JPH08316563A - Semiconductor laser device - Google Patents

Abstract

PURPOSE: To provide a semiconductor laser device which is high in output, low in noise, stable in a lateral mode, and large in degree of freedom of design. CONSTITUTION: A P-saturable absorption layer 5 possessed of a band gap nearly equal to that of an active layer 3 is formed on the flat 40 of a P-type clad layer 4 and the side face of a ridge 41. An N-current block layer 7 possessed of a larger energy band gap than the energy of oscillation light is formed.

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 having high output characteristics and low noise characteristics.

[0002]

2. Description of the Related Art A semiconductor laser device used as a light source for an optical disk system is required to have a low noise characteristic during reproduction and a high output characteristic during recording. When the semiconductor laser device is used in an optical disc system, noise is generated by the returning light from the optical disc. The noise generated when the light emitted from the semiconductor laser device is reflected by the external optical system and returns to the semiconductor laser device itself is called return optical noise.

It is known to use a self-excited oscillation phenomenon to reduce such return light noise, and a self-excited layer including a layer having saturable absorption characteristics (hereinafter referred to as saturable absorption layer) is known. Oscillation type semiconductor laser devices have been proposed.

FIG. 9 has a high output characteristic and a low noise characteristic.
The structure of a conventional AlGaAs semiconductor laser device is shown.
It is a schematic sectional view. In FIG. 9, an n-GaAs substrate
Al on 1_0.45Ga_0.55N-clad layer made of As
2, undoped Al_0.13Ga_0.87Active layer made of As
3 and Al _0.45Ga_0.55P-cladding layer made of As
4 are formed in order. The p-clad layer 4 is an active layer
3 and the flat portion 40 formed on the flat portion 40
It consists of a striped ridge 41 formed in the center.
It

In the ridge portion 41, p-Al _0.13 Ga is contained.
_A p-saturable absorber layer 50 of _0.87 As is provided. The upper ridge portion 41 composed of p-GaAs p-contact layer 6 is formed, on both sides and flat portions 40 of the ridge portion 41 is composed of n-Al _0.7 Ga _0.3 As n-
The current blocking layer 7 is formed.

A p-cap layer 8 made of p-GaAs is formed on the p-contact layer 6 and the n-current blocking layer 7. A p-side electrode 9 is formed on the upper surface of the p-cap layer 8, and an n-side electrode 10 is formed on the lower surface of the n-GaAs substrate 1.

In this semiconductor laser device, the current supplied from the p-side electrode 9 is blocked by the n-current blocking layer 7 and injected only into the striped ridge portion 41. Further, since the effective refractive index under the ridge portion 41 is larger than the effective refractive index under the flat portion 40 excluding the region of the ridge portion 41, the refractive index waveguide is formed in the region under the ridge portion 41. An optical waveguide is formed by the mechanism to confine light in the horizontal direction.

Further, the band gaps of the cladding layers 2 and 4 are larger than the band gap of the active layer 3,
The refractive index of the active layer 3 is higher than the refractive indices of the cladding layers 2 and 4 that sandwich the active layer 3. Thereby, the light is confined in the active layer 4. Such double hetero structure confine light in the vertical direction.

In the semiconductor laser device of FIG. 9, n-
The band gap of the current blocking layer 7 is larger than that of the active layer 3. As a result, the oscillation light in the active layer 3 is not absorbed by the n-current blocking layer 7.
Therefore, the absorption loss of light in the n-current blocking layer 7 is small, and high output characteristics can be obtained. On the other hand, the p-saturable absorption layer 50 provided in the ridge portion 41 causes the self-oscillation of the oscillation spectrum, and the coherence is reduced, so that the return optical noise is reduced. In this way, high output characteristics and low noise characteristics can be obtained.

[0010]

As described above, in the conventional semiconductor laser device of FIG. 9, since the band gap of the n-current blocking layer 7 is large in order to obtain high output characteristics, the active layer is not formed. The light generated in 3 is not absorbed by the n-current blocking layer 7. Therefore, as compared with a semiconductor laser device that performs index guiding by absorbing oscillation light in the active layer by the n-current blocking layer, light confinement in the horizontal direction by the index guiding mechanism is weak, and gain guiding is performed. Type semiconductor laser device.

As a result, the transverse mode becomes unstable. For example, when the optical output is increased, the current-optical output characteristic has a non-linear characteristic called kink, and at the same time, the laser beam moves in the emitting direction and the output fluctuates. In particular, when the semiconductor laser device is used in an optical disc system, the transverse mode is required to be stable.

In order to suppress the instability of the transverse mode as much as possible, the light generated in the active layer 3 is applied to the ridge portion 4.
The distance between the active layer 3 and the p-saturable absorption layer 50 must be set large so as to reduce the amount absorbed by the p-saturable absorption layer 50 in FIG. This limits the freedom of design of the device.

An object of the present invention is to provide a semiconductor laser device having a stable transverse mode and a large degree of freedom in design while realizing high output characteristics and low noise characteristics.

[0014]

A semiconductor laser device according to the present invention is a semiconductor laser device in which a waveguide is formed in an active layer, in which saturable absorption layers are provided on regions on both sides of the waveguide. is there.

In particular, a clad layer having a flat portion and a striped ridge portion formed in the central portion on the flat portion is provided on the active layer, and a current blocking layer is provided on the side surface and the flat portion of the ridge portion. In the case of the formed semiconductor laser device, it is preferable that saturable absorption layers are provided on the flat portions on both sides of the ridge portion.

Further, it is preferable that the current blocking layer has a band gap having an energy larger than that of the oscillation light. Furthermore, the saturable absorption layer may be provided between the side surface of the ridge portion and the upper surface of the flat portion and the current blocking layer.

[0017]

In the semiconductor laser device according to the present invention, saturable absorption layers are provided on both sides of the waveguide.
Particularly, in the case of a ridge-embedded semiconductor laser device, a saturable absorption layer is provided on the flat portions on both sides of the ridge portion. Therefore, self-excited oscillation is obtained by the saturable absorption layer, and the oscillated light in the active layer is absorbed by the saturable absorption layer. Thereby, the confinement of light in the horizontal direction by the refractive index guiding mechanism is improved, and the transverse mode is stabilized.
Further, since it is not necessary to reduce the absorption of the oscillation light by the saturable absorption layer, it is not necessary to set a large distance between the saturable absorption layer and the active layer, and the degree of freedom in designing the device is increased.

Therefore, it is possible to obtain a semiconductor laser device having a stable lateral mode and a large degree of freedom in designing, while realizing high output characteristics and low noise characteristics. When the current blocking layer has a bandgap with an energy larger than that of the oscillated light, the light absorption loss in the current blocking layer is reduced, so that higher output characteristics can be obtained.

When the saturable absorbing layer is provided between the side surface of the ridge and the upper surface of the flat portion and the current blocking layer, the saturable absorbing layer and the current blocking layer are formed in a continuous process. can do.

[0020]

EXAMPLE FIG. 1 shows AlGa according to a first example of the present invention.
FIG. 3 is a schematic cross-sectional view showing the structure of an As semiconductor laser device.

In FIG. 1, on an n-GaAs substrate 1,
an n-clad layer 2 made of n-Al _0.45 Ga _0.55 As,
An active layer 3 made of undoped Al _0.13 Ga _0.87 As and a p-clad layer 4 made of p-Al _0.45 Ga _0.55 As are sequentially formed. The p-cladding layer 4 is composed of a flat portion 40 formed on the active layer 3 and a striped ridge portion 41 formed in the center of the flat portion 40. On the both side surfaces of the ridge portion 41 of the p-cladding layer 4 and on the flat portion 40, p made of p-Al _0.13 Ga _0.87 As is formed.
-The saturable absorber layer 5 is formed.

On the ridge portion 41 of the p-clad layer 4,
A p-contact layer 6 made of p-GaAs is formed,
On the p-saturable absorption layer 5, n-Al _0.65 Ga _0.35 As
The n-current blocking layer 7 is formed. p-
On the contact layer 6 and the n-current blocking layer 7,
A p-cap layer 8 made of p-GaAs is formed. On the upper surface of the p-cap layer 8, p made of Au / Cr is formed.
The side electrode 9 is formed, and A is formed on the lower surface of the n-GaAs substrate 1.
An n-side electrode 10 made of u / Sn / Cr is formed.

A band gap having an energy larger than the energy hν of laser light (h is Planck's constant, ν is the frequency of oscillation light) is provided between the flat portion 40 and the ridge portion 41 of the p-cladding layer 4. An etching stopper layer having the above may be provided.

Table 1 shows the n-cladding layer 2, the active layer 3 and the p-layer.
The materials, refractive index, band gap and film thickness of the cladding layer 4, the p-saturable absorption layer 5 and the n-current blocking layer 7 are shown. The width W of the lower surface of the ridge portion 41 is, for example, 3 μm.
Is.

[0025]

[Table 1]

Band gap E _{SA of} p-saturable absorption layer 5
Is approximately equal to the bandgap E _A (≈hν) of the active layer 3. Band gap of the n-cladding layer 2 _Enc and p-
The band gap E _pc of the cladding layer 4 is larger than the band gap E _A (≈hν) of the active layer 3. The bandgap E _B of the n-current blocking layer 7 is larger than the bandgap E _A (≈hν) of the active layer 3.

Further, the refractive index N _nc of the n-cladding layer 2 and the refractive index N _pc of the p-cladding layer 4 are the refractive index N of the active layer 3.
Smaller than _A , and the refractive index N of the n-current blocking layer 7
Greater than _B.

Next, a method of manufacturing the semiconductor laser device of FIG.
Will be described with reference to process sectional views of FIGS. Well
First, as shown in FIG. 2, on the n-GaAs substrate 1, MO
CVD method (metalorganic chemical vapor deposition method) or MBE method
N-Al by (molecular beam epitaxial growth method)_0.45
Ga_0.55N-clad layer 2 of As, undoped
Al_0.13Ga _0.87Active layer 3 made of As, p-Al_0.45
Ga_0.55P-clad layer 4a made of As, p-Al
_0.7Ga_0.3A p-etch stop layer 11 of As,
p-Al _0.45Ga_0.55P-clad layer 4 made of As
b and the p-contact layer 6 made of p-GaAs
Grow continuously.

Next, as shown in FIG. 3, a stripe-shaped SiO ₂ mask (not shown) is formed on the central portion of the p-contact layer 6, and then p is removed except for the SiO ₂ mask region.
-The contact layer 6 and the p-clad layer 4b are etched down to the etching stop layer 11 to form a ridge portion.
As the etching liquid, a mixed liquid of organic carboxylic acid and hydrogen peroxide is used. After that, the SiO ₂ mask is HF
Remove with (hydrogen fluoride). In FIG. 3, the etching stopper layer 11 is removed except for the region of the ridge portion, but the etching stopper layer 1 is entirely formed on the p-clad layer 4a.
1 may remain.

Next, as shown in FIG.
On the p-contact layer 6 by the MBE method or the MBE method.
P- on the side surface of the pad layer 4b and on the p-clad layer 4a.
Al _0.13Ga_0.87P-saturable absorption layer 5 composed of As and
And n-Al_0.65Ga_0.35N-current block consisting of As
Layer 7 is formed in sequence.

Further, as shown in FIG. 5, the n-current blocking layer 7 and the p-saturable absorption layer 5 on the p-contact layer 6 are etched using a phosphoric acid-based etching solution. Finally, as shown in FIG. 6, MOCVD method or M
The p-cap layer 8 made of p-GaAs is formed on the p-contact layer 6 and the n-current blocking layer 7 by the BE method.
, A p-side electrode 9 made of Au / Cr is formed on the upper surface of the p-cap layer 8, and A is formed on the lower surface of the n-GaAs substrate 1.
An n-side electrode 10 made of u / Sn / Cr is formed.

In the semiconductor laser device of this embodiment, since the p-saturable absorption layer 5 is provided on the flat portion 40 of the p-cladding layer 4 and on the side surface of the ridge portion 41, the p-saturable absorption layer 5 is formed. Self-excited oscillation is obtained by the
The saturable absorption layer 5 absorbs the light generated in the active layer 3. Thereby, the confinement of light in the horizontal direction by the refractive index guiding mechanism is improved, and the transverse mode is stabilized.

Further, since it is not required to set a large distance between the p-saturable absorption layer 5 and the active layer 3, the degree of freedom in designing the device increases. Therefore, it is possible to obtain a semiconductor laser device having a stable lateral mode and a large degree of freedom of design while realizing high output characteristics and low noise characteristics.

FIG. 7 shows AlG according to the second embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view showing the structure of an aAs semiconductor laser device. The semiconductor laser device of FIG. 7 is different from the semiconductor laser device of FIG. 1 in that the ridge portion 41 of the p-cladding layer 4 is also provided with a p-saturable absorption layer 51 of p-Al _0.13 Ga _0.87 As. That is the point. The configuration of the other parts is similar to that of the semiconductor laser device of FIG.

In the semiconductor laser device of FIG. 7, the p-saturable absorption layer 51 provided in the ridge portion 41 further enhances the self-oscillation characteristic and further improves the low noise characteristic. FIG. 8 is a schematic sectional view showing the structure of an AlGaAs semiconductor laser device according to the third embodiment of the present invention.

The semiconductor laser device shown in FIG. 8 is different from the semiconductor laser device shown in FIG. 1 in that n-Al in the n-clad layer 2 is different.
_The point is that the n-saturable absorption layer 52 made of _0.13 Ga _0.87 As is further provided. The configuration of the other parts is similar to that of the semiconductor laser device of FIG.

In the semiconductor laser device of FIG. 8, n-
The n-saturable absorption layer 52 provided in the cladding layer 2 further enhances the self-sustained pulsation characteristic and further improves the low noise characteristic.

In the above embodiments, the case where the present invention is applied to the ridge-buried type AlGaAs semiconductor laser device is explained. However, the present invention is an AlGaInP semiconductor laser device having high output characteristics and low noise characteristics. It can be similarly applied to other semiconductor laser devices.

Although the active layer 3 is composed of a single layer in the above embodiment, an active layer having a quantum well structure may be used. Also in this case, it is preferable that the current blocking layer has a band gap having an energy larger than that of the oscillation light.

[0040]

As described above, according to the present invention, since the saturable absorbing layers are provided on the regions on both sides of the waveguide, the saturable absorbing layer can provide self-sustained pulsation and the refractive index guide. Good confinement of light in the horizontal direction by the wave mechanism.
Further, it is not required to set a large distance between the saturable absorption layer and the active layer. Therefore, it is possible to obtain a semiconductor laser device having a stable lateral mode and a large degree of freedom of design while realizing high output characteristics and low noise characteristics.

In particular, when the current blocking layer has a bandgap with an energy larger than that of the oscillation light, the light absorption loss in the current blocking layer is reduced, and higher output characteristics can be obtained.

Further, when the saturable absorbing layer is provided between the side surface of the ridge and the upper surface of the flat portion and the current blocking layer, the saturable absorbing layer and the current blocking layer are formed in a continuous process. It is possible to reduce the manufacturing time and the manufacturing cost.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing the structure of an AlGaAs semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a first diagram showing a method of manufacturing the semiconductor laser device of FIG.
FIG.

FIG. 3 is a second view showing a method of manufacturing the semiconductor laser device of FIG.
FIG.

4 shows a third method for manufacturing the semiconductor laser device of FIG.
FIG.

5 is a fourth diagram showing a method of manufacturing the semiconductor laser device of FIG.
FIG.

6 is a fifth view showing a method of manufacturing the semiconductor laser device of FIG.
FIG.

FIG. 7 is a schematic sectional view showing the structure of an AlGaAs semiconductor laser device according to a second embodiment of the present invention.

FIG. 8 is a schematic sectional view showing a structure of an AlGaAs semiconductor laser device according to a third embodiment of the present invention.

FIG. 9 is a schematic cross-sectional view showing the structure of a conventional AlGaAs semiconductor laser device.

[Explanation of symbols]

 1 n-GaAs substrate 2 n-clad layer 3 active layer 4,4a, 4b p-clad layer 5,51 p-saturable absorption layer 52 n-saturable absorption layer 7 n-current block layer 40 flat part 41 ridge part

Front page continuation (72) Inventor Tatsuya Kunizato 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Akira Ibaraki 2-5-5 Keihan-hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. A semiconductor laser device having a waveguide formed in an active layer, wherein a saturable absorption layer is provided on regions on both sides of the waveguide. 2. A clad layer comprising a flat portion and a striped ridge portion formed in the central portion on the flat portion is provided on the active layer, and a current blocking is provided on a side surface of the ridge portion and on the flat portion. A semiconductor laser device in which a layer is formed, wherein a saturable absorption layer is provided on the flat portions on both sides of the ridge portion. 3. The semiconductor laser device according to claim 1, wherein the current blocking layer has a band gap having an energy larger than that of the oscillation light. 4. The semiconductor laser device according to claim 2, wherein the saturable absorption layer is provided between a side surface of the ridge portion and an upper surface of the flat portion and the current blocking layer. .