JP2002314199A - Semiconductor laser device and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser device of ridge waveguide type having a structure by which θ// does not vary. SOLUTION: The nitride semiconductor laser device 10 is provided with a multilayer structure comprising an n-AlGaN cladding layer 14, an n-GaN optical guide layer 16, a quantum well activating layer 18, a p-GaN optical guide layer 20, a p-AlGaN cladding layer 22 and a p-GaN contact layer 24 on an n-GaN contact layer 12. Upper layers of the multilayer structure, namely, the p-GaN contact layer 24, the p-AlGaN cladding layer 22 and the p-GaN optical guide layer 20 are formed as a striped ridge 26. The ridge 26 is filled up with an n-GaN filling layer 28 except the uppermost p-GaN contact 24 of the ridge 26, and an electrode 29 on the (p) side is provided on the p-GaN contact 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a buried ridge waveguide type semiconductor laser device and a method of manufacturing the same, and more particularly, to a horizontal far-field image (FFP) at a hetero interface.
The present invention relates to a buried ridge waveguide type semiconductor laser device having a configuration in which the half value width θ _// of the semiconductor laser device does not vary, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Semiconductor laser devices, including GaAs-based and InP-based semiconductor laser devices in a long wavelength region and nitride III-V compound semiconductor laser devices in a short wavelength region, are easy to manufacture. For reasons, air-ridg
e) A ridge waveguide type semiconductor laser device having a structure is widely used in various fields. In a ridge waveguide type semiconductor laser device having an air ridge structure, the upper part of the upper cladding layer and the contact layer are formed as stripe-shaped ridges, and the remaining layers of the upper cladding layer on both sides of the ridge and on both sides of the ridge are covered with an insulating film. This is one of the index guide type (refractive index guided type) semiconductor laser devices that perform mode control based on the resulting difference in the effective refractive index in the lateral direction. A ridge waveguide type nitride III-V compound semiconductor laser device in a short wavelength region (hereinafter, referred to as a nitride semiconductor laser device) has conventionally been used in an air ridge structure for the reason of easy fabrication. Wave type is often used.

Here, the configuration of a nitride-based semiconductor laser device having an air ridge structure will be described with reference to FIG. FIG.
FIG. 1 is a cross-sectional view showing a configuration of a nitride-based semiconductor laser device having an air ridge structure. Nitride based semiconductor laser device 60
Is basically formed on the sapphire substrate 62 via the GaN lateral growth layer 64 as shown in FIG.
GaN contact layer 66, n-AlGaN cladding layer 6
8, MQW active layer 70, p-AlGaN cladding layer 7
2 and a stacked structure of the p-GaN contact layer 74. A GaN substrate may be used instead of a sapphire substrate.

In the laminated structure, the upper layer of the p-AlGaN cladding layer 72 and the p-GaN contact layer 74 are formed as stripe-shaped ridges 76. Also, n
The upper portion of the -GaN contact layer 66, the n-AlGaN cladding layer 68, the MQW active layer 70, and the remaining layer (lower layer) 72a of the p-AlGaN cladding layer 72 are formed as a mesa structure extending in the same direction as the ridge 76. ing. On both sides of the ridge 76 and on the remaining layer 72a of the p-cladding layer 72 on both sides of the ridge 76, an insulating film 78 made of a SiO ₂ film is formed as a current confinement layer. Note that the insulating film 78 also extends as a protective film beside the mesa structure.
A p-side electrode 80 made of a multilayer metal film of Pd / Pt / Au is formed on the insulating film 78, and a p-side electrode 80 is formed through a window of the insulating film 78.
It is in contact with the GaN contact layer 74. Also, n-G
On the aN contact layer 66, an n-side electrode 82 made of a multilayer metal film of Ti / Pt / Au is formed.

[0005]

As the applications of the nitride semiconductor laser device are expanded, the nitride semiconductor laser device has a half width (FFP) of a horizontal far-field image (FFP) at the hetero interface of the resonator structure. The following is referred to as θ _// ). For example, when a nitride-based semiconductor laser device is applied to a light source such as an optical pickup or the like, θ _{// of} 7 degrees or more is required.

[0006] According to the present inventor's study, the results of various experiments to target a nitride semiconductor laser element as described above, theta _//, as shown in FIG. 8, the effective refractive ridge waveguide It was found that it was closely related to the rate difference Δn. In FIG. 8, points showing experimental results are omitted because of complexity. Here, the effective refractive index difference Δn of the ridge waveguide is
As shown in FIG. 7, the difference between the effective refractive index n _eff1 the ridge side of the effective refractive index n _eff2 in the ridge for the oscillation wavelength, n _{ef f1}
−n _eff2 , and according to the study of the present inventor, when the thickness T of the remaining layer (lower layer) 72 a of the p-cladding layer 72 changes, as shown in FIG. , Θ _// change. As described above, in the air ridge structure, the effect of lateral light confinement depends on Δn, that is, when the laser resonator structure has the same layer structure, the thickness of the remaining layer of the upper cladding layer, That is, it depends on the depth of the ridge.

When a ridge is formed by etching a laminated structure of a contact layer, an upper clad layer, etc., A
In an element structure in which an etching stop layer can be provided, such as an lGaInP semiconductor laser element, the ridge depth can be controlled by the etching stop layer, but in the case of a nitride semiconductor laser element, it functions as an etching stop layer. Since an appropriate compound semiconductor layer cannot be found at this stage, an etching stop layer cannot be provided. Therefore, the etching depth when forming the ridge must be controlled by the etching time.

[0008] However, in the control by the etching time,
It is actually very difficult to make the etching depth as designed. For this reason, the nitride-based semiconductor laser device has a problem that the dispersion of θ _// becomes large, and it is difficult to improve the product yield. For example, as can be seen from FIG. 9, in order to suppress the variation of θ _// within ± 0.2 degrees, it is necessary to keep the variation of the etching depth within ± 100 °, but the etching depth is controlled with time. The accuracy of the etching process is not attainable at all.

As a method for controlling lateral light confinement, a structure in which a ridge is buried with an AlGaN layer has been proposed, for example, in Japanese Patent Application Laid-Open No. 9-246651. Here, a typical configuration of a ridge waveguide type semiconductor laser device embedded with an AlGaN layer will be described with reference to FIG. Semiconductor laser device 86 with embedded AlGaN layer
Is a p-GaN contact layer 76 as shown in FIG.
And a ridge 78 consisting of an upper part of the p-AlGaN cladding layer 74 is buried with a current confinement structure layer consisting of an AlGaN layer 88 having an Al composition larger than that of the p-AlGaN cladding layer. It is the same as the system semiconductor laser element 60. Even with the AlGaN layer embedded type, the refractive index of the AlGaN current confinement layer is p-AlGa
Since the refractive index is different from the refractive index of the N cladding layer, the same problem occurs because the lateral light confinement effect depends on the ridge depth similarly to the air ridge structure.

Japanese Patent Laid-Open Publication No. 2000-58461 proposes another method for controlling a lateral light confinement structure. First, as shown in FIG. 11A, in the first growth, n-GaN is deposited on a sapphire substrate (not shown).
The contact layer 92, the n-AlGaN cladding layer 93, the active layer 94, and a part 95 of the p-AlGaN cladding layer are grown. Then, as shown in FIG. 11B, a mask 96 of an SiO ₂ film covering the current confinement region is formed with p-AlGa.
As shown in FIG.
As shown in (c), a method of growing the remaining p-AlGaN cladding layer 97 and p-GaN contact layer 98 has been proposed. In this case, although the lateral light confinement structure is stable and θ _// is stable,
Since the most growing interface exists in the region where the current density is highest in the semiconductor laser device, there is a big problem that it is difficult to extend the life of the laser.

As described above, a nitride-based semiconductor laser device having a configuration in which θ _// does not vary has not been realized so far. In the above description, the problem of the variation of θ _// was described using a nitride-based semiconductor laser device as an example.
This is a problem that applies to all semiconductor laser devices such as a semiconductor laser device and an AlGaN semiconductor laser device. Accordingly, an object of the present invention is to provide a ridge waveguide type semiconductor laser device having a configuration in which θ _// does not vary, and a method of manufacturing the same.

[0012]

The present inventors embed a ridge in a current confinement layer from a compound semiconductor layer having the same refractive index as the remaining layer of the compound semiconductor layer etched when forming the ridge and having a different conductivity type. Accordingly, the inventors have conceived of making θ _// constant without depending on the thickness of the remaining layer, and have come to invent the present invention through repeated experiments.

In order to achieve the above object, based on the above findings, a semiconductor laser device according to the present invention is a ridge waveguide type semiconductor laser device in which a ridge formed on an active layer is buried with a buried layer. An upper cladding layer formed in the ridge, an upper layer extending below the upper cladding layer in the ridge, and a lower layer extending above the active layer beside the ridge, and are the same as the upper cladding layer. A light guide layer made of a conductive type compound semiconductor layer, wherein the buried layer is a current constriction layer of the same conductivity type as the light guide layer and having a different refractive index.

In the present invention, the ridge is buried with a current confinement layer made of a compound semiconductor layer having the same refractive index as the lower layer (remaining layer) of the compound semiconductor layer etched when forming the ridge and having a different conductivity type. Since the effective refractive index difference Δn between the inside of the ridge and the side of the ridge is constant without depending on the film thickness of the remaining layer of the light guide layer, θ _// is constant. The shape of the ridge is not limited, and may be, for example, a stripe, a flare, or a taper.

Another semiconductor laser device according to the present invention is a light guide layer, a first upper clad layer provided on the light guide layer and having the same conductivity type as the light guide layer, and a first upper clad layer on the first upper clad layer. And a compound semiconductor layer having the same conductivity type and the same composition as the light guide layer and a second upper cladding layer provided on the compound semiconductor layer and having the same conductivity type as the light guide layer. The upper part of the compound semiconductor layer and the second upper clad layer are formed as ridges, and the lower part of the compound semiconductor layer forms a surface layer beside the ridge, and the ridges are mutually connected at the same refractive index as the light guide layer. It is characterized by being buried with buried current constriction layers of different conductivity types. Accordingly, when the light guide layer is etched to form the ridge, even if over-etching is performed, the active layer is not damaged because the compound semiconductor layer is interposed on the active layer.

In a further preferred embodiment of the present invention, the buried layer extends on the lower layer (remaining layer) of the light guide layer, burying the ridge up to the upper surface of the ridge. This makes it easier to form the buried layer uniformly. Further, an electrode in contact with the upper surface of the ridge extends on the buried layer via a layer having a different conductivity type from that of the buried layer. Thereby, the contact area of the electrode is increased, and the driving voltage can be reduced.

A method of manufacturing a semiconductor laser device according to the present invention is a method of manufacturing a ridge waveguide type semiconductor laser device in which a stripe-shaped ridge formed on an active layer is buried with a burying layer. A growth step of growing a compound semiconductor layer including an optical guide layer and then an upper clad layer, etching the compound semiconductor layer including the upper clad layer and the upper part of the light guide layer to form a ridge, and forming a light guide beside the ridge. The method is characterized by including a step of extending the remaining layer of the layer and a burying step of burying the ridge with a burying layer having the same refractive index as that of the light guide layer and different in conductivity type.

Preferably, in the growing step, a compound semiconductor layer of the same conductivity type and the same composition as the light guide layer and a compound semiconductor layer of the same conductivity type and the same composition as the upper cladding layer are sequentially grown on the active layer. Then, a compound semiconductor layer including a light guide layer and an upper clad layer is grown.

[0019]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Embodiment 1 This embodiment is an example of an embodiment of a nitride-based III-V compound semiconductor laser device (hereinafter, referred to as a nitride-based semiconductor laser device) according to the present invention. FIG. 2 is a cross-sectional view illustrating a configuration of a main part of the nitride-based semiconductor laser device according to the embodiment. As shown in FIG. 1, the nitride-based semiconductor laser device 10 of the present embodiment includes an n-GaN contact layer 12, an n-AlGaN cladding layer 14, a sapphire substrate, a GaN lateral growth layer, and the like, not shown. n-GaN
The light guide layer 16, the quantum well active layer 18, the p-GaN light guide layer 20, the p-AlGaN cladding (Al composition is 7
%) Layer 22 and a p-GaN contact layer 24. p-GaN optical guide layer 20, p-Al
GaN cladding layer 22 and p-GaN contact layer 24
Are 0.20 μm, 0.5 μm, and 0.1 μm, respectively. The thicknesses of the layers below the active layer 18 are the same as in the conventional case.

The p-GaN contact layer 24, the p-AlGaN cladding layer 22, and the p-GaN
The upper layer of the light guide layer 20 is formed as a stripe-shaped ridge 26, and a lower layer (remaining layer) 20 a of the p-GaN light guide layer 20 extends on the active layer 18 beside the ridge 26. The ridge 26 is buried with an n-GaN buried layer 28 except for the p-GaN contact 24 above the ridge 26, and a p-side electrode 29 is provided on the p-GaN contact 24.

In the nitride semiconductor laser device 10 of this embodiment, in the ridge 26, the p-AlGaN layers each having a predetermined thickness on the active layer 18 are formed.
The clad layer 22 and the p-GaN light guide layer 20 form a laminated structure. On the other hand, beside the ridge 26, the active layer 1
8 has a p-Ga
Even if the etching depth of the N light guide layer 20 fluctuates, the N light guide layer 20 is formed of a GaN layer having a predetermined thickness and the same refractive index. Therefore, in the nitride-based semiconductor laser device 10 of this embodiment, as long as θ _// does not vary, and as long as the remaining layer 20 a of the p-GaN optical guide layer 20 remains on the ridge 26 side, the active layer 18 is not damaged by etching, so that good laser characteristics can be exhibited.

Embodiment of the Method of Fabricating a Semiconductor Laser Device This embodiment is an example of an embodiment in which the method of fabricating a semiconductor laser device according to the present invention is applied to the fabrication of the nitride-based semiconductor laser device 10 described above. 2 (a) to FIG.
(C) is a sectional view of each step when the nitride-based semiconductor laser device 10 is manufactured according to the method of the present embodiment. First, as shown in FIG. 2A, a MOC is placed on a sapphire substrate (not shown), a GaN lateral growth layer, and the like.
By the VD method, the n-GaN contact layer 12,
n-AlGaN cladding layer 14, n-GaN light guide layer 16, quantum well active layer 18, p-GaN light guide layer 2
The p-AlGaN cladding layer 22 and the p-GaN contact layer 24 are epitaxially grown to form a stacked structure.

Next, by dry etching, p
As shown in FIG. 2B, the upper portions of the -GaN contact layer 24, the p-AlGaN cladding layer 22, and the p-GaN optical guide layer 20 are etched to form a ridge 26 and a p-side beside the ridge 26. -The lower layer (remaining layer) 20 a of the GaN light guide layer 20 is left on the active layer 18. Subsequently, as shown in FIG. 2C, the ridge 26 is buried by epitaxially growing the n-GaN buried layer 28 at a growth temperature of about 600 ° C. Further, by forming the p-side electrode 29 and the like, the nitride-based semiconductor laser device 10 shown in FIG. 1 can be manufactured.

Using the nitride-based semiconductor laser device 10 of this embodiment as a sample, θ _// was measured while changing the thickness of the remaining layer 20 a of the p-GaN optical guide layer 20 beside the ridge 26. As shown in the figure, the thickness T (μm) of the remaining layer 20a
There also vary, theta _// it has been demonstrated to maintain the 8.7 degrees theta _// hardly changes.

Example 1 This example is a specific example of the first embodiment, and each compound semiconductor layer is formed with the following film thickness and carrier concentration. In the first embodiment, the p-GaN contact layer 24 and the p-GaN
The etching amount of the upper portions of the AlGaN cladding layer 22 and the p-GaN light guide layer 20 is 0.54 μm. p-GaN optical guide layer 20: ridge inner film thickness is 2000Å thickness of remaining layer 20a beside ridge 1500１ carrier concentration 1 × 10 ¹⁸ cm ^-3 p-AlGaN cladding layer 22: Al composition 7% film thickness 0.5 μm carrier Concentration 1 × 10 ¹⁸ cm ⁻³ p-GaN contact 24: 0.1 μm in thickness Carrier concentration 2 × 10 ¹⁸ cm ⁻³ n-GaN buried layer 28: On the remaining layer 20 a of the p-GaN optical guide layer 20 beside the ridge Thickness 0.3 μm Carrier concentration 1 × 10 ¹⁸ cm ⁻³ θ _// : 9.0 °

Embodiment 2 This embodiment is another example of the embodiment of the nitride semiconductor laser device according to the present invention. FIG. 4 shows the structure of the nitride semiconductor laser device of this embodiment. It is sectional drawing which shows a structure. The nitride semiconductor laser device 30 of the present embodiment is
As shown in FIG. 4, p-AlGaN cladding layer has p-AlGaN cladding layer.
Except for the presence of the GaN layer 32, the structure is the same as that of the nitride-based semiconductor laser device 10 of the first embodiment, and the same effects as the first embodiment can be obtained. In the nitride-based semiconductor laser device 30 of the present embodiment, the p-AlGaN layer 34 and the p-GaN
Since the layer 32 is present, p-Ga
Even if the N light guide layer 20 is over-etched, the quantum well active layer 18 will not be damaged.

Example 2 This example is a specific example of Embodiment 2 and each compound semiconductor layer is formed with the following film thickness and carrier concentration. p-GaN layer 32: thickness 1000 ° Carrier concentration 1 × 10 ¹⁸ cm ⁻³ p-AlGaN layer 34: Al composition 7% film thickness 0.05 μm Carrier concentration 1 × 10 ¹⁸ cm ⁻³ θ _// : 8.5 ° The thickness, carrier concentration, and the like of the p-GaN optical guide layer 20, the p-AlGaN cladding layer 22, the p-GaN contact 24, and the p-GaN buried layer 28 are the same as those in the first embodiment.

Embodiment 3 This embodiment is still another example of the embodiment of the nitride-based semiconductor laser device according to the present invention. FIG. 5 shows the nitride-based semiconductor laser device of this embodiment. It is sectional drawing which shows a structure. The nitride-based semiconductor laser device 40 of this embodiment is
This is a modification of the first embodiment, and as shown in FIG.
-A 0.1 μm-thick p-G film is formed on the GaN buried layer 28.
Except that the aN layer 42 is formed as a contact layer, the nitride-based semiconductor laser device 10 of the first embodiment is
It has the same configuration as. In this embodiment, n-Ga
Since the p-GaN layer 42 is provided on the N buried layer 28, the contact area of the p-side electrode 29 increases, and the contact resistance decreases, so that the operating voltage of the nitride-based semiconductor laser device 40 decreases.

Embodiment 4 This embodiment is still another example of the embodiment of the nitride semiconductor laser device according to the present invention. FIG. 6 shows the structure of the nitride semiconductor laser device of this embodiment. It is sectional drawing which shows a structure. The nitride-based semiconductor laser device 50 of the present embodiment is
In another modification of the first embodiment, as shown in FIG. 6, an n-GaN buried layer 52 extends on the active layer 18 with the same thickness as the ridge height of the ridge 26. n-Ga
In the crystal growth of the N buried layer, the GaN layer has a tendency to grow in the lateral direction. Therefore, in this embodiment, the n-GaN buried layer 52 is grown at 1000 ° C. until the laterally grown portion S becomes 3 μm or more. Is grown with the same thickness as the ridge height of the ridge 26, so that a buried layer that is stable in shape can be formed. In the present embodiment, a modification of the first embodiment is described as an example.
This can be easily applied not only to the first embodiment but also to the first to third embodiments.

[0030]

According to the present invention, the ridge formed by the upper cladding layer and the upper layer of the light guide layer is buried in the current confinement layer of the same refractive index as the light guide layer and of a different conductivity type. Even if the etching depth of the light guide layer at the time of forming the ridge varies somewhat, the effective refractive index difference between the inside of the ridge and the ridge side is independent of the thickness of the lower layer (remaining layer) of the light guide layer. Since Δn is constant, θ _// is constant. Further, the film thickness distribution in the wafer plane can be absorbed to some extent. As a result, the product yield is improved. Furthermore,
Unlike the conventional case, θ _// can be stabilized without forming a regrowth interface in the current injection region, so that the device life is improved. In filling the ridge, the buried layer is grown so that the buried layer that has grown to the upper surface of the ridge extends above the lower layer of the optical guide layer, and the thickness distribution of the buried layer near the ridge is made uniform. In addition, the stability of burying growth of the burying layer is improved. By lowering the contact resistance of the p-side electrode by extending an electrode in contact with the upper surface of the ridge, for example, a p-side electrode, on the buried layer via a compound semiconductor layer having a different conductivity type from the buried layer, for example, a p-type layer, The drive voltage of the semiconductor laser device can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a nitride-based semiconductor laser device according to a first embodiment.

FIGS. 2A to 2C are cross-sectional views of respective steps when manufacturing a nitride-based semiconductor laser device according to the method of the embodiment.

FIG. 3 is a graph showing the relationship between the thickness T (μm) of the remaining layer and θ _// of the nitride-based semiconductor laser device of the first embodiment.

FIG. 4 is a cross-sectional view illustrating a configuration of a nitride-based semiconductor laser device according to a second embodiment.

FIG. 5 is a cross-sectional view illustrating a configuration of a nitride-based semiconductor laser device according to a third embodiment.

FIG. 6 is a cross-sectional view illustrating a configuration of a nitride-based semiconductor laser device according to a fourth embodiment.

FIG. 7 is a sectional view showing a configuration of a nitride-based semiconductor laser device having an air ridge structure.

FIG. 8 is a graph showing a relationship between an effective refractive index difference Δn and θ _// .

FIG. 9 is a graph showing the relationship between the thickness T of the remaining layer (lower layer) of the p-cladding layer and θ _// .

FIG. 10 is a sectional view showing a configuration of a nitride-based semiconductor laser device of an embedded AlGaN layer type.

FIGS. 11A to 11C are cross-sectional views showing steps of forming a lateral light confinement structure.

[Explanation of symbols]

10... The nitride-based semiconductor laser device of Embodiment 1
2 ... n-GaN contact layer, 14 ... n-AlGa
N cladding layer, 16 n-GaN light guiding layer 18
Quantum well active layer, 20... P-GaN optical guide layer, 22
... p-AlGaN cladding layer, 24 ... p-GaN contact layer, 26 ... stripe ridge, 28 ... n
-GaN buried layer, 29 ... p-side electrode, 30 ... nitride-based semiconductor laser device of embodiment 2, 32 ... p-G
aN layer, 34... p-AlGaN layer, 40... nitride semiconductor laser device of Embodiment 3, 42... p-GaN
Layer: 50: Nitride-based semiconductor laser device of Embodiment 4; 52: N-GaN buried layer; 60: Nitride-based semiconductor laser device of air ridge structure; 62: Sapphire substrate; GaN lateral growth layer, 66 ... n-
GaN contact layer, 68 n-AlGaN clad layer, 70 MQW active layer, 72 p-AlGaN clad layer, 74 p-GaN contact layer, 76
Striped ridge, 78 insulating film, 80 p-side electrode, 82 n-side electrode, 86 AlGaN layer embedded semiconductor laser device, 88 AlGaN layer, 92
... n-GaN contact layer, 93 ... n-AlGaN cladding layer, 94 ... active layer, 95 ... p-AlGaN cladding layer, 96 ... mask, 97 ... p-AlGaN cladding layer, 98 ... p- GaN contact layer.

Continuation of the front page (72) Inventor Shiro Uchida 3-53-3 Shiratori, Shiroishi-shi, Shiroishi-shi, Miyagi F-term (reference) in Sony Shiroishi Semiconductor Co., Ltd. 5F073 AA21 AA45 AA74 BA04 CA07 DA05 EA19

Claims (10)

[Claims] 1. A ridge waveguide type semiconductor laser device in which a ridge formed on an active layer is buried with a buried layer, wherein the ridge waveguide has an upper cladding layer formed in the ridge and extends below the upper cladding layer in the ridge. A light guide layer comprising a compound semiconductor layer of the same conductivity type as the upper clad layer, the light guide layer having an upper layer and a lower layer extending on the active layer beside the ridge. A semiconductor laser device comprising a current constriction layer having the same refractive index as that of the above and a different conductivity type or a high resistance even with the same conductivity type. 2. The ridge according to claim 1, wherein the ridge has one of a stripe shape, a flare shape, and a tapered shape.
3. The semiconductor laser device according to item 1. 3. The semiconductor laser device according to claim 1, wherein the buried layer is a compound semiconductor layer having the same composition as that of the light guide layer and having different conductivity types. 4. The semiconductor laser device according to claim 1, wherein the buried layer is a high-resistance compound semiconductor layer having the same composition as the light guide layer and the same conductivity type. 5. A light guide layer, a first upper clad layer provided on the light guide layer and having the same conductivity type as the light guide layer, and provided on the first upper clad layer and the same as the light guide layer. A conductive semiconductor layer having the same composition and a second upper clad layer provided on the compound semiconductor layer and having the same conductivity type as the light guide layer, provided on the active layer; The upper and second upper cladding layers are formed as ridges, and the lower portion of the compound semiconductor layer forms a surface layer beside the ridge, and the ridge has the same refractive index as the optical guide layer and has a different conduction type buried current constriction. A semiconductor laser device embedded in a layer. 6. The semiconductor laser device according to claim 1, wherein the buried layer extends over the lower layer of the light guide layer by burying the ridge up to the upper surface of the ridge. 7. The electrode according to claim 1, wherein the electrode in contact with the upper surface of the ridge extends on the buried layer via a compound semiconductor layer having a conductivity type different from that of the buried layer.
The semiconductor laser device according to any one of the above items. 8. A method of manufacturing a ridge waveguide type semiconductor laser device in which a stripe-shaped ridge formed on an active layer is buried with a buried layer, comprising a light guide layer, and then an upper clad layer on the active layer. A growth step of growing a compound semiconductor layer; a compound semiconductor layer including an upper cladding layer; and a step of etching the upper portion of the light guide layer to form a ridge, and extending the remaining layer of the light guide layer beside the ridge. A burying step of burying the ridge with a buried layer having the same refractive index as the light guide layer and having a different conductivity type from each other. 9. In the growing step, a compound semiconductor layer having the same conductivity type and the same composition as the optical guide layer and a compound semiconductor layer having the same conductivity type and the same composition as the upper cladding layer are sequentially grown on the active layer. 9. The method according to claim 8, wherein a compound semiconductor layer including an optical guide layer and an upper clad layer is subsequently grown. 10. The burying layer according to claim 8, wherein in the burying step, the burying layer is grown such that the burying layer extending on the remaining layer of the light guide layer grows to the upper surface of the ridge. A method for manufacturing a semiconductor laser device.