JP3268958B2 - Semiconductor laser device - Google Patents

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 requires low noise characteristics during reproduction and high output characteristics during recording. When the semiconductor laser device is used in an optical disk system, noise is generated by the return light from the optical disk. In this manner, noise generated when light emitted from the semiconductor laser device is reflected by an external optical system and returns to the semiconductor laser device itself is referred to as return light noise.

It is known to utilize the self-pulsation phenomenon to reduce such return light noise. A self-excited oscillation having a layer having saturable absorption characteristics (hereinafter referred to as a saturable absorption layer) is known. An oscillation type semiconductor laser device has been proposed.

FIG. 9 has a high output characteristic and a low noise characteristic.
1 shows the structure of a conventional AlGaAs semiconductor laser device.
It is a typical sectional view. In FIG. 9, an n-GaAs substrate
1 on Al_0.45Ga_0.55N-cladding 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
The stripe-shaped ridge 41 formed in the center
You.

In the ridge portion 41, p-Al _0.13 Ga
_A p-saturable absorbing layer 50 of _0.87 As is provided. A p-contact layer 6 made of p-GaAs is formed on the ridge portion 41, and an n-contact layer 6 made of n-Al _0.7 Ga _0.3 As is formed on both sides of the ridge portion 41 and on the flat portion 40.
The current block layer 7 is formed.

On the p-contact layer 6 and the n-current block layer 7, a p-cap layer 8 made of p-GaAs is formed. 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 stripe-shaped ridge portion 41. Further, since the effective refractive index under the ridge portion 41 becomes 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, and light is confined in the horizontal direction.

The band gap of the cladding layers 2 and 4 is larger than the band gap of the active layer 3.
The refractive index of the active layer 3 is higher than the refractive indexes of the cladding layers 2 and 4 sandwiching the active layer. Thereby, light is confined in the active layer 4. Vertical confinement of light is performed by such a double heterostructure.

In the semiconductor laser device shown in FIG.
The band gap of the current blocking layer 7 is larger than the band gap of the active layer 3. Thereby, the oscillation light in the active layer 3 is not absorbed by the n-current blocking layer 7.
Therefore, light absorption loss in the n-current blocking layer 7 is small, and high output characteristics can be obtained. On the other hand, the oscillation spectrum of the p-saturable absorption layer 50 provided in the ridge portion 41 causes self-excited oscillation, and the coherence is reduced, so that the return light noise is reduced. Thus, high output characteristics and low noise characteristics are 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 The light generated in 3 is not absorbed by the n-current blocking layer 7. Therefore, compared to a semiconductor laser device that performs refractive index waveguide by absorbing oscillation light in the active layer by the n-current blocking layer, light confinement in the horizontal direction by the refractive index guiding mechanism is weak, and Approaching a semiconductor laser device of the type.

As a result, the transverse mode becomes unstable. For example, when the light output is increased, nonlinearity called kink occurs in the current-light output characteristic, and at the same time, the movement in the emission direction of the laser beam, the output fluctuation, and the like occur. In particular, when the semiconductor laser device is used in an optical disk 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 must be
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 the device 1. This limits the degree of freedom in element design.

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

[0014]

According to a first aspect of the present invention, there is provided a semiconductor laser device formed on a first conductivity type cladding layer.
Formed on the active layer at a flat portion and a central portion on the flat portion
A second conductivity type crack comprising a stripe-shaped ridge portion;
A side surface of the ridge portion and the flat portion.
In a semiconductor laser device with a current blocking layer formed on it
The ridge portion on the flat portion on both sides of the ridge portion.
And a saturable absorbing layer is provided on the side surface of the substrate and in the ridge portion .

A semiconductor laser device according to a second aspect of the present invention.
Is formed on the active layer formed on the first conductivity type cladding layer.
A flat portion and a stripe formed in a central portion on the flat portion
A second conductivity type cladding layer comprising a ridge portion is provided.
Current on the side surface of the ridge portion and the flat portion.
In a semiconductor laser device having a stop layer formed thereon,
On the flat portion on both sides of the ridge portion, on the side surface of the ridge portion and
A saturable absorption layer is provided in the first conductivity type cladding layer.
It was a thing.

Further, the current blocking layer preferably has a band gap of energy larger than the energy of the oscillation light. Further, the saturable absorbing 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 absorbing layers are provided on the regions on both sides of the waveguide.
In particular, in the case of a ridge-embedded semiconductor laser device, a saturable absorption layer is provided on a flat portion on both sides of a ridge portion. Therefore, self-sustained pulsation is obtained by the saturable absorption layer, and oscillation 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 waveguide mechanism is improved, and the transverse mode is stabilized.
In addition, since it is not necessary to reduce the absorption of 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 element design is increased.

Therefore, a semiconductor laser device having a stable transverse mode and a large degree of freedom in design can be obtained while realizing high output characteristics and low noise characteristics. When the current blocking layer has a band gap of energy larger than the energy of the oscillation light, 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 portion 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]

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

In FIG. 1, on an n-GaAs substrate 1,
an n-cladding 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-cladding layer 4 made of p-Al _0.45 Ga _0.55 As are formed in this order. The p-cladding layer 4 includes a flat portion 40 formed on the active layer 3 and a stripe-shaped ridge portion 41 formed at the center of the flat portion 40. On both side surfaces of the ridge portion 41 of the p-cladding layer 4 and on the flat portion 40, p-Al _0.13 Ga _0.87 As
A saturable absorbing layer 5 is formed;

On the ridge portion 41 of the p-cladding 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
A side electrode 9 is formed, and the lower surface of the n-GaAs substrate 1 is
An n-side electrode 10 made of u / Sn / Cr is formed.

It should be noted that a band gap having an energy larger than the energy hν of laser light (h is Planck constant, ν is the frequency of oscillation light) is provided between the flat part 40 and the ridge part 41 of the p-cladding layer 4. May be provided.

Table 1 shows that the n-cladding layer 2, the active layer 3, the p-
The material, refractive index, band gap, and film thickness of the cladding layer 4, the p-saturable absorbing 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.
It is.

[0025]

[Table 1]

Band gap E _{SA of} p-saturable absorption layer 5
Is substantially equal to the band gap E _A (≒ hν) of the active layer 3. The band gap _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 band gap of the n- current blocking layer 7 E _B is larger than the band gap E _A of the active layer 3 (≒ hν).

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 same as those of the active layer 3.
_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 shown in FIG.
Will be described with reference to FIGS. Ma
First, as shown in FIG.
CVD (metal organic chemical vapor deposition) or MBE
N-Al by molecular beam epitaxy_0.45
Ga_0.55N-cladding layer 2 made of As, undoped
Al_0.13Ga _0.87Active layer 3 made of As, p-Al_0.45
Ga_0.55P-cladding layer 4a made of As, p-Al
_0.7Ga_0.3A p-etch stop layer 11 made of As,
p-Al _0.45Ga_0.55P-cladding layer 4 made of As
b and p-contact layer 6 made of p-GaAs.
Continuous growth.

Next, as shown in FIG. 3, after a stripe-shaped SiO ₂ mask (not shown) is formed at the center on the p-contact layer 6, the p-type mask is removed except for the region of the SiO ₂ mask.
Etching the contact layer 6 and the p-cladding layer 4b down to the etching stop layer 11 to form a ridge.
As an etching solution, a mixed solution of an organic carboxylic acid and hydrogen peroxide is used. After that, the SiO ₂ mask is
(Hydrogen fluoride). In FIG. 3, the etching stop layer 11 is removed except for the region of the ridge portion, but the etching stop layer 1 is entirely formed on the p-cladding layer 4a.
1 may remain.

Next, as shown in FIG.
Or on the p-contact layer 6 by the MBE method.
P-cladding layer 4a and p-cladding layer 4a.
Al _0.13Ga_0.87P-saturable absorbing layer 5 made of As and
And n-Al_0.65Ga_0.35N-current block made of As
Layer 7 is formed in order.

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 etchant. Finally, as shown in FIG.
The p-cap layer 8 made of p-GaAs is formed on the p-contact layer 6 and the n-current block layer 7 by the BE method.
Is formed, a p-side electrode 9 made of Au / Cr is formed on the upper surface of the p-cap layer 8, and A-side electrode 9 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 the present embodiment , the p-saturable absorbing 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. To obtain self-excited oscillation, and its p-
The light generated in the active layer 3 is absorbed by the saturable absorbing layer 5. Thereby, the confinement of light in the horizontal direction by the refractive index waveguide 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 element design is increased. Therefore, a semiconductor laser device having a stable transverse mode and a large degree of freedom in design can be obtained while realizing high output characteristics and low noise characteristics.

FIG. 7 shows an AlG according to the first embodiment of the present invention.
It is a typical sectional view showing the structure of an aAs type semiconductor laser device. The semiconductor laser device of FIG. 7 differs from the semiconductor laser device of FIG. 1 in that a p-saturable absorption layer 51 made of p-Al _0.13 Ga _0.87 As is also provided in the ridge portion 41 of the p-cladding layer 4. It is a point. The configuration of other parts is the same as the configuration of the semiconductor laser device of FIG.

In the semiconductor laser device of FIG. 7, the self-sustained pulsation characteristics are further enhanced by the p-saturable absorption layer 51 provided in the ridge portion 41, and the low noise characteristics are further improved. FIG. 8 is a schematic sectional view showing the structure of an AlGaAs semiconductor laser device according to a second embodiment of the present invention.

8 differs from the semiconductor laser device of FIG. 1 in that the n-cladding layer 2 has n-Al
_The point is that an n-saturable absorption layer 52 made of _0.13 Ga _0.87 As is further provided. The configuration of other parts is the same as the configuration of the semiconductor laser device of FIG.

In the semiconductor laser device shown in FIG.
The n-saturable absorption layer 52 provided in the cladding layer 2 further enhances the self-excited oscillation characteristics, and further improves the low noise characteristics.

In the above embodiment, the case where the present invention is applied to a ridge-embedded AlGaAs-based semiconductor laser device has been described. The same can be applied to other semiconductor laser devices.

Although the active layer 3 is 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 of energy larger than the energy of the oscillation light.

[0040]

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

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

When the saturable absorbing layer is provided between the side surface of the ridge portion 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. And the manufacturing time and cost are reduced.

[Brief description of the drawings]

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

FIG. 2 is a first diagram illustrating a method of manufacturing the semiconductor laser device of FIG. 1;
FIG.

FIG. 3 is a second diagram illustrating a method of manufacturing the semiconductor laser device of FIG. 1;
FIG.

FIG. 4 is a third view illustrating a method for manufacturing the semiconductor laser device of FIG. 1;
FIG.

FIG. 5 is a fourth view illustrating the method for manufacturing the semiconductor laser device of FIG. 1;
FIG.

FIG. 6 is a fifth view illustrating the method for manufacturing the semiconductor laser device of FIG. 1;
FIG.

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

FIG. 8 is a schematic sectional view showing the structure of an AlGaAs semiconductor laser device according to a second 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]

 Reference Signs List 1 n-GaAs substrate 2 n-cladding layer 3 active layer 4, 4a, 4b p-cladding layer 5, 51 p-saturable absorbing layer 52 n-saturable absorbing layer 7 n-current blocking layer 40 flat portion 41 ridge portion

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tatsuya Kunisato 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Akira Ibaraki 2-chome, Keihanhondori, Moriguchi-shi, Osaka No. 5 Inside Sanyo Electric Co., Ltd. (56) References JP-A-7-193316 (JP, A) JP-A-61-171186 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 JICST file (JOIS)

Claims (3)

(57) [Claims] A first conductive type clad layer formed on the first conductive type clad layer;
Formed on the active layer at a flat portion and a central portion on the flat portion
A second conductivity type crack comprising a stripe-shaped ridge portion;
A side surface of the ridge portion and the flat portion.
Semiconductor laser device with current blocking layer formed on it
The ridge portion on the flat portion on both sides of the ridge portion.
A saturable absorption layer is provided on the side surface of the semiconductor laser device and in the ridge portion . 2. A second conductive consisting of a stripe-shaped ridge portion formed in a central portion on the flat portion and the flat portion on a first conductivity type formed on the cladding layer <br/> active layer A current blocking layer formed on a side surface of the ridge portion and on the flat portion , wherein the ridge portion is formed on the flat portion on both sides of the ridge portion.
A saturable absorption layer is provided on the side surface of the semiconductor laser device and in the first conductivity type cladding layer . 3. The semiconductor laser device according to claim 1, wherein said current blocking layer has a band gap of energy larger than the energy of oscillation light.