composition is “1-x”), the laser oscillation wavelength is 800 nm. It was determined according to the following formula, assuming that it was in the vicinity.

The cross-sectional structures of the above four types of epitaxial wafers and the Al mixed crystal ratio and refractive index of Al _X Ga _1-X As which are the calculation results are shown in FIGS. 4 is a cross-sectional structure in the case where the low refractive index reduction preventing layers 21 and 22 are provided, FIG. 5 is a cross-sectional structure in the case where the low refractive index reduction preventing layers 21 and 22 are not provided, and FIG. FIG. 7 shows a cross-sectional structure in which a plurality of first cladding regions 13 and 15 are formed and a plurality of low refractive index prevention layers 21 and 22 are provided. Each of the cross-sectional structures when not doing so is shown. In the four types of structures described above, in order to clarify the difference in refractive index between the case where the conductive type low refractive index reduction preventing layers 21 and 22 are provided and the case where the conductive type low refractive index prevention layers 21 and 22 are not provided, The refractive indexes of 15 and 17 and the first conductivity type current blocking layer 16 were compared.

  In the above four types of structures, the active region 14 has a SCH (Separate Confinement Heterostructure) structure having two quantum wells, and includes two quantum well layers, two light guide layers, and one barrier layer. The Al composition and thickness were the same. Also, in the layers other than the active region 14, since the thickness of the layer affects the radiation angle of the beam, for the purpose of more accurately evaluating the influence on the refractive index due to the introduction of the low refractive index prevention layers 21 and 22. The thickness of the first conductivity type second cladding region 12, the thickness of the first conductivity type low refractive index prevention layer 21 (only the structure shown in FIGS. 4 and 6), the active region 14 to the first conductivity type second cladding region 12, the distance from the active region 14 to the first conductivity type current blocking layer 16, the thickness of the second conductivity type low refractive index reduction preventing layer 22 (only the structure shown in FIGS. 4 and 6), the first conductivity type The thickness of the current blocking layer 16, the thickness of the second conductivity type second cladding region 17, and the thickness of the second conductivity type contact layer 18 are also the same for the above four types of structures.

The layer structure of the first epitaxial wafer is a structure having conductive type low refractive index prevention layers 21 and 22, and the cross-sectional structure is shown in FIG. 4. On the first conductivity type GaAs substrate _{11, Al X Ga 1-X} As the first conductivity type having a thickness of 2.50μm in (x = 0.461) second cladding region _{12, Al X Ga 1-X} As (x = 0.175) A first conductive type low refractive index prevention layer 21 having a thickness of 0.01 μm, a first conductive type first cladding region 13 having an thickness of 0.10 μm of Al _X Ga _1-X As (x = 0.461), an active region 14, The second conductivity type first cladding region 15 having a thickness of 0.10 μm with Al _X Ga _1-X As As (x = 0.461), and the second conductivity having a thickness of 0.01 μm with Al _X Ga _1-X As (x = 0.175). Type low refractive index prevention layer 22, first conductivity type current blocking layer 16 having a thickness of 1.00 μm made of Al _X Ga _1-X As (x = 0.496) in which a current flowing region is limited to a stripe shape having a width of 2.25 μm. A thickness of Al _X Ga _1-X As (x = 0.461) in contact with the current blocking layer 16 and in contact with the second conductivity type low refractive index prevention layer 22 provided under the current blocking layer 16. 50 μm second conductivity type second cladding region 1 7. A structure in which a second conductive type contact layer 18 of GaAs with a thickness of 0.50 μm is sequentially laminated.

The layer structure of the second epitaxial wafer is a structure that does not have the conductive type low refractive index prevention layers 21 and 22 with respect to the first structure shown in FIG. 4, and FIG. 5 shows a cross-sectional structure. On the first conductivity type GaAs substrate _{11, Al X Ga 1-X} As the first conductivity type having a thickness of 2.5μm by (x = 0.528) second cladding region _{12, Al X Ga 1-X} As (x = 0.528) The first conductivity type first cladding region 13 having a thickness of 0.11 μm, the active region 14, the second conductivity type first cladding region 15 having a thickness of 0.11 μm of Al _X Ga _1-X As (x = 0.528), A first conductive type current blocking layer 16 having a thickness of 1.00 μm in Al _X Ga _1-X As (x = 0.567), in which a flowing region is limited to a stripe shape having a width of 2.25 μm, and is in contact with the current blocking layer 16 A second conductivity type second cladding region 17 having a thickness of 2.50 μm and Al _X Ga _1-X As (x = 0.528) in contact with the second conductivity type first cladding region 15 provided under the block layer 16, GaAs The second conductivity type contact layer 18 having a thickness of 0.50 μm is sequentially laminated.

The layer structure of the third epitaxial wafer is a structure in the case where the conductive type low refractive index lowering prevention layers 21 and 22 are provided, and the first cladding regions 13 and 15 are compared with the first structure shown in FIG. Is a structure in which the difference in Al mixed crystal ratio is two layers of 0.010, and its cross-sectional structure is shown in FIG. On the first conductivity type GaAs substrate _{11, Al X Ga 1-X} As the first conductivity type having a thickness of 2.50μm in (x = 0.470) second cladding region _{12, Al X Ga 1-X} As (x = 0.175) The first conductive type low refractive index reduction preventing layer 21 having a thickness of 0.01 μm, Al _X Ga _1-X As (x = 0.470) and a thickness of 0.06 μm and Al _X Ga _1-X As (x = 0.480). The first conductivity type first cladding region 13 composed of two layers of 0.04 μm, the active region 14, Al _X Ga _1-X As (x = 0.480) and a thickness of 0.04 μm and Al _X Ga _1-X As (x = 0.470) and the second conductivity type first cladding region 15 consisting of two layers having a thickness of 0.06 μm, and the second conductivity type having a thickness of 0.01 μm and preventing the lowering of the refractive index of Al _X Ga _1-X As (x = 0.175). A first conductivity type current blocking layer 16 having a thickness of 1.10 μm with Al _X Ga _1-X As (x = 0.505) in which a current flowing region is limited to a stripe shape having a width of 2.25 μm, the current blocking layer 16 In contact with the first current blocking layer 16 The second conductivity type second cladding region 17 having a thickness of 2.50 μm made of Al _X Ga _1-X As (x = 0.470) in contact with the two-conduction type refractive index lowering prevention layer 22, and the second conductive type second cladding region 17 made of GaAs having a thickness of 0.50 μm. In this structure, the conductive contact layers 18 are sequentially stacked.

The layer structure of the fourth epitaxial wafer is a structure in which the conductive type low refractive index prevention layers 21 and 22 are not provided in the third structure shown in FIG. 6, and is the same as the third structure. FIG. 7 shows a cross-sectional structure in which the first cladding regions 13 and 15 are two layers having a difference in Al mixed crystal ratio of 0.01. On the first conductivity type GaAs substrate _{11, Al X Ga 1-X} As the first conductivity type having a thickness of 2.50μm in (x = 0.539) second cladding region _{12, Al X Ga 1-X} As (x = 0.539) in thickness 0.07μm and Al _X Ga _1-X as the first conductivity type composed of two layers of thickness 0.04μm at (x = 0.549) first cladding region 13, active region _{14, Al X Ga 1-X} as ( x = 0.549) and a second conductivity type first cladding region 15 having a thickness of 0.04 μm and Al _X Ga _1-X As (x = 0.539) and a thickness of 0.07 μm, a current flowing region is 2.25 μm. A first conductivity type current blocking layer 16 having a thickness of 1.10 μm with Al _X Ga _1-X As (x = 0.578) limited to a stripe shape of width, in contact with the current blocking layer 16 and under the current blocking layer 16 A second conductive type second cladding region 17 having a thickness of 2.500 μm in Al _X Ga _1-X As (x = 0.539) in contact with the provided second conductive type first cladding region 15 and a thickness of 0.50 μm in GaAs. Second conductivity type Contact layer 18 is stacked sequentially.

  Refraction obtained by calculating the above four types of structures by adjusting the Al composition and changing the refractive index so that the vertical beam radiation angle is 16 ° and the horizontal beam radiation angle is 9 ° with respect to the stacking direction of the epitaxial wafer. FIG. 8 is a graph showing the result of comparing the refractive index of the first conductivity type current blocking layer with the refractive index of the second conductivity type second cladding region.

  In each of the above four types of structures, the structures of the active regions 14 are all the same, and the Al mixed crystal ratios of the first conductivity type second cladding region 12 and the second conductivity type second cladding region 17 are all the same. It is. Further, in the first (FIG. 4) and second (FIG. 5) structures, the Al mixed crystal ratios of the second cladding regions 12 and 17 and the first cladding regions 13 and 15 are the same. Further, in each of the third (FIG. 6) and fourth (FIG. 7) structures, the Al mixed crystal ratio of the second cladding regions 12 and 17 and the second of the two layers constituting the first cladding regions 13 and 15 are used. The Al mixed crystal ratio of the layers on the cladding regions 12 and 17 side is the same. In addition, among the two layers of the first cladding regions 13 and 15, the Al mixed crystal ratio difference between the layer on the second cladding region 12 and 17 side and the layer on the active layer 14 side is 0.010 for the layer on the active layer 14 side. It was expensive. Further, the thicknesses and Al mixed crystal ratios of the first (FIG. 4) and third (FIG. 6) low-refractive index lowering prevention layers 21 and 22 are the same. As a result, the refractive indexes of the clad regions 12, 13, 15, and 17 need only be compared with the structures of the first conductivity type second clad region 12, and FIG. The refractive indexes of the first conductivity type second cladding region 12 and the current blocking layer 16 are shown.

  From FIG. 8, the first structure (FIG. 4) and the third structure (FIG. 6), which are epitaxial wafers having the low refractive index prevention layers 21 and 22, are more conductive type low refractive index prevention layers. Compared to the second structure (FIG. 5) and the fourth structure (FIG. 7) that do not have 21, 22, both the first conductivity type second cladding region 12 and the first conductivity type current blocking layer 16 are both. It is clear that the refractive index is high and the entire layer structure other than the active region 14 can be made high in refractive index.

  The epitaxial wafer of the present invention includes a first conductivity type low refractive index preventing layer and / or a second conductivity type first cladding region between the first conductivity type second cladding region and the first conductivity type first cladding region. A second conductivity type low refractive index preventing layer is provided between the second conductivity type second cladding regions, the refractive index of the first conductivity type current blocking layer is lower than that of the second conductivity type second cladding region, and the low refractive index. The refractive index of the anti-reflection layer is higher than the refractive index of the entire cladding region, and the thickness of the low-refractive index prevention layer is thinner than the thicknesses of the first conductivity type first cladding region and the second conductivity type first cladding region. By having this structure, the present invention can reduce the mixed crystal ratio of the easily oxidizable material even when the easily oxidizable material is used, and can increase the refractive index of the entire layer other than the active region. It is possible to provide an epitaxial wafer having a beam radiation angle of 2 mm and a semiconductor laser using the same.

  Hereinafter, the epitaxial wafer of the present invention and the semiconductor laser using the same will be described in detail. In the present specification, “to” is used as a meaning including numerical values described before and after the lower limit value and the upper limit value.

  1 to 3 show preferred embodiments of the epitaxial wafer and the semiconductor laser of the present invention. The epitaxial wafer and semiconductor laser of the present invention will be described below with reference to these drawings.

  The epitaxial wafer shown in FIG. 1 includes a first conductive type second cladding region 12, a first conductive type low refractive index prevention layer 21, a first conductive type first cladding region 13, an active region 14 on a substrate 11. The second conductivity type first cladding region 15, the second conductivity type low refractive index prevention layer 22, the first conductivity type current blocking layer 16 having the stripe-shaped opening 19, the opening 19, and at least both sides of the opening 19 A second conductivity type second cladding region 17 and a second conductivity type contact layer 18 in contact with the first conductivity type current blocking layer 16 are formed in this order.

  Note that the expression “region” in this specification includes both a single layer and a plurality of layers having different refractive indexes. The expression “formed in the order of layer A (region) and layer B (region)” means that the layer B (region) is formed so that the bottom surface of layer B (region) is in contact with the upper surface of layer A (region). And the case where one or more layers (regions) are formed on the upper surface of the A layer (region) and the B layer (region) is further formed on the layer (region). Further, the upper surface of the A layer (region) and the bottom surface of the B layer (region) are in partial contact, and in other portions, one or more layers (regions) are provided between the A layer (region) and the B layer (region). Is also included in the above expression.

In FIG. 1, the substrate 11 is not particularly limited in terms of conductivity and material as long as a double heterostructure crystal can be grown thereon. For example, AlGaAs and AlGaInN materials, which are arsenic III-V compound semiconductor materials, AlGaInP materials, which are phosphorus III-V compound semiconductor materials, and arsenic and phosphorus III-V compound semiconductor materials. GaInAsP-based and AlGaInAsP-based materials, nitride-based III-V compound semiconductor materials such as AlGaInN-based materials, AlGaInNAs-based materials, AlGaInNP-based materials, and II-VI-group compound semiconductor materials such as MgZnCdSSe-based materials can be applied. . Preferably, it is a conductive substrate. Specifically, a crystal substrate such as GaAs, GaP, InP, ZnSe, ZnO, Si, AlN, and sapphire suitable for crystal thin film growth on the substrate, or a crystal substrate having a zinc blende structure can be used. Further, the substrate 11 may be a hexagonal substrate, and for example, a substrate made of Al ₂ O ₃ , 6H—SiC, or the like may be used.

  On the substrate 11, a buffer layer having a thickness of about 0.2 to 2 μm can be formed so as to prevent normal substrate defects from being brought into epitaxial growth.

  The thickness of the substrate 11 can be appropriately determined by design. For example, in the epitaxial wafer, the thickness of the substrate 11 is suitably in the range of 100 to 700 μm, preferably in the range of 200 to 650 μm, and more preferably in the range of 250 to 500 μm. In the semiconductor laser, the thickness of the substrate 11 is suitably 50 to 300 μm, preferably 60 to 200 μm, and more preferably 70 to 150 μm.

  A compound semiconductor layer including the active region 14 is formed on the substrate 11. The compound semiconductor layer includes a cladding region having a refractive index lower than that of the lowest refractive index layer in the active region 14 on the upper and lower sides of the active region 14, and the region on the substrate side is a first conductivity type cladding region, The other epitaxial region functions as a second conductivity type cladding region.

  The epitaxial wafer of the present invention includes a first conductivity type second cladding region 12 and a first conductivity type first cladding region 13 on the substrate side, a second conductivity type first cladding region 15 on the other epitaxial side, and a second conductivity type second cladding region. Two cladding regions 17 are formed respectively. Each clad region may be a single layer or may be composed of a plurality of layers. When the cladding region is composed of a plurality of layers, the cladding region is preferably composed of a plurality of layers having different refractive indexes.

  In the present invention, by forming a clad region into a plurality of layers and further introducing low refractive index reduction preventing layers 21 and 22 described later, the beam radiation angle of the semiconductor laser or the refractive index of each layer of the epitaxial wafer can be controlled. This makes it possible to freely design the beam radiation angle oscillated from the semiconductor laser, and at the same time, relatively free optical design even when the material composition is restricted due to the use of selective etching. Can be done.

  The materials used to form the first conductivity type second cladding region 12, the first conductivity type first cladding region 13, the second conductivity type first cladding region 15 and the second conductivity type second cladding region 17 are actually used. The material is not particularly limited as long as it is a material capable of producing a refractive index type structure, and can be appropriately determined depending on the design. For example, AlGaAs and AlGaInAs materials that are arsenic III-V compound semiconductor materials, AlGaInP materials that are phosphorus III-V compound semiconductor materials, and arsenic and phosphorus III-V compound semiconductor materials GaInAsP-based and AlGaInAsP-based materials, nitride-based III-V compound semiconductor materials such as AlGaInN-based materials, AlGaInNAs-based and AlGaInNP-based materials, and II-VI group compound semiconductor-based materials such as MgZnCdSSe-based materials may be applied. It is preferable to use the same semiconductor material as that of the active region 14, and it is particularly preferable to use an AlGaAs-based, AlGaIn-based, GaInAsP-based, or AlGaInN-based semiconductor material that has been attracting attention in practical use.

  The thickness of each cladding region can be determined as appropriate depending on the design, but in order to efficiently obtain the effect of lowering the refractive index of the lower refractive index prevention layers 21 and 22, the first conductivity type first cladding. In the case of the region 13 and the second conductivity type first cladding region 15, it is suitably in the range of 0.05 to 0.5 μm, preferably in the range of 0.1 to 0.4 μm, 0.15 More preferably, it is in the range of ˜0.3 μm. Further, in the case of the first conductivity type second cladding region 12 and the second conductivity type second cladding region 17, it is appropriate to be in the range of 0.5 to 5 μm, and in the range of 0.7 to 4 μm. The range of 1 to 3 μm is more preferable.

In the case of the first conductivity type second cladding region 12, the carrier concentration of each cladding region is preferably 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , and 5.0 × 10 ^{17 to} 5 More preferably, it is 0.0 × 10 ¹⁸ cm ⁻³ . In the case of the first conductivity type first cladding region 13, it is preferably 5 × 10 ^{16 to} 5 × 10 ¹⁸ cm ⁻³ , and is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁸ cm ⁻³ . More preferably. In the case of the second conductivity type first cladding region 15, it is preferably 5 × 10 ^{16 to} 5 × 10 ¹⁸ cm ⁻³ , and 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁸ cm ⁻³ cm ^{−. 3} is more preferable. In the case of the second conductivity type second cladding region 17, it is preferably 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , and 5.0 × 10 ^{17 to} 5.0 × 10 ¹⁸ cm ^−3. More preferably.

  The structure of the active region 14 is not particularly limited, and the refractive index is higher than that of the first conductivity type first cladding region 13 and the second conductivity type first cladding region 15 that are generally used for AlGaAs self-pulsation type compound semiconductor lasers. It may be a high bulk active layer. Further, it may be a structure composed of an active layer and a light guide layer that are often used for lowering the threshold of a high-power semiconductor laser or semiconductor laser. The active layer is preferably a quantum well structure composed of a single quantum well or multiple quantum wells that are partitioned between the quantum wells by a barrier layer. This quantum well structure has a light guide layer in at least one, and the refractive index of the light guide layer is higher than the refractive indexes of the first conductivity type first cladding region 13 and the second conductivity type first cladding region 15; A SCH (Separate Confinement Heterostructure) structure lower than the refractive index of the quantum well layer or a GRIN-SCH (Graded Index-Separate Confinement Heterostructure) structure having a portion in which the refractive index of the light guide layer is continuously changed may be used. .

  When the active region 14 has a quantum well structure, at least one of a quantum well layer, a barrier layer, and an optical guide layer such as a GaInP quantum well layer, an AlGaInP barrier layer, and an AlGaInP light guide layer often used in an AlGaInP compound semiconductor laser. One may have a strained layer. Further, part or all of the light guide layer and the barrier layer may be the first conductivity type or the second conductivity type.

  The thickness of the active region 14 can be appropriately determined by design. For example, in the case of a bulk active layer, the thickness is suitably 0.02 to 0.2 μm, more preferably 0.03 to 0.1 μm, and 0.04 to 0.08 μm. Is more preferable. When the active layer has a single quantum well (SQW) structure, the thickness is usually 10 nm or less, and when the active layer has a multiple quantum well (MQW) structure, the thickness is 0.02 to 0.3 μm. It is suitable, it is preferable that it is 0.03-0.2 micrometer, and it is more preferable that it is 0.05-0.15 micrometer.

  The material used in the active region 14 is appropriately determined depending on the design. For example, AlGaAs and AlGaInAs materials, which are arsenic III-V compound semiconductor materials, and AlGaInP materials, which are phosphorus III-V compound semiconductor materials, are used. Materials, ArIn and Phosphorus III-V compound semiconductor materials GaInAsP and AlGaInAsP materials, Nitride III-V compound semiconductor materials AlGaInN, AlGaInNAs and AlGaInNP materials, II-VI group Examples thereof include MgZnCdSSe-based materials that are compound semiconductor materials, and it is preferable to apply AlGaAs-based, AlGaInP-based, GaInAsP-based, and AlGaInN-based materials that are attracting particular attention in terms of practical use.

  On the active region 14, a second conductivity type first cladding region 15, a second conductivity type low refractive index prevention layer 22, a first conductivity type current blocking layer 16, and a second conductivity type second cladding region 17 are arranged in this order. It is formed. The first conductivity type current blocking layer 16 is a layer for confining the current in the opening 19 and concentrating the light in the horizontal direction with respect to the stacking direction of the epitaxial wafer in the current confined region in order to cause laser oscillation. The material is not particularly limited as long as it is a semiconductor of the first conductivity type. The first conductivity type current blocking layer 16 includes, for example, AlGaAs-based and AlGaInN-based materials that are arsenic III-V compound semiconductor materials, AlGaInP-based materials that are phosphorus-based III-V compound semiconductor materials, arsenic and phosphorus Group III-V compound semiconductor materials GaInAsP and AlGaInAsP materials, nitride III-V compound semiconductor materials AlGaInN, AlGaInNAs and AlGaInNP materials, II-VI group compound semiconductor materials Examples thereof include MgZnCdSSe-based materials, and it is particularly preferable to apply the same semiconductor material as the cladding region and active region. Also, different semiconductor materials can be used by matching lattice constants.

  The refractive index of the first conductivity type current blocking layer 16 is preferably lower than the refractive index of the second conductivity type second cladding region 17 (actual refractive index guide structure). By controlling the refractive index in this way, it becomes possible to reduce the operating current as compared with the conventional loss guide structure. The refractive index of the first conductivity type current blocking layer 16 is preferably lower than the refractive index of the second conductivity type second cladding region 17 and lower than the refractive index of the second conductivity type first cladding region 15, More preferably, it is lower than the refractive index of the regions 12, 13, 15 and 17.

  The first conductivity type current blocking layer 16 is composed of two or more layers having different refractive indexes, carrier concentrations or conductivity types in order to control the light distribution (particularly the light distribution in the lateral direction) or improve the current blocking function. It may be formed. Further, a surface protective layer (not shown) may be formed on the first conductivity type current blocking layer 16 to suppress surface oxidation or to protect the surface of the process. Although the conductivity type of the surface protective layer is not particularly defined, the current blocking function can be improved by adopting the second conductivity type.

  If the first conductivity type current blocking layer 16 is too thin, current blocking may be hindered. Therefore, the thickness is preferably in the range of 0.1 to 3 μm, and preferably 0.2 to 2.0 μm. It is more preferable that the thickness is in the range of 0.3 to 1.2 μm.

  For example, as shown in the cross-sectional structure of FIG. 1, the first conductivity type current blocking layer 16 is formed on the second conductivity type low refractive index lowering prevention layer 22, and a part thereof is opened in a stripe shape. In addition, an internal stripe structure in which the stripe-shaped openings 19 are filled with the second conductivity type second cladding region 17 can be adopted. Further, as shown in the cross-sectional structure of FIG. 2, the first conductivity type current blocking layer 16 is a second conductivity type second cladding region having a ridge stripe shape on the second conductivity type low refractive index prevention layer 22. 17 may be provided, and a buried ridge structure embedded in both side portions of the second conductivity type second cladding region 17 may be employed.

  In the case of adopting a ridge structure in which the first conductivity type current blocking layer 16 is embedded, a cap layer is formed on the second conductivity type second cladding region 17 in order to prevent oxidation of the second conductivity type second cladding region 17. 31 is preferably provided. The cap layer 31 can be formed by appropriately selecting a material that does not oxidize and has a low electric resistance, and has a thickness in the range of 0.01 to 0.5 μm and a range of 0.01 to 0.3 μm. And is more preferably in the range of 0.02 to 0.2 μm.

  Prior to forming the electrode after forming the current blocking layer 16 and the second conductivity type second cladding layer 17, in order to reduce the contact resistance with the electrode material, a contact layer 18 having a low resistance (high carrier concentration) is formed. It is preferable to form. In particular, when the epitaxial wafer of the present invention is used as a semiconductor laser, it is preferable to form the electrode after forming the contact layer 18 over the entire surface of the uppermost layer on which the electrode is to be formed.

At this time, the material of the contact layer 18 is usually selected from materials having a band gap smaller than that of the clad layer, and preferably has a low resistance and an appropriate carrier density in order to achieve ohmic properties with the metal electrode. The carrier density is preferably 1.0 × 10 ^{18 to} 1.0 × 10 ²⁰ cm ⁻³ , more preferably 1.0 × 10 ^{18 to} 5.0 × 10 ¹⁹ cm ⁻³ . Most preferably, it is 0 * 10 < ¹⁸ > -3.0 * 10 < ¹⁹ > cm < ^-3 >.

  Next, the low refractive index reduction preventing layers 21 and 22 will be described. The epitaxial wafer of the present invention includes a first conductivity type low refractive index prevention layer 21 and a second conductivity type first cladding region 15 between the first conductivity type second cladding region 12 and the first conductivity type first cladding region 13. And at least one of the second conductivity type low refractive index prevention layer 22 is provided between the second conductivity type second cladding region 17. The epitaxial wafer shown in FIG. 1 is an embodiment having both the first conductive type low refractive index lowering prevention layer 21 and the second conductive type low refractive index lowering prevention layer 22.

  In the present invention, the refractive indexes of the low-refractive index lowering prevention layers 21 and 22 are the total cladding region, that is, the first conductivity type second cladding region 12, the first conductivity type first cladding region 13, and the second conductivity type first cladding region. 15 and the refractive index of any region of the second conductivity type second cladding region 17 is higher. More specifically, the difference in refractive index between the low refractive index reduction preventing layers 21 and 22 and the entire cladding region is preferably 0.05 or more, more preferably 0.1 or more, and 0.15 The above is most preferable. If the difference in refractive index between the two layers is 0.05 or more, the entire layer can have a high refractive index.

  The thicknesses of the low refractive index preventing layers 21 and 22 are the thicknesses of the first conductivity type first cladding region 13 and the second conductivity type first cladding region 15 (in the case where the cladding region is composed of a plurality of layers, the thickness is most If it is thinner than the thickness of the near layer, there is no particular limitation, and it can be determined appropriately by design. Specifically, the thicknesses of the low refractive index reduction preventing layers 21 and 22 are preferably in the range of 0.5 nm to 0.05 μm, more preferably in the range of 1 nm to 0.03 μm, and 1 nm to 0.03 μm. Most preferably, it is in the range of 02 μm.

  Materials applicable to the low refractive index reduction preventing layers 21 and 22 are not particularly limited. For example, arsenic III-V compound semiconductor materials such as AlGaAs and AlGaInN materials, and phosphorus III-V compound semiconductor materials. AlGaInP-based materials, arsenic and phosphorous III-V compound semiconductor materials GaInAsP-based and AlGaInAsP-based materials, nitride-based III-V group compound semiconductor materials AlGaInN-based, AlGaInNAs-based materials, and AlGaInNP-based materials An MgZnCdSSe-based material, which is a II-VI group compound semiconductor material, can be applied, and it is particularly preferable to apply the same semiconductor material as that of the cladding regions 12, 13, 15, and 17.

  Since the refractive index lowering prevention layers 21 and 22 are different in refractive index from the cladding region and the current blocking layer, the mixed crystal ratio of the cladding region and the current blocking layer is also different in the mixed crystal ratio of semiconductor. For this reason, when etching such as wet or dry having composition selectivity is performed, it can serve as an etching preventing layer.

  Even when a material that absorbs the energy of light oscillated from the active region 14 is used for the low refractive index prevention layers 21 and 22, the refractive index and conductivity type of the cladding regions 12, 13, 15, and 17 are low. The difference in refractive index between the refractive index preventing layers 21 and 22 can be increased. For this reason, the conductive type refractive index lowering prevention layers 21 and 22 can function as effective layers for preventing the lowering of the refractive index.

  The low refractive index reduction preventing layers 21 and 22 are effective even when the thickness is very thin. Therefore, in the present invention, even when a material that absorbs energy of light oscillated from the active region is used in the bulk state, the low refractive index reduction preventing layers 21 and 22 are made quantum thin by reducing the thickness. Absorption of light oscillating from the active region can be prevented by using the effect. Even in this case, the low refractive index reduction preventing layers 21 and 22 can function as effective layers for preventing the low refractive index reduction.

  The band gap energy in the bulk state of the low refractive index reduction preventing layers 21 and 22 can be made equal to or lower than the energy of light oscillated from the active region 14. A generally used semiconductor material has a refractive index that decreases in response to a decrease in band gap energy. Therefore, if it is less than the energy of light oscillated from the active region 14, the refractive index of the cladding region is effectively reduced. The difference can be increased. Further, the effective band cap energy of the low refractive index reduction preventing layers 21 and 22 is made larger than the energy of the light oscillated from the active region 14, thereby suppressing the absorption of the oscillated light, and using the light effectively, and This is preferable from the viewpoint of reducing the threshold current and the operating current.

Next, the relationship between the refractive index and thickness of the low refractive index reduction preventing layer and each layer (or region) will be described.
In the epitaxial wafer of the present invention, the effect of increasing the refractive index by the lower refractive index prevention layers 21 and 22 is due to the difference in refractive index between the cladding region and the lower refractive index prevention layer and the thickness of the lower refractive index prevention layer. Involved. That is, the epitaxial wafer of the present invention has an effect of increasing the refractive index that is effective when the refractive index of the cladding region is lower than the refractive index of the same conductivity type low refractive index reduction preventing layer.

  When the cladding regions 12, 13, 15, and 17 are formed of a plurality of layers (hereinafter, also referred to as “multiple layers”), in particular, the first conductivity type first cladding region 13 and / or the second conductivity type first cladding region. 15 (hereinafter also referred to as “first cladding region”) is composed of a plurality of layers, the band gap energy is reduced by lowering the refractive index of the layer closest to the active region 14 (lowering the refractive index). And carriers can be effectively confined in the active region 14.

  Note that the first cladding regions 13 and 15 may be formed in a plurality of layers and have a low refractive index only in a cladding region that is effective for suppressing carriers that are likely to overflow. The difference in refractive index between the layer closest to the first clad regions 13 and 15 formed into a plurality of layers and the layer having the next lowest refractive index after the layer closest to the active region 14 is usually 0.03 or less. , 0.01 or less, it is possible to effectively confine carriers in the active region 14.

  Further, as described above, when the first conductivity type first cladding region 13 or the second conductivity type first cladding region 15 is made into a plurality of layers and the refractive index of the layer closest to the active region 14 is lowered, the epitaxial wafer In order to make it easier to control the vertical beam radiation angle with respect to the stacking direction, the refractive index of the second conductivity type second cladding region 17 is set to another cladding region (that is, the first conductivity type second cladding region 12, the first conductivity type). It is effective to make it lower than the refractive index of the first type cladding region 13 and the second conductivity type first cladding region 15), preferably the first conductivity type second cladding region. When the cladding layer is composed of a plurality of layers, the refractive index of the layer showing the highest refractive index among the plurality of layers constituting the second conductivity type second cladding region 17 is different from that of the other cladding region (preferably, the first cladding region). Refraction of a layer (preferably a layer other than the layer closest to the active region 14) exhibiting the highest refractive index among a plurality of layers constituting the first conductivity type first cladding region 13 or the second conductivity type first cladding region 15). It is thought that it is further effective to make it lower than the rate. These refractive index differences are preferably 0.05 or less, but can be effectively used even when they are 0.03 or less, and even 0.01 or less.

  When the clad region is formed into a plurality of layers, there is a possibility that the electric resistance is increased due to an increase in the heterointerface. As a means for preventing this increase in electrical resistance, it is effective to reduce the thickness of the low refractive index prevention layers 21 and 22. By reducing the thickness of the low-refractive index prevention layer, it is possible to reduce wasteful current flowing in a direction transverse to the stacking direction and to reduce electric resistance. In this case, the first conductive type first cladding region 13 and / or the thickness of either one of the first conductive type low refractive index lowering prevention layer 21 and the second conductive type low refractive index lowering prevention layer 22 is formed. It is effective to make it thinner than the thickness of the layer closest to the active region 14 among the layers of the second conductivity type first cladding region 15 and not more than 50% of the thickness of the layer closest to the active region 14 of the first cladding region. More preferably, the thickness is set.

  As described above, when the first cladding regions 13 and 15 are formed in a plurality of layers and the refractive index of the layer closest to the active region 14 is lowered, the refractive index is lowered in a generally used semiconductor light emitting material. By doing so, the band gap energy increases, and this is considered to be a factor of current blocking (an increase in electrical resistance). However, since it has a carrier confinement effect in the active region 14, reducing the thickness of the layer closest to the active region 14 is effective as a means for reducing an increase in electrical resistance. In this case, it is effective that the thickness of the nearest layer among the active regions 14 of the first cladding regions 13 and 15 is thinner than the total thickness of the other layers among the plurality of layers constituting the first cladding regions 13 and 15. The thickness of the closest layer among the active regions 14 of the first cladding regions 13 and 15 is 50% or less with respect to the total thickness of the plurality of layers constituting each region of the first cladding regions 13 and 15. It is preferable to make it 30% or less.

  In addition, as described above, when the first cladding region is formed in a plurality of layers and has a low refractive index, the refraction of the second conductivity type second cladding region 17 is made easy to control the vertical beam radiation angle with respect to the stacking direction of the epitaxial wafer. The refractive index is made lower than that of the other cladding regions (the first conductivity type second cladding region 12, the first conductivity type first cladding region 13, and the second conductivity type first cladding region 15). In this case, a generally used semiconductor light emitting material has a large band gap energy, which is one of the factors for blocking current (increasing electric resistance). Therefore, it is also effective to limit the refractive index. . In this case, the refractive index of the first conductivity type second clad region 12 or the second conductivity type second clad region 17 is the same as the plurality of the first conductivity type first clad region 13 or the second conductivity type first clad region 15. Of these layers, the refractive index of the layer closest to the active region may be higher.

  In the epitaxial wafer of the present invention, when the light distribution is symmetric with respect to the active region 14, the layer configuration of the portion excluding the first conductivity type current blocking layer 16 around the active region 14, that is, the first cladding region 13. 15 and the second cladding regions 12 and 17 and the low activation prevention layers 21 and 22 are arranged symmetrically in the vertical direction. In particular, since the adjustment of the thickness and refractive index of the first conductivity type first cladding region 13 and the second conductivity type first cladding region 15 close to the active region 14 effectively affects the light distribution, the first conductivity type first The ratio of the thickness and refractive index of the second conductivity type first cladding region 15 to the thickness and refractive index of the cladding region 13 is preferably 0.9 to 1.1, and preferably 0.95 to 1.05. Is more preferable, and 0.98 to 1.02 is most preferable.

  In addition, since the ratio of the thicknesses of the refractive index lowering prevention layers 21 and 22 to the refractive index also acts effectively on the light distribution, the second conductive type lowering of the first conductive type lowering refractive index prevention layer 21 is effective. It is also effective to set the thickness ratio and refractive index ratio of the refractive index preventing layer 22 to 0.9 to 1.1, preferably 0.95 to 1.05, more preferably 0.98 to 1.02. It is.

  In addition, since the ratio of the thickness and refractive index of the second cladding regions 12 and 17 also acts effectively on the light distribution, the second conductivity type second cladding region 17 with respect to the first conductivity type second cladding region 12 It is also effective to make the ratio of thickness and refractive index 0.9 to 1.1, preferably 0.95 to 1.05, more preferably 0.98 to 1.02.

  When it is desired to make the light distribution more ideally symmetrical with respect to the active region 14, the ratio of the thickness of the second conductive type first cladding region 15 to the first conductive type first cladding region 13 and the ratio of the refractive index, The ratio of the thickness and the refractive index of the second conductive type low refractive index prevention layer 22 to the first conductive type low refractive index prevention layer 21 and the second conductive type second to the first conductive type second cladding region 12. The ratio of the thickness of the cladding region 17 to the ratio of refractive index is preferably 0.9 to 1.1, more preferably 0.95 to 1.05, and 0.98 to 1.02. Most preferably.

  On the other hand, when the light distribution is made asymmetric with respect to the active region 14, it can be realized by making the layer configuration of the portion excluding the first conductivity type current blocking layer 16 around the active region 14 asymmetric. In particular, since the adjustment of the thickness and refractive index of the first cladding regions 13 and 15 close to the active region 14 effectively affects the light distribution, the second conductivity type first with respect to the first conductivity type first cladding region 13 is used. It is preferable that the thickness ratio and the refractive index ratio of the cladding region 15 be less than 0.9 or greater than 1.1.

  In addition, since the ratio of the thickness of the low refractive index prevention layers 21 and 22 and the ratio of the refractive index also work effectively on the light distribution, when making the light distribution asymmetric with respect to the active region, It is preferable that the ratio of the thickness of the second conductive type refractive index lowering prevention layer 22 and the refractive index ratio to the first conductive type refractive index lowering prevention layer 21 is less than 0.9 or larger than 1.1.

  When it is desired to make the light distribution ideally asymmetric with respect to the active region, the ratio of the thickness of the second conductivity type first cladding region 15 to the first conductivity type first cladding region 13 and the ratio of the refractive index, The ratio of the thickness and the refractive index of the second conductive type low refractive index prevention layer 22 to the first conductive type low refractive index prevention layer 21 and the second conductive type second to the first conductive type second cladding region 12. It is preferable that the ratio of the thickness and refractive index of the cladding region 17 is less than 0.9 or greater than 1.1.

The method for producing the epitaxial wafer of the present invention is not particularly limited. As the epitaxial growth method, it is preferable to use a vapor phase growth method such as a halogen transport method, a metal organic chemical vapor deposition method (MOCVD), or a molecular beam epitaxy method (MBE) because a high-quality crystal with few crystal defects can be obtained. Among these, MOCVD and MBE are methods that can precisely control the film thickness and composition of the crystal, and thus these methods are preferably used. In the MOCVD method, trimethylgallium (TMG), trimethylaluminum (TMA), trimethylindium (TMI), etc. are used as group III materials, and arsine (AsH ₃ ), phosphine (PH ₃ ), ammonia (NH) as group V materials. ₃ ) Grow crystals in the reaction vessel using etc. MBE is a method that normally uses metal vapor obtained by heating a metal raw material, but enables growth in high vacuum by introducing gaseous plasma or hydride gas such as organic metal or N _2. To do.

  As the n-type dopant, Si, Se, S or the like is used in the III-V group, and Cl or the like is used in the II-VI group. In MOCVD, it is supplied by organic metal or hydride gas, and in MBE, it is supplied by metal vapor or sulfide. On the other hand, as the p-type dopant, Zn, Mg, Cd, Be, or the like is used in the III-V group system, and is supplied by organic metal in MOCVD and by metal vapor in MBE. In addition, N is generally used in the II-VI group system, and normally, in MBE, N is supplied in a plasma state.

  Next, the semiconductor laser of the present invention will be described. The semiconductor laser of the present invention can be manufactured using the epitaxial wafer of the present invention. The configuration and the manufacturing method of the semiconductor laser of the present invention are not particularly limited, and the semiconductor laser can be manufactured using a normal method used when manufacturing a semiconductor laser from an epitaxial wafer.

  As a preferred embodiment of the semiconductor laser of the present invention, a semiconductor laser whose sectional view is shown in FIG. 3 can be mentioned. The semiconductor laser shown in FIG. 3 is manufactured by providing electrodes 23 and 23 on the epitaxial layer 20 side and the substrate 11 side of the epitaxial wafer of the present invention, respectively. When a semiconductor laser of the same type is manufactured using a conventional epitaxial wafer that does not have a conductive type refractive index reduction preventing layer, the refractive index of the epitaxial layer needs to be lowered to obtain a desired beam radiation angle, For this purpose, the mixed crystal ratio of a material that is easily oxidized must be increased, resulting in oxidation and the like, resulting in a problem of device deterioration.

  Hereinafter, the present invention will be described in more detail with reference to specific examples. The materials, reagents, ratios, operations, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

(Example 1)
The epitaxial wafer was manufactured using MOCVD. Using trimethylgallium (TMG), trimethylaluminum (TMA), and arsine (AsH ₃ ) as source gases, an n-type Al _0.52 Ga _0.48 As second cladding region 102, n-type GaAs low Refractive index prevention layer 201, n-type first clad region 103 composed of two layers of Al _X0.52 Ga _0.48 As and Al _0.55 Ga _0.45 As, active region 104, two of Al _0.55 Ga _0.45 As and Al _0.52 Ga _0.48 As A p-type first cladding region 105 made of layers, a p-type GaAs low-refractive index prevention layer 202, and an n-type Al _X0.65 Ga _0.35 As current blocking layer 106 were successively grown. Next, patterning was performed on the n-type Al _X0.65 Ga _0.35 As current blocking layer 106 using a resist to form a mask having holes with stripes having a predetermined width. Next, the n-type Al _X0.65 Ga _0.35 As current blocking layer 106 is etched using the mask as an etching mask and the p-type GaAs low refractive index prevention layer 202 as an etching stop layer of the opening 109, and then p-type Al _{A 0.52} Ga _0.48 As second cladding region 107 and a p-type GaAs contact layer 108 were grown. Next, after the n-type GaAs substrate 101 is thinned to about 100 μm, an n-side electrode is formed on the n-type GaAs substrate 101 side and a p-side electrode is formed on the p-type GaAs contact layer 108 side by vapor deposition. Cleaved in the direction perpendicular to the shape of chips. Further, a semiconductor laser was manufactured by coating the end face to control the refractive index.

FIG. 9 shows the cross-sectional structure of the epitaxial wafer before producing the electrode obtained by the above production method, and the Al mixed crystal ratio, refractive index, film thickness, and conductivity type of Al _X Ga _1-X As of each layer. The epitaxial wafer of Example 1 has an n-type GaAs substrate 101 having a thickness of 350 μm, an n-type Al _0.52 Ga _0.48 As second cladding region 102 having a thickness of 3.00 μm, and an n-type GaAs having a thickness of 0.003 μm to prevent a low refractive index. The layer 201, an n-type first cladding region 103 composed of two layers of Al _0.52 Ga _0.48 As having a thickness of 0.115 μm and Al _0.55 Ga _0.45 As having a thickness of 0.075 μm, an active region 104 having a thickness of 0.07 μm, and a thickness of 0.075 μm P-type first clad region 105 composed of two layers of Al _0.55 Ga _0.45 As and 0.15 μm thick Al _0.52 Ga _0.48 As, p-type GaAs low-refractive index prevention layer 202 having a thickness of 0.003 μm, a region through which current flows The n-type Al _0.65 Ga _0.35 As current blocking layer 106 and the n-type current blocking layer 106 with a thickness of 1.00 μm are provided under the n-type current blocking layer 106. P-type low refractive index Prevention layer having a thickness of 3.00μm which contact with 202 p-type Al _0.52 Ga _0.48 As second cladding region 107, p-type GaAs contact layer 108 having a thickness of 1.50μm are sequentially laminated.

  As a result of calculation using the effective refractive index approximation method in the layer structure of the epitaxial wafer, the vertical beam radiation angle with respect to the stacking direction was 13 °, and the horizontal beam radiation angle was 9 °. In addition, as a result of actually manufacturing a semiconductor laser with this structure and measuring the beam radiation angle, the vertical beam radiation angle is 13 ° and the horizontal beam radiation angle is 8 °, which is almost the same as that obtained by calculation. I was able to.

The epitaxial wafer of the present invention can be used for various semiconductor lasers, and is particularly suitable for an external lens or an optical fiber of an external optical system that is required to be adjusted to a specific angle with a suitable beam radiation angle. Is available.

It is sectional drawing which shows the structure of the epitaxial wafer which has an internal stripe type structure of this invention. It is sectional drawing which shows the structure of the epitaxial wafer of the buried ridge structure of this invention. It is one embodiment of the semiconductor laser using the epitaxial wafer of this invention. It is sectional drawing which shows the structure at the time of providing the low-refractive-index prevention layer in the epitaxial wafer using the AlGaAs type compound semiconductor material of this invention. It is sectional drawing which shows the structure at the time of not providing the low-refractive-index prevention layer in the epitaxial wafer using the conventional type AlGaAs type compound semiconductor material. In the epitaxial wafer using the AlGaAs type compound semiconductor material of this invention, it is sectional drawing of a structure when the 1st clad area | region is multiple layers and the low refractive index reduction prevention layer is provided. In the epitaxial wafer using the conventional AlGaAs type compound semiconductor material, it is sectional drawing of a structure when the 1st clad area | region is multiple layers and the low refractive index prevention layer is not provided. It is the graph which compared the refractive index of the 1st conductivity type 2nd clad area | region and 1st conductivity type current block layer of each structure shown in FIGS. 1 is a cross-sectional view of an epitaxial wafer having an internal stripe structure in a preferred embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Substrate 12 1st conductivity type 2nd cladding region 13 1st conductivity type 1st cladding region 14 Active region 15 2nd conductivity type 1st cladding region 16 1st conductivity type Current block layer 17 2nd conductivity type 1st cladding region 18 Second conductive type contact layer 19 Opening 20 Epitaxial layer 21 First conductive type low refractive index lowering prevention layer 22 Second conductive type low refractive index lowering prevention layer 23 Electrode 31 Second conductive type cap layer 101 n-type GaAs substrate 102 n Type Al _0.52 Ga _0.48 As second cladding region 103 n-type first cladding region 104 consisting of two layers of Al _X0.52 Ga _0.48 As and Al _0.55 Ga _0.45 As Active region 105 Al _0.55 Ga _0.45 As and Al _0.52 Ga _0.48 As p-type first cladding region 106 n-type Al _X0.65 Ga _0.35 As current blocking layer 107 p-type Al _0.52 Ga _0.48 As second cladding region 108 p-type GaAs contact layer 109 openings 201 n-type GaAs composed of two layers of Refractive index prevention layer 202 p-type GaAs lower refractive index prevention layer

Claims (20)

A first conductivity type current having a first conductivity type second cladding region, a first conductivity type first cladding region, an active region, a second conductivity type first cladding region, and a stripe-shaped opening on a substrate. An epitaxial wafer having a block layer, a second conductivity type second cladding region in contact with the first conductivity type current blocking layer inside the opening and at least on both sides of the opening, and a second conductivity type contact layer in this order In
A first conductivity type low refractive index prevention layer and / or the second conductivity type first cladding region and the second conductivity type between the first conductivity type second cladding region and the first conductivity type first cladding region. A second conductivity type low refractive index prevention layer between the second cladding region and
The refractive index of the first conductive type current blocking layer is lower than the refractive index of the second conductive type second cladding region, and the refractive index of the low refractive index reduction preventing layer is the first conductive type second cladding region, the first conductive type. Higher than the refractive index of the first type cladding region, the second conductive type first cladding region, and the second conductive type second cladding region, and / or the first conductive type low refractive index reduction preventing layer and / or the second conductive type low refractive index. An epitaxial wafer characterized in that a thickness prevention layer is thinner than the first conductivity type first cladding region and the second conductivity type first cladding region. A plurality of layers in which at least one selected from the first conductivity type first cladding region, the first conductivity type second cladding region, the second conductivity type first cladding region, and the second conductivity type second cladding region has different refractive indexes. The epitaxial wafer according to claim 1, comprising: The ratio of the thickness and the refractive index of the second conductivity type first cladding region to the first conductivity type first cladding region is 0.9 to 1.1, respectively. Epitaxial wafers. The ratio of the thickness and the refractive index of the second conductivity type second cladding region to the first conductivity type second cladding region is 0.9 to 1.1, respectively. The epitaxial wafer according to claim 1. The ratio of the thickness and refractive index of the second conductive type refractive index lowering prevention layer to the first conductive type refractive index lowering prevention layer is from 0.9 to 1.1. The epitaxial wafer according to any one of the above. The refractive index of the first conductivity type first cladding region, the first conductivity type second cladding region, the second conductivity type first cladding region, and the second conductivity type second cladding region is the first conductivity type current. Higher than the refractive index of the block layer, the refractive index of the first conductive type first cladding region and the first conductive type second cladding region is lower than the refractive index of the first conductive type lower refractive index prevention layer, and 6. The refractive index of the second conductive type first cladding region and the second conductive type second cladding region is lower than the refractive index of the second conductive type low refractive index reduction preventing layer. The epitaxial wafer according to claim 1. At least one of the first conductivity type first cladding region and the second conductivity type first cladding region is composed of a plurality of layers having different refractive indexes, and the refractive index of the layer closest to the active region among the plurality of layers is The epitaxial wafer according to claim 1, wherein the epitaxial wafer has a refractive index lower than that of other layers of the plurality of layers. At least one of the first conductivity type first cladding region and the second conductivity type first cladding region is composed of a plurality of layers having different refractive indexes, and the refractive index of the second conductivity type second cladding region is the first conductivity type. 8. The epitaxial wafer according to claim 7, wherein the epitaxial wafer has a refractive index lower than that of the second cladding region of the mold and lower than a refractive index of a layer other than the layer closest to the active region among the plurality of layers. At least one of the first conductivity type first cladding region and the second conductivity type first cladding region is composed of a plurality of layers having different refractive indexes, and the first conductivity type low refractive index reduction preventing layer and the second conductivity type. The epitaxial wafer according to claim 7 or 8, wherein the thickness of any one of the low refractive index prevention layers is thinner than the thickness of the layer closest to the active region among the plurality of layers. At least one of the first conductivity type first cladding region and the second conductivity type first cladding region is composed of a plurality of layers having different refractive indexes, and a thickness of a layer closest to an active region among the plurality of layers is the plurality of layers. The epitaxial wafer according to claim 7, wherein the epitaxial wafer is thinner than a total thickness of the other layers. At least one of the first conductivity type first cladding region and the second conductivity type first cladding region is composed of a plurality of layers having different refractive indexes, and the first conductivity type second cladding region and / or the second conductivity type. 11. The epitaxial wafer according to claim 7, wherein a refractive index of the second cladding region is higher than a refractive index of a layer closest to the active region among the plurality of layers. The epitaxial wafer according to any one of claims 1 to 11, wherein the second conductivity type low refractive index reduction preventing layer is used as an etching stop layer. A band gap energy in a bulk state of the first conductive type low refractive index lowering prevention layer and / or the second conductive type low refractive index lowering prevention layer is equal to or less than an energy of light oscillated from the active region. The epitaxial wafer according to any one of claims 1 to 12. The first conductive type low refractive index prevention layer and / or the second conductive type low refractive index is reduced by thinning the first conductive type low refractive index prevention layer and / or the second conductive type low refractive index prevention layer. The epitaxial wafer according to claim 13, wherein an effective band gap energy of the rate-inhibiting layer is made larger than light energy oscillated from the active region. The epitaxial wafer according to any one of claims 1 to 14, wherein each of the layers is made of an arsenic III-V compound semiconductor material. The epitaxial wafer according to any one of claims 1 to 14, wherein each of the layers is made of a phosphorus-based III-V group compound semiconductor material. The epitaxial wafer according to any one of claims 1 to 14, wherein each of the layers is made of an arsenic group and a phosphorus group III-V group compound semiconductor material. The epitaxial wafer according to any one of claims 1 to 14, wherein each of the layers is made of a nitride-based III-V group compound semiconductor material. The epitaxial wafer according to any one of claims 1 to 14, wherein each of the layers is made of a II-VI group compound semiconductor material. A semiconductor laser manufactured using the epitaxial wafer according to claim 1.

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