JPH11168261A - Semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser device which is low in oscillation threshold value, high in oscillation efficiency and reliability, long in service life, and stable in oscillation wavelength. SOLUTION: An N-GaAs buffer layer 2, an N-AlGaAs clad layer 3, a non- doped InGaAs active layer 4, a P-Alx Ga1-x As clad layer 6, and a P-GaAs contact layer 7 are successively formed on an N-GaAs substrate 1, wherein an N-AlGaAs current block layer 5 with a stripe-like window is buried in the clad layer 6. A diffraction grating 10 possessed of periodic irregularities is formed on the active layer-side interface of the current block layer 5, and no diffraction grating is present in a stripe-like window 11 or a current injection region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a distributed feedback semiconductor laser device.

[0002]

2. Description of the Related Art Conventionally, semiconductor lasers have been widely used as light sources for optical recording devices, solid-state laser excitation, and optical communication. Among them, distributed feedback type (DFB: Distributed Fe
The semiconductor laser forms a diffraction grating by providing periodic irregularities in an optical waveguide in the semiconductor laser, and achieves wavelength stabilization by utilizing a feedback effect of light by the diffraction grating. Since such a DFB laser oscillates in a stable single mode, the longitudinal mode hopping phenomenon caused by a temperature change does not occur, and the mode hopping noise seen in a normal Fabry-Perot semiconductor laser does not occur. It is excellent as a light source that requires a noise level. In addition, the DFB laser has excellent characteristics such as a small change in temperature of the oscillation wavelength and a choice of the oscillation wavelength by changing the period of the diffraction grating.
It is also suitable for purposes such as a light source for optical communication and an excitation light source for a solid-state laser.

FIG. 6 shows an example of a conventional DFB laser.
FIG. 6A is an overall perspective view, and FIG. 6B is a partial perspective view showing the shape of the diffraction grating. This DFB laser is described in Japanese Patent Application Laid-Open No. Sho 60-66484, and is sequentially formed on an n-type (hereinafter referred to as n-) GaAs substrate 102.
n-Al _0.40 Ga _0.60 As clad layer 103, non-doped Al _0.10 Ga _0.90 As active layer 104, p-type (hereinafter referred to as p-type)
-) Al _0.25 Ga _0.75 As light guide layer 105, n-GaAs current blocking layer 106 having a striped window,
p-Al _0.40 Ga _0.60 As clad layer 107, p-Ga
An As contact layer 108 is formed, and electrodes 101 and 109 are formed on the lower surface of the substrate 102 and the upper surface of the contact layer 108.
Are formed.

[0006] As shown in FIG.
5, diffraction gratings 112 and 113 having periodic irregularities are formed on a portion 111 that becomes the bottom of the striped window on the upper surface of the strip 5 and on the upper surface of the current blocking layer 106, respectively. A cladding layer 107 is formed on these diffraction gratings 112 and 113 so as to fill the stripe-shaped window.

[0005]

The conventional DF shown in FIG.
In a B laser, current is injected into the active layer 104 through a striped window in the current blocking layer 106. Therefore, a diffraction grating is also formed in the portion 111 of the light guide layer 105 which is the bottom of the striped window, that is, in the current injection region.

However, in a process such as etching at the time of fabricating a diffraction grating, the crystal surface is exposed to the air and the like, so that the substrate surface is oxidized and a large number of crystal defects are generated. Crystal defects are concentrated just above the portion 104, and a portion having poor crystallinity exists.

In such a semiconductor laser, during operation,
Existing crystal defects tend to trigger and increase the crystal defects further, resulting in an extremely short life. In addition, the internal loss in the laser resonator increases, causing problems such as an increase in oscillation threshold and a decrease in efficiency.

An object of the present invention is to provide a semiconductor laser device which has high oscillation efficiency at a low oscillation threshold, high reliability, long life, and has a stable oscillation wavelength.

[0009]

According to the present invention, a pair of cladding layers having a forbidden band width greater than or equal to the forbidden band width of the active layer are provided on both sides of the active layer, and a stripe is formed on one of the cladding layers. In a self-aligned semiconductor laser device in which a current block layer having a shaped window is embedded, an interface of the current block layer or between the interface and the active layer, in a region excluding a striped window, A semiconductor laser device comprising a diffraction grating for controlling an oscillation wavelength.

According to the present invention, when a voltage is applied to the semiconductor laser, carriers are injected and are blocked by the current blocking layer when passing through the cladding layer. Therefore, the carriers pass only through the portion where the current blocking layer does not exist, that is, only through the stripe-shaped groove portion. Carriers injected into the active layer recombine and radiate light. As the level of the injected current increases, stimulated emission starts, and eventually laser oscillation occurs. Part of the laser light oozes to the lower part of the current blocking layer and is guided.

A diffraction grating for stabilizing the oscillation wavelength is formed below the current blocking layer. As a diffraction grating, a) one having periodic irregularities formed at an interface (one or both of a lower interface and an upper interface) of a current blocking layer,
b) A grating layer formed between the active layer-side interface and the active layer can be used.

Here, the period の of the periodic unevenness formed below the current block layer or the period す る in which the width of the grating layer changes 設定 is set so as to satisfy the following equation (1).

Λ = m · λo / (2 · nr) (1) where m is an integer of 1 or more (1, 2, 3,...), Nr is the refractive index of the optical waveguide, and λo is the oscillation wavelength. . By satisfying this diffraction condition, only light having the wavelength λo is selected, and a single mode oscillation is obtained.

Further, according to the present invention, the diffraction grating is formed only in the region excluding the stripe-shaped window. Since the diffraction grating does not exist in the current injection region through which the current passes, crystal defects occur in this region. Not. Therefore, the possibility that problems such as an increase in the oscillation threshold value and a decrease in the oscillation efficiency are extremely reduced. In addition, a decrease in reliability due to growth of crystal defects can be suppressed.

Further, according to the present invention, an optical waveguide layer having a forbidden band width equal to or larger than the forbidden band width of the active layer is provided on one side or both sides of the active layer, and the active layer and the optical waveguide layer are sandwiched therebetween.
A self-aligned semiconductor laser in which a pair of cladding layers each having a forbidden band width equal to or larger than the forbidden band width of the optical waveguide layer is provided, and a current blocking layer having a stripe-shaped window is embedded in at least one of the cladding layers. In the device,
A semiconductor laser, wherein a diffraction grating for controlling an oscillation wavelength is formed in an interface of the current blocking layer or between the interface and the active layer and excluding a stripe-shaped window. Device.

According to the present invention, by providing an optical waveguide layer on one side or both sides of the active layer, light generated in the active layer is guided by the optical waveguide layer, so that light concentration on the active layer is avoided. As a result, higher output and longer life of the laser can be achieved.

Further, according to the present invention, the diffraction grating is formed only in the region excluding the stripe-shaped window. Since the diffraction grating does not exist in the current injection region through which the current passes, crystal defects occur in this region. Not. Therefore, the possibility that problems such as an increase in the oscillation threshold value and a decrease in the oscillation efficiency are extremely reduced. In addition, a decrease in reliability due to growth of crystal defects can be suppressed.

Further, according to the present invention, a pair of optical waveguide layers each having a forbidden band width equal to or larger than the forbidden band width of the active layer is provided on both sides of the active layer, and the active layer and the optical waveguide layer are sandwiched therebetween. A pair of cladding layers each having a forbidden bandwidth equal to or greater than the forbidden band width of the optical waveguide layer are provided, and between the active layer and the optical waveguide layer, each of the active layer and each of the forbidden bandwidths of the optical waveguide layer or greater. In a self-aligned semiconductor laser device in which a carrier block layer having a forbidden band width is provided and a current block layer having a stripe-shaped window is embedded in at least one of the optical waveguide layers, an interface of the current block layer or the A semiconductor laser device characterized in that a diffraction grating for controlling an oscillation wavelength is formed in a region between an interface and an active layer, excluding a striped window.

According to the present invention, when a voltage is applied to the semiconductor laser, carriers (electrons and holes) are injected and are blocked by the current blocking layer when passing through the optical waveguide layer.
Therefore, the carriers pass only through the portion where the current blocking layer does not exist, that is, only through the stripe-shaped groove portion.
The carriers injected into the active layer recombine and emit light,
As the injection current level increases, stimulated emission begins,
Eventually, laser oscillation occurs. Part of the laser light oozes to the lower part of the current blocking layer and is guided. On the other hand, the carriers in the active layer are confined in the active layer by the presence of the carrier block layer, so that the recombination efficiency is improved.

A diffraction grating for stabilizing the oscillation wavelength is formed below the current block layer. As a diffraction grating, a) one having periodic irregularities formed at an interface (one or both of a lower interface and an upper interface) of a current blocking layer,
b) A grating layer formed between the active layer-side interface and the active layer can be used. Here, a single mode oscillation can be obtained by setting the period of the periodic unevenness {or the period at which the width of the grating layer changes} so as to satisfy the above equation (1).

Further, in the present invention, the diffraction grating is formed only in the region excluding the stripe-shaped window. Since the diffraction grating does not exist in the current injection region through which the current passes, crystal defects occur in this region. Not. Therefore, the possibility that problems such as an increase in the oscillation threshold value and a decrease in the oscillation efficiency are extremely reduced. In addition, a decrease in reliability due to growth of crystal defects can be suppressed.

By providing the carrier block layer between the active layer and the optical waveguide layer, the waveguide mechanism in the device can be freely designed independently of the confinement of carriers in the active layer. Therefore, the adoption of a wide optical waveguide layer makes it possible to make the waveguide mode closer to an ideal Gaussian type. As a result, the refractive index and thickness of the diffraction grating can be selected in a wide range, so that the degree of freedom in design is increased, the manufacturing margin is widened, and the manufacturing yield of the semiconductor laser is improved. On the other hand, in the case where the carrier block layer is not provided between the active layer and the optical waveguide layer, the waveguide mode becomes a Mt. Fuji type having a sharp peak. On the other hand, when a carrier block layer is provided between the active layer and the optical waveguide layer,
The waveguide mode is a Gaussian type having a shape in which the shoulder is overhanged compared to the Mt. Fuji type, and changes in the electric field intensity become more gradual in a portion where the electric field intensity is large. Therefore, in a semiconductor laser having a Gaussian waveguide mode, even if a diffraction grating for controlling the wavelength is formed at a position distant from the active layer, the diffraction grating functions sufficiently and the electric field intensity changes. Even if the distance and the refractive index distribution between the active layer and the diffraction grating are slightly changed in the manufacturing process due to the gradual effect, the influence can be reduced and the manufacturing yield of the element can be improved. .

Further, according to the present invention, the semiconductor material forming the optical waveguide layer is made of GaAs or Al having an Al composition of 0.3 or less.
It is characterized by being made of GaAs, InGaP, or InGaAsP.

According to the present invention, in a process for forming a diffraction grating for stabilizing an oscillation wavelength, an optical waveguide layer exposed to the atmosphere is made of a material having a small oxidation deterioration, that is, a material having a low Al composition ratio or Al. It is formed of a material that does not contain. Therefore, oxidation of the region where the diffraction grating is formed or the surface exposed to the atmosphere in the stripe portion is suppressed, the crystallinity of each layer to be regrown is improved, and a highly reliable semiconductor laser can be obtained. Here, the composition ratios of the respective elements of InGaP and InGaAsP may be any as long as they can achieve lattice matching with the substrate.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following embodiments, a diffraction grating is manufactured by etching a layer forming a diffraction grating by using a resist in which a grating is formed by a well-known interference exposure method as a mask. . That is, when a layer for forming a diffraction grating is grown, a resist is applied, the resist is exposed to a grating shape by interference exposure of a laser beam, developed, and the lower layer is etched to a predetermined depth using the resist as a mask. After removing the mask resist, the upper layer was subsequently grown. In this step, the layer forming the diffraction grating is exposed to the atmosphere.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention. FIG. 1 (a) is an overall perspective view, and FIG. 1 (b) is a partial perspective view showing the shape of a diffraction grating. This semiconductor laser device is configured as a DFB laser and has n-GaAs
N-GaAs (thickness t =
0.5 μm), n-AlGaAs
(Al composition ratio x = 0.4, t = 1.5 μm) clad layer 3, non-doped GaAs well layer (t = 0.00
8 μm) / non-doped AlGaAs barrier layer (x = 0.
2, t = 0.005 μm) double quantum well active layer 4, p-AlGaAs (x = 0.4, t = 1.6 μm)
Clad layer 6 made of p-GaAs (t = 1.0 μm)
m) is formed using MOCVD (metal organic chemical vapor deposition) or the like, and n-AlGaAs having a stripe-shaped window in the cladding layer 6 is formed.
The current block layer 5 (x = 0.5, t = 0.1 μm) is embedded. Electrodes 9 and 8 are formed on the lower surface of the substrate 1 and the upper surface of the contact layer 7, respectively.

The AlGaAs-based material tends to increase the forbidden band width as the Al composition increases. In the present embodiment, the forbidden band width of the cladding layer is larger than the forbidden band width of the active layer 4.

As shown in FIG. 1B, a diffraction grating 10 having a periodic uneven shape is formed at the interface of the current blocking layer 5 on the active layer side, and is formed in a stripe shape without the current blocking layer 5. No diffraction grating exists in the window portion 11, ie, the current injection region. The current blocking layer 5 is formed on the diffraction grating 10, and the cladding layer 6 is formed so as to fill the window 11.

Next, the operation will be described. When a positive bias voltage is applied to the electrode 8 of the contact layer 7 and a negative bias voltage is applied to the electrode 9 of the substrate 1, a current flows from the contact layer 7 toward the substrate 1, and a region where the current blocking layer 5 does not exist, that is, a stripe-shaped window By passing only the part 11, the current density increases.

A current is injected into the active layer 4 as a carrier, and radiates light by carrier recombination. Furthermore, as the amount of injected current is increased, stimulated emission starts, and eventually leads to laser oscillation. The laser light oozes into the cladding layers 3 and 6 on both sides of the active layer 4, oozes out into the lower part of the current blocking layer 5, and is guided.

Here, the period Λ of the diffraction grating 10 is given by the following equation (1).
Is satisfied so that only the wavelength λo selectively oscillates, and as a result, a single mode oscillation is obtained. At this time, in the window 11 which is a current injection region,
Since there is no deterioration in crystallinity, a DFB semiconductor laser having a low oscillation threshold, high efficiency, and long life can be realized.

(Second Embodiment) FIG. 2 is a perspective view showing a second embodiment of the present invention. This semiconductor laser device
It is configured as a DFB laser, and n-GaAs (thickness t = 0.5 μm) is sequentially formed on a substrate 21 made of n-GaAs.
m), n-AlGaAs (Al
A cladding layer 23 having a composition ratio x = 0.45, t = 1.5 μm) and a non-doped AlGaAs well layer (x = 0.
1, t = 0.006 μm) / AlGaAs barrier layer (x
= 0.3, t = 0.005 μm), the p-AlGaAs (x = 0.3, t = 0.
15 μm), the first cladding layer 25 comprising p-AlGa
Second cladding layer 27 made of As (x = 0.55, t = 1.0 μm), contact layer 28 made of p-GaAs
Is formed using MOCVD (metal organic chemical vapor deposition) or the like, and the first clad layer 25 and the second clad layer 2 are formed.
7, n-AlGa having a striped window
A current blocking layer 26 made of As (x = 0.58, t = 0.1 μm) is embedded. Electrodes 30 and 29 are formed on the lower surface of the substrate 21 and the upper surface of the contact layer 28, respectively.

Here, the first cladding layer 25 is formed of the active layer 2
4 functions as an optical waveguide layer for guiding the light generated. In addition, the band gap of AlGaAs-based materials tends to increase as the Al composition increases. In the present embodiment, the forbidden band width of the first cladding layer 25 is larger than the forbidden band width of the active layer 24, and the cladding layer 23 and the second cladding layer 27 above the first cladding layer 25 are lower than the first cladding layer 25. The forbidden band is larger.

At the interface of the current blocking layer 26 on the active layer side,
A diffraction grating 31 having a periodic uneven shape is formed, and the diffraction grating does not exist in the striped window portion 11 where the current blocking layer 26 does not exist, that is, in the current injection region.

Next, the operation will be described. When a positive bias voltage is applied to the electrode 29 of the contact layer 28 and a negative bias voltage is applied to the electrode 30 of the substrate 21, a current flows from the contact layer 28 toward the substrate 21, a region where the current blocking layer 26 does not exist,
That is, the current density is increased by passing through only the striped window 11.

A current is injected into the active layer 24 as a carrier, and radiates light by carrier recombination. Furthermore, as the amount of injected current is increased, stimulated emission starts, and eventually leads to laser oscillation. The laser light oozes into the cladding layer 23 and the first cladding layer 25 on both sides of the active layer 24 and also oozes out below the current blocking layer 26 and is guided.

Here, the period Λ of the diffraction grating 31 is given by the following equation (1).
Is satisfied so that only the wavelength λo selectively oscillates, and as a result, a single mode oscillation is obtained. At this time, in the window 11 which is a current injection region,
Since there is no deterioration in crystallinity, a DFB semiconductor laser having a low oscillation threshold, high efficiency, and long life can be realized.

(Third Embodiment) FIG. 3 is a perspective view showing a third embodiment of the present invention. This semiconductor laser device
The substrate is configured as a DFB laser, and n-GaAs (thickness t = 0.5 μm) is sequentially formed on a substrate 41 made of n-GaAs.
m), n-AlGaAs (Al
A cladding layer 43 having a composition ratio x = 0.24, t = 1.1 μm, n-AlGaAs (x = 0.2, t = 0.8)
8 μm), n-AlGaAs (x
= 0.5, t = 0.02 μm), non-doped InGaAs well layer (In composition ratio y = 0.2, t = 0.008 μm) / non-doped AlG
aAs barrier layer (Al composition ratio x = 0.2, t = 0.00
6 μm), a double quantum well active layer 46 of p-AlG
The carrier block layer 47 made of aAs (x = 0.5, t = 0.02 μm), p-AlGaAs (x = 0.2,
t = 0.88 μm), optical waveguide layer 48, p-AlG
A cladding layer 50 made of aAs (Al composition = 0.24, t = 1.1 μm) and a contact layer 51 made of p-GaAs are formed by MOCVD (metal organic chemical vapor deposition) or the like, and furthermore, optical waveguides are formed. N-AlGaAs having a stripe-shaped window in the layer 48 (Al composition ratio x = 0.3
(3, t = 0.1 μm) is buried. Lower surface of substrate 41 and contact layer 5
Electrodes 53 and 52 are respectively formed on the upper surface of 1.

The AlGaAs-based material has a larger bandgap than the InGaAs-based material, and the bandgap tends to increase as the Al composition increases. In this embodiment,
The forbidden band width of the optical waveguide layers 44 and 48 is larger than the forbidden band width of the active layer 46, and the forbidden band width of each of the cladding layers 43 and 50 is larger than that of the optical waveguide layers 44 and 48. Carrier block layers 45, 47 rather than wave layers 44, 48
Each forbidden band is larger.

At the interface of the current blocking layer 49 on the active layer side,
A diffraction grating 61 having a periodic uneven shape is formed, and no diffraction grating exists in the striped window portion 11 where the current blocking layer 49 does not exist, that is, in the current injection region.

Next, the operation will be described. When a positive bias voltage is applied to the electrode 52 of the contact layer 51 and a negative bias voltage is applied to the electrode 53 of the substrate 41, a current flows from the contact layer 51 toward the substrate 41, and a region where the current blocking layer 49 does not exist,
That is, the current density is increased by passing through only the striped window 11.

A current is injected into the active layer 46 as a carrier, and radiates light by carrier recombination. Furthermore, as the amount of injected current is increased, stimulated emission starts, and eventually leads to laser oscillation. The laser light seeps into the optical waveguide layers 44 and 48 on both sides of the active layer 46, and the current blocking layer 49
Also seeps out and is guided. On the other hand, the active layer 46
The carriers inside are confined in the active layer by the presence of the carrier block layers 45 and 47, so that the recombination efficiency is improved.

Here, the period Λ of the diffraction grating 61 is given by the following equation (1).
Is satisfied so that only the wavelength λo selectively oscillates, and as a result, a single mode oscillation is obtained. At this time, in the window 11 which is a current injection region,
Since there is no deterioration in crystallinity, a DFB semiconductor laser having a low oscillation threshold, high efficiency, and long life can be realized.

In this embodiment, the current blocking layer 49 is used.
Although the case where the diffraction grating 61 is formed at the interface on the active layer side has been described, a similar diffraction grating may be formed at the interface on the contact layer side of the current blocking layer 49.

(Fourth Embodiment) FIG. 4 shows a fourth embodiment of the present invention. FIG. 4 (a) is an overall perspective view, and FIG. 4 (b) is a partial perspective view showing the shape of a diffraction grating. This semiconductor laser device is configured as a DFB laser and has n-GaAs
N-GaAs (thickness t =
0.5 μm), n-AlGaAs
s (Al composition ratio x = 0.24, t = 1.1 μm) cladding layer 73, n-AlGaAs (x = 0.2, t
= 0.83 μm), n-AlGa
As (x = 0.5, t = 0.02 μm) carrier block layer 75, undoped InGaAs well layer (I
n composition ratio y = 0.2, t = 0.008 μm) / non-doped AlGaAs barrier layer (Al composition ratio x = 0.2, t =
0.006 μm) double quantum well active layer 76, p
Carrier block layer 77 made of -AlGaAs (x = 0.5, t = 0.02 μm), p-AlGaAs (x = 0.5
0.2, t = 0.83 μm).
-AlGaAs (Al composition = 0.24, t = 1.1 μm)
m), a contact layer 81 made of p-GaAs is formed by MOCVD (metal organic chemical vapor deposition) or the like, and an n- layer having a stripe-shaped window in the optical waveguide layer 78 is formed. A current blocking layer 79 made of AlGaAs (Al composition ratio x = 0.24, t = 0.1 μm) is embedded. Electrodes 83 and 82 are formed on the lower surface of the substrate 71 and the upper surface of the contact layer 81, respectively.

The AlGaAs-based material has a larger forbidden band width than the InGaAs-based material, and the forbidden band width tends to increase as the Al composition increases. In this embodiment,
The forbidden band width of the optical waveguide layers 74 and 78 is larger than the forbidden band width of the active layer 76, and the forbidden band width of each of the cladding layers 73 and 80 is larger than that of the optical waveguide layers 74 and 78. Carrier block layers 75, 77 rather than wave layers 74, 78
Each forbidden band is larger.

In this embodiment, a grating layer 91 having an equivalent function is provided instead of the wavelength control diffraction grating 61 shown in FIG.

The grating layer 91 is formed of p-GaAs (thickness t = 0.05 μm) in the optical waveguide layer 78 so as to form a periodic pattern, and is formed on the active layer side of the current blocking layer 79. It is located between the interface and the active layer 76, is formed to have a uniform thickness in the window portion 11, and is formed in a periodic uneven shape on both sides of the window portion 11, and functions as a diffraction grating having a period Λ. By setting the period Λ to satisfy the expression (1), only the wavelength λo is selectively oscillated, and as a result, a single mode oscillation is obtained. At this time, the window portion 11, which is a current injection region, is protected by the grating layer 91, so that crystallinity is not deteriorated, and a DFB semiconductor laser having a low oscillation threshold, high efficiency, and a long life can be realized.

(Fifth Embodiment) FIG. 5 shows a fifth embodiment of the present invention. FIG. 5 (a) is an overall perspective view, and FIG. 5 (b) is a partial perspective view showing the shape of a diffraction grating. This semiconductor laser device is configured as a DFB laser and has n-GaAs
N-GaAs (thickness t =
0.5 μm), n-AlGaAs
s (Al composition ratio x = 0.24, t = 1.1 μm) cladding layer 73, n-AlGaAs (x = 0.2, t
= 0.83 μm), n-AlGa
As (x = 0.5, t = 0.02 μm) carrier block layer 75, undoped InGaAs well layer (I
n composition ratio y = 0.2, t = 0.008 μm) / non-doped AlGaAs barrier layer (Al composition ratio x = 0.2, t =
0.006 μm) double quantum well active layer 76, p
Carrier block layer 77 made of -AlGaAs (x = 0.5, t = 0.02 μm), p-AlGaAs (x = 0.5
0.2, t = 0.83 μm).
-AlGaAs (Al composition = 0.24, t = 1.1 μm)
m), a contact layer 81 made of p-GaAs is formed by MOCVD (metal organic chemical vapor deposition) or the like, and an n- layer having a stripe-shaped window in the optical waveguide layer 78 is formed. A current blocking layer 79 made of AlGaAs (Al composition ratio x = 0.24, t = 0.1 μm) is embedded. Electrodes 53 and 52 are formed on the lower surface of the substrate 71 and the upper surface of the contact layer 81, respectively.

The AlGaAs-based material has a larger bandgap than the InGaAs-based material, and the bandgap tends to increase as the Al composition increases. In this embodiment,
The forbidden band width of the optical waveguide layers 74 and 78 is larger than the forbidden band width of the active layer 76, and the forbidden band width of each of the cladding layers 73 and 80 is larger than that of the optical waveguide layers 74 and 78. Carrier block layers 75, 77 rather than wave layers 74, 78
Each forbidden band is larger.

In this embodiment, a grating layer 91 having an equivalent function is provided in place of the wavelength control diffraction grating 61 shown in FIG.

The grating layer 91 is formed by forming p-GaAs (thickness t = 0.05 μm) in the optical waveguide layer 78 so as to form a periodic pattern, and is formed on the active layer side of the current blocking layer 79. It is located between the interface and the active layer 76, and is formed in a periodic uneven shape on both sides of the window portion 11, and functions as a diffraction grating with a period Λ. The grating layer 91 is not formed in the window 11. As a method of forming the grating layers on both sides of the window, there is a method utilizing selective growth of the grating layer, or a method of etching and removing the grating layer including the window only by the window.

By setting the period Λ to satisfy the equation (1), only the wavelength λo selectively oscillates,
As a result, a single mode oscillation is obtained. At this time, the window portion 11 serving as the current injection region does not have the grating layer 91, and no layer having a different refractive index exists in the stripe-shaped window portion 11, so that there is an advantage that the mode of the oscillating laser light is not disturbed. .

In the above embodiment, the waveguide layer is made of AlGaAs.
However, in these structures, the waveguide layer is made of InGaP, InGaP.
GaAsP or AlGaAs (Al composition x is 0 ≦ x ≦
A composition containing little or no Al, such as 0.3), is preferable. By setting the waveguide layer to such a composition, the effect of suppressing damage due to oxidation when forming a diffraction grating is further enhanced, and higher reliability can be obtained.

[0055]

As described above, according to the present invention, the periodic structure is formed by forming a diffraction grating for controlling the oscillation wavelength at the interface of the current blocking layer or between the interface and the active layer. Is provided, and only wavelengths satisfying the diffraction condition are selectively oscillated, and stable single mode oscillation is obtained.

Furthermore, since such a diffraction grating is not formed in the current injection region, crystal defects in this region are remarkably reduced. As a result, high oscillation efficiency, high reliability and long life are obtained at a low oscillation threshold. A semiconductor laser device can be realized.

[Brief description of the drawings]

FIGS. 1A and 1B show a first embodiment of the present invention. FIG. 1A is an overall perspective view, and FIG. 1B is a partial perspective view showing a shape of a diffraction grating.

FIG. 2 is a perspective view showing a second embodiment of the present invention.

FIG. 3 is a perspective view showing a third embodiment of the present invention.

4A and 4B show a fourth embodiment of the present invention. FIG. 4A is an overall perspective view, and FIG. 4B is a partial perspective view showing a shape of a diffraction grating.

5A and 5B show a fifth embodiment of the present invention. FIG. 5A is an overall perspective view, and FIG. 5B is a partial perspective view showing a shape of a diffraction grating.

FIG. 6 shows an example of a conventional DFB laser, and FIG.
Is an overall perspective view, and FIG. 6B is a partial perspective view showing the shape of the diffraction grating.

[Explanation of symbols]

 1, 21, 41, 71 Substrate 2, 22, 42, 72 Buffer layer 3, 6, 23, 43, 50, 73, 80 Cladding layer 4, 24, 46, 76 Active layer 5, 26, 49, 79 Current block Layer 7, 28, 51, 81 Contact layer 8, 9, 29, 30, 52, 53, 82, 83 Electrode 10, 31, 61 Diffraction grating 11 Window 25 First cladding layer 27 Second cladding layer 44, 48, 74, 78 Optical waveguide layer 45, 47, 75, 77 Carrier block layer 91 Grating layer

Claims (4)

[Claims] 1. A current block comprising: a pair of cladding layers each having a forbidden band width equal to or greater than a forbidden band width of an active layer on both sides of an active layer; and a stripe-shaped window on at least one of the cladding layers. In a self-aligned semiconductor laser device in which a layer is embedded, an interface for controlling an oscillation wavelength in an area of the current blocking layer or between the interface and the active layer, excluding a stripe-shaped window. A semiconductor laser device comprising a diffraction grating. 2. An optical waveguide layer having a forbidden band width equal to or greater than the forbidden band width of the active layer is provided on one side or both sides of the active layer, and the optical waveguide is sandwiched between the active layer and the optical waveguide layer. A self-aligned semiconductor laser device in which a pair of cladding layers each having a forbidden bandwidth equal to or greater than the forbidden bandwidth of the layer is provided, and a current blocking layer having a stripe-shaped window is embedded in at least one of the cladding layers. A semiconductor laser, wherein a diffraction grating for controlling an oscillation wavelength is formed in an interface of the current blocking layer or between the interface and the active layer and excluding a stripe-shaped window. apparatus. 3. A pair of optical waveguide layers each having a forbidden band width greater than or equal to the forbidden band width of the active layer are provided on both sides of the active layer, and the optical waveguide is sandwiched between the active layer and the optical waveguide layer. A pair of cladding layers each having a forbidden bandwidth equal to or greater than the forbidden bandwidth of the layer are provided, and a forbidden bandwidth equal to or greater than each forbidden bandwidth of the active layer and the optical waveguide layer is provided between the active layer and the optical waveguide layer. A self-aligned semiconductor laser device in which a carrier block layer having: a current blocking layer having a stripe-shaped window is embedded in at least one of the optical waveguide layers; A semiconductor laser device, wherein a diffraction grating for controlling an oscillation wavelength is formed in a region between a layer and a region excluding a stripe-shaped window. 4. The semiconductor material forming the optical waveguide layer is Ga
4. The semiconductor laser device according to claim 2, wherein the semiconductor laser device is made of AlGaAs having an As or Al composition of 0.3 or less, or one of InGaP and InGaAsP.