JPH04266079A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To achieve a small vertical spread angle thetav which is equal to or less than 20 deg. with a high light entrapment coefficient GAMMAv in a semiconductor laser device. CONSTITUTION:Low refractive index layers 13 and 17 are provided at one portion of a region where a distance from an activation layer 15 is shorter than an oscillation wavelength within each region of a first clad layer 12 and a second clad layer 18.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device that can be used as a light source for various information processing, communications, and measurements using laser light.

0002

2. Description of the Related Art In recent years, the demand for semiconductor laser devices as light sources for optical disk devices and optical communication devices has rapidly increased. In order to meet this demand, semiconductor laser devices having various structures have been researched and developed and put into practical use.

One of the problems when putting semiconductor laser devices into practical use is that the divergence angle of the laser light emitted from the semiconductor laser device is much larger than that of gas lasers or solid-state lasers, and the aspect ratio is much larger than 1. The problem is that the optical system for this becomes complicated.

[0004] By controlling the stripe width, the beam divergence angle in the direction parallel to the double heterojunction surface forming the active region (hereinafter referred to as horizontal divergence angle) can be increased to 10
The beam divergence angle in the direction perpendicular to the double heterojunction surface (hereinafter referred to as
This is because it is difficult to reduce the vertical divergence angle (referred to as the vertical divergence angle) to about 20° or less in the case of a semiconductor laser device having a conventional structure.

The vertical divergence angle in a semiconductor laser device having a conventional structure will be explained below with reference to the drawings.

FIG. 6 is a cross-sectional view of a semiconductor laser device having a conventional structure, and FIG. 7 is a diagram showing the refractive index distribution in the vicinity of the active layer. In FIG. 5, 1 is a semiconductor substrate, 2 is a first cladding layer, 3 is an active layer, 4 is a second cladding layer, and 5 is a cap layer.

The vertical divergence angle θv for the optical waveguide shown in FIG. 6 can be approximately expressed by the following equation.

[0008] θv≒4・(n22−n12)・d/λ0) (
rad) Here, n1 and n2 are the refractive indices of the cladding layers 2, 4 and the active layer 3, respectively, d is the thickness of the active layer 3,
λ0 is the wavelength in vacuum.

From this equation, in order to reduce the vertical divergence angle θv in a semiconductor laser device with an oscillation wavelength λ0, it is necessary to reduce the thickness d of the active layer 3, or to reduce the thickness d of the cladding layer 2,
What is necessary is to increase the refractive index n1 of the active layer 3 and decrease the value of (n22-n12) (the refractive index n2 of the active layer 3 is almost uniquely determined from the oscillation wavelength λ0 and cannot be changed).

However, when the vertical divergence angle θv is reduced by the above method, the degree of confinement of light in the active layer 3 is reduced, resulting in a problem that the threshold current density for oscillation is increased.

The light confinement coefficient Γv in the active layer 3 can be approximately expressed by the following equation for this structure.

Γv≒2π2・(n22−n12)・(d/λ0)2
FIG. 8 shows the vertical divergence angle θv when the thickness d of the active layer 3 and the Al composition x1 of the cladding layers 2 and 4 (therefore, the refractive index n1 of the cladding layer) are changed in an AlGaAs-based semiconductor laser device with λ0 = 830 nm. It shows the change in the light confinement coefficient Γv.

As is clear from FIG. 8, the thickness d of the active layer 3
, the value of Γv when θv<20° is achieved no matter which of the refractive indices n1 of the cladding layers 2 and 4 is changed is θv>30.
The value of Γv decreases to less than a fraction of the value when realizing .degree., and the threshold current density increases significantly.

[0014]

As described above, in the above structure, even if the thickness d of the active layer 3 and the cladding layers 2 and 4
Even if a small vertical divergence angle θv can be achieved by changing the refractive index n1 of
As the current density decreases, the threshold current density increases significantly,
There was a practical problem.

In view of the above drawbacks, it is an object of the present invention to provide a semiconductor laser device that can easily realize a small vertical divergence angle θv of 20° or less while having a high light confinement coefficient Γv. .

[0016]

[Means for Solving the Problems] In order to achieve the above object, a semiconductor laser device according to the present invention has a part of the cladding layer close to the active layer having a refractive index lower than that of the cladding layer other than that part. Depends on configuration.

[0017]

[Operation] According to this structure, the light distribution near the active layer changes as follows by introducing the semiconductor layer having a small refractive index.

That is, since the light intensity in this low refractive index layer portion is suppressed, the optical power corresponding to the decrease is distributed over both sides of the low refractive index layer, that is, on the active layer side and the cladding layer side. At this time, the extra optical power distributed on the active layer side increases the optical confinement coefficient Γv in the active layer, while the extra optical power distributed on the cladding layer side widens the near-field distribution, thereby significantly reducing the vertical divergence angle θv. can be done.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of a semiconductor laser device according to an embodiment of the present invention, and FIG. 2 is a diagram showing the refractive index distribution in the vicinity of the active layer.

In FIG. 1, 11 is n-GaAs (10
0), 12 is a 2 μm thick n-Al
a first cladding layer made of 0.5Ga0.5As, 13
is a low refractive index layer made of n-Al0.6Ga0.4As with a thickness of 0.3 μm; 14 is a layer with a thickness of 0.075 μm made of the same components as the first cladding layer 12; and 15 is a layer with a thickness of 0.0 μm.
Active layer made of 5 μm and rope Al0.06Ga0.94As, 16 is p-Al0 with a thickness of 0.075 μm.
．． A layer made of the same component as the second cladding made of 5Ga0.5As, 17 is p-Al0.6G with a thickness of 0.3 μm.
A low refractive index layer made of a0.4As, 18 a second cladding layer made of p-Al0.5Ga0.5As with a thickness of 2 μm, and 19 a cap layer made of p-GaAs with a thickness of 3 μm.

According to this configuration, the vertical divergence angle θv obtained by calculation is 13.2°, and the light confinement coefficient Γ
v is 0.139. On the other hand, low refractive index layers 13 and 17
In the case of a semiconductor laser device with a conventional structure that does not have θv
Since Γv=30.2° and Γv=0.141, it follows that θv can be significantly reduced without almost decreasing Γv.

In fact, the vertical divergence angle θv of a broad area type semiconductor laser device with a stripe width of 20 μm, which was prototyped by crystal growth using the MOCVD method based on this example, was 12.8° as shown in FIG. The threshold current density at this time was 1530 A/cm2, and the semiconductor laser device had a conventional structure without a low refractive index layer (θv=30.5°
A value almost equal to the threshold current density of 1450 A/cm2 was obtained.

In addition, in the refractive index guided semiconductor laser device with a stripe width of 2 μm manufactured based on this example, the horizontal divergence angle θh is 13.0°, and the aspect ratio of the far-field pattern ( A semiconductor laser device with an ellipticity of approximately 1 could be realized.

In the above embodiment, a structure having a specific film thickness and composition was described, but by changing the film thickness and composition, the optical confinement coefficient Γv and the vertical divergence angle θv can be changed quite freely. can be selected.

FIG. 5 shows the low refractive index layer 13 in the structure of FIG.
, 17 film thickness d1, active layer 15 and low refractive index layers 13, 17
This figure shows the values of the optical confinement coefficient Γv and the vertical divergence angle θv when the distance d2 between the two is changed. As is clear from this figure, by appropriately selecting the film thickness and position of the low refractive index layers 13 and 17, it is possible to simultaneously achieve both a high optical confinement coefficient and a small vertical divergence angle, which could not be achieved with semiconductor laser devices of conventional structure. It can be achieved.

The above-mentioned effect is due to the suppression of the light distribution intensity where the low refractive index layers 13 and 17 exist. Therefore, when the low refractive index layers 13 and 17 are introduced into a region where the light distribution intensity is large in the absence of the low refractive index layers 13 and 17, that is, a region where the distance from the active layer 15 is within the wavelength, as described above, The effect will be noticeable.

Note that in this embodiment, the low refractive index layers 13, 1
Although No. 7 describes the case where the mixed crystal ratio of each material of the first and second cladding layers 12 and 18 is changed, it is also possible to change the materials themselves.

Although this embodiment has been described with reference to an AlGaAs semiconductor laser device, similar effects can be obtained with semiconductor laser devices other than this type.

Further, in this embodiment, the crystal growth was performed by MOCVD, but it goes without saying that the effects of the present invention can also be achieved by other crystal growth methods.

[0031]

As described above, in the present invention, the refractive index of at least a portion of each region of the first and second cladding layers whose distance from the active layer is smaller than the oscillation wavelength is lower than that of the cladding other than this portion. Since the refractive index is smaller than the refractive index of the layer, it is possible to provide a semiconductor laser device in which the vertical divergence angle can be made extremely small without reducing the light confinement coefficient.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a semiconductor laser device according to an embodiment of the present invention.

[Figure 2] Refractive index distribution diagram near the active layer of the same semiconductor laser device

[Fig. 3] A diagram showing the relationship between the vertical spread angle θv and the light intensity when the stripe width is 20 μm in the same semiconductor laser device.

[Figure 4
] Diagram showing the relationship between vertical divergence angle θv and light intensity and far-field pattern when the stripe width is 2 μm in the same semiconductor laser device.

FIG. 5 is a diagram showing changes in the optical confinement coefficient Γv and vertical divergence angle θv when the film thickness d1 of the low refractive index layer and the distance d2 between the active layer and the low refractive index layer of the same semiconductor laser device are changed.

[
Figure 6: Cross-sectional view of a conventional semiconductor laser device

[Figure 7] Refractive index distribution diagram near the active layer of the same semiconductor laser device

FIG. 8: Thickness d of the active layer and Al composition x1 of the cladding layer (that is, refractive index n1 of the cladding layer) of the same semiconductor laser device.
A diagram showing the relationship between the vertical spread angle θv and the light confinement coefficient Γv, with θv as a parameter.

[Explanation of symbols]

11 Semiconductor substrate 12 First cladding layer 13 Low refractive index layer 14 Layer 15 made of the same component as the first cladding layer
Active layer 16 Layer 17 made of the same components as the second cladding layer
Low refractive index layer 18 Second cladding layer 19 Cap layer

Claims (3)

[Claims] 1. A first cladding layer of the same conductivity type as the semiconductor substrate, an active layer, and a second cladding layer of the opposite conductivity type to the first cladding layer, which are sequentially formed on a semiconductor substrate of one conductivity type. In the semiconductor laser device, the distance from the active layer is shorter than the oscillation wavelength, and the cladding layer has a refractive index in a portion of each region of the first and second cladding layers other than this portion. A semiconductor laser device characterized in that the refractive index is smaller than the refractive index of the semiconductor laser device. 2. The semiconductor laser device according to claim 1, wherein a part of the cladding layer having a low refractive index has a mixed crystal ratio of a material of the cladding layer other than that region. 3. The semiconductor laser device according to claim 1, wherein a part of the cladding layer having a small refractive index is made of a material different from the material of the cladding layer other than that region.