JP2947164B2 - 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, and more particularly to a semiconductor laser device capable of performing high-output stable operation by suppressing deterioration of a cavity facet due to optical damage.

[0002]

2. Description of the Related Art Generally, AlGaAs and AlGaI
In a semiconductor laser device made of an nP-based semiconductor material, the cavity facet is degraded (optical damage, Catastrophic Optical) in accordance with an increase in the optical output.
l Damage (COD) is known to occur. Such optical damage is caused by a rise in the temperature of the end face of the resonator accompanying a high output operation. In other words, the laser light is absorbed at the cavity end face via the surface level,
It generates heat locally. This light absorption increases due to oxidation of the cavity facets and generation of crystal defects. Due to the temperature rise due to the above-mentioned heat generation, the forbidden band width near the end face is reduced, the light absorption is further increased, and the end face temperature is raised. Deterioration occurs.

Conventionally, in order to suppress light absorption at the cavity facet of a semiconductor laser device, various window structures in which a material transparent to laser light is formed on the cavity facet have been tried. For example, in 1989, IEE Journal Quantum Electronics (IEEE J. Quantum Electro)
n. According to the report of Vol. 25, pp. 1495 to 1499, when forming a window structure for suppressing light absorption at the cavity facet, patterning the cavity facet in the active region,
Selective etching and burying regrowth processes are performed.

FIG. 8 shows an example of a process for forming the above-mentioned window structure.

Referring to FIG. 8, a mesa shape 31 is formed on a p-GaAs substrate 30 (FIG. 8A). Then, the first
LPE growth is performed. That is, an n-GaAs layer (block layer) 32 is formed on the p-GaAs substrate 30 (FIG. 8).
(B)). Then, a ridge 33 is formed (FIG. 8C).

After that, a second LPE growth is performed. That is, the cladding layer (p-GaAl
As) 34, a grid layer (p-GaAlAs) 35, an active layer (GaAlAs) 36, a confinement layer (n
-GaAlAs) 37 and a buffer layer (n-GaAl)
As) 38 is formed (FIG. 8D).

Subsequently, after a facet region is formed by etching (FIG. 8E), a cladding layer (n-GaAlAs) 39 and a contact layer (n-GaAs) 40 are sequentially formed by MOCVD growth (FIG. 8).
(F)).

[0008]

As described above, conventionally,
In order to suppress the end face degradation of the semiconductor laser, it is necessary to form a window structure for suppressing light absorption at the end face.
However, forming such a window structure requires the processes of patterning, selective etching, and burying regrowth of the cavity end face in the active region as described above.

In a semiconductor laser using an Al-based material,
Since a strong oxide film is formed at the regrowth interface, the regrowth interface has a window structure with many interface states. Since these interface states increase light absorption, a semiconductor laser using an Al-based material cannot sufficiently suppress COD deterioration. Further, the addition of the window structure as described above causes a problem that the laser element structure becomes extremely complicated and the productivity is significantly reduced due to the yield in each step.

[0010] In addition, the passivation of the dielectric film which is usually used only suppresses the reflectance of the cavity end face and suppresses the promotion of oxidation in the atmosphere. Therefore, if a dielectric film is merely formed on the end face of the resonator as in the prior art, CO 2
It is difficult to improve D deterioration.

An object of the present invention is to provide a laser device which uses a dielectric film to prevent deterioration of a cavity facet and operates stably with high output. That is, according to the present invention, in a semiconductor laser device in which laser light is emitted from a cavity facet, a layer structure of a dielectric film for controlling the reflectance of the cavity facet;
By controlling the film-forming conditions and the film-forming material, the interface level and interface damage are reduced, and a chemically and thermally stable resonator facet is realized, thereby suppressing the deterioration of the facet and providing a high output. And to provide a laser element that operates stably.

[0012]

According to the present invention, there is provided a semiconductor laser device having a pair of cavity facets, wherein at least one of the cavity facets is provided with a first dielectric single-layer film having less interface state or interface damage. Forming a second dielectric single-layer film or a dielectric multilayer film that is chemically and thermally stable. That is, in the present invention, in order to effectively suppress the COD degradation, a dielectric / semiconductor having a small interface state and a small interface damage is formed, and the resonator end face is protected chemically and thermally stably. ing.

[0013]

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

First, referring to FIG.
A method of manufacturing a lateral mode control type semiconductor laser wafer having an As strained quantum well structure and an oscillation wavelength of 0.98 μm band will be described.

The semiconductor laser wafer shown is a normal pressure MOV
Grow by PE equipment. GaAs doped with Si
(001) GaAs: Si buffer layer 2 on substrate 1
(Impurity concentration = 1 × 10 ¹⁸ cm ⁻³ ) 0.5 μm, Al
_0.4 Ga _0.6 As: Si clad layer 3 (impurity concentration = 1
× 10 ¹⁷ cm ⁻³ ) at 2 μm, at a growth temperature of 700 ° C., V /
III Grow at a ratio of 100.

Next, at a growth temperature of 680 ° C., V / II
40 n of Al _0.2 Ga _0.8 As light guide layer 4 with an I ratio of 80
m, GaAs barrier layer 5 is 20 nm, In _0.24 Ga _0.76
The As active layer 6 is 4.5 nm, and the GaAs barrier layer 7 is 5 n.
m, an In _0.24 Ga _0.76 As active layer 8 of 4.5 nm, Ga
An As barrier layer 9 is sequentially grown to a thickness of 20 nm.

Subsequently, the Al _0.2 Ga _0.8 As light guiding layer 10 is 40 nm, and the Al _0.4 Ga _0.6 As: Mg cladding layer 11 (impurity concentration = 1 × 10 ¹⁸ cm ⁻³ ) is 1.5 μm.
m, GaAs: Mg cap layer 12 (impurity concentration = 1 ×
10 ¹⁹ cm ⁻³ ) is grown by 1 μm in vapor phase.

Next, referring to FIGS. 2 and 3, a process for processing the above-described semiconductor laser wafer into a transverse mode control type laser will be described. FIG. 2 shows (−110) of the semiconductor laser wafer after the formation of the mesa stripe in the [−110] direction.
FIG.

First, SiO ₂ is formed on the uppermost GaAs cap layer 12 of the semiconductor laser wafer shown in FIG.
[-11] shown in FIG.
0], an SiO ₂ stripe 13 having a width of 4 μm is formed. Using the SiO ₂ stripe 13 as a mask, etching is performed by a selective etching technique until the Al _0.4 Ga _0.6 As: Mg clad layer 11 has a depth of 0.3 μm to form a mesa stripe shown in FIG.

Subsequently, as shown in FIG. 3, a side portion of the mesa stripe is formed on a 0.8 μm-thick Al _{0.6 layer} by a selective growth technique using the SiO ₂ stripe as a mask.
Ga _0.4 As: Si current blocking layer 14 (impurity concentration =
1 × 10 ¹⁸ cm ⁻³ ) and 0.8 μm-thick GaAs: S
i-current blocking layer 15 (impurity concentration = 1 × 10 ¹⁸ c
Embedding growth is performed sequentially at m ⁻³ ).

Further, after removing the SiO ₂ mask, a 1 μm-thick GaAs: Mg cap layer 16 (impurity concentration = 1 × 10 ¹⁹ cm ⁻³ ) is grown to obtain a lateral mode control type semiconductor laser wafer.

Contact electrodes are vapor-deposited on both sides of the laser wafer, and then perpendicular to the laser stripe [1].
The laser bar is obtained by cleavage along the direction [10] so that the cavity length becomes 700 μm.

Next, a description will be given of a passivation method for reducing the interface state or interface damage on the resonator end face and realizing a chemically and thermally stable end face.

Here, a multipolar sputtering apparatus was used for depositing the dielectric film. As shown in FIG. 4, in the 0.98 μm-band strained quantum well laser bar 17 made of the above-described semiconductor material, first, a 30 nm-thick Si is used as a first dielectric layer.
The N _x films 18 and 19 are deposited on the end face of the resonator at a deposition temperature of 150 ° C. and a sputter power density of 4 W / cm ⁻² .
The SiN _x film is reactive with the III -V compound semiconductor because it is a material of non-oxide is low. Therefore, an interface with few levels can be obtained. In addition, surface damage can be reduced by optimizing film forming conditions.

Next, as shown in FIG. 5, oxidation of the SiN _x film and contamination of impurities in the atmosphere are suppressed.
In order to form an end face that is chemically and thermally stable and to control the reflectance of the end face of the resonator, the first dielectric film SiN _x
On the film, an Al ₂ O ₃ single-layer film 20 as a second dielectric film and A
A multilayer film of the l ₂ O ₃ film 21 and the amorphous Si film 22 was deposited to have an end face reflectance of 3% on the front surface and 95% on the back surface. At this time, the Al ₂ O ₃ film 21 and the amorphous Si film 22 were formed at a film formation temperature of 240 ° C., and the sputter power densities were 8.5 and 6 W / cm ⁻² , respectively.

Here, the Al ₂ O ₃ film 21 is more damaged during film formation than the first dielectric films SiN _x films 18 and 19, but has higher chemical and thermal stability than the SiN _x film. Is excellent. Therefore, it can be effectively used as the second dielectric layer.

The material of the first dielectric single-layer film formed directly on the cavity facet can be variously selected depending on the structure, material configuration, and operating light output of the laser element. As the dielectric film material used as the first dielectric single-layer film, the above-mentioned Si is used.
In addition to N _x , there are, for example, SiC and Ge.

After the passivation step is completed, the laser bar is cleaved into individual laser elements and fused to a heat sink to complete the semiconductor laser element. In the above-described example, the description has been given of the 0.98 μm band semiconductor laser. However, not only the 0.98 μm band semiconductor laser but also semiconductor lasers of other wavelength bands (0.6 to 0.8 μm) are used.
m-band semiconductor laser).

In the above example, the first dielectric single-layer film and the second dielectric film in contact with the first dielectric film are made of different materials. By letting By using the same material for the first and second dielectric layers, the end face degradation life can be improved.

Hereinafter, an example of a semiconductor laser device using the same material for the first and second dielectric layers will be described. In addition,
As the semiconductor laser wafer used in this example, the same one as the semiconductor laser wafer described in FIG. 1 was used.

First, the lateral mode control type semiconductor laser wafer on which the contact electrodes are formed is cleaved in the [110] direction perpendicular to the laser stripe so that the cavity length becomes 700 μm, and the laser bar 23 is obtained.

As shown in FIG. 6, a 30 nm-thick Al film serving as a first dielectric film is
_{The 2} O ₃ films 24 and 25 are formed at a film forming temperature of 180 ° C. and a sputter power density of 3.5 W / cm ⁻² . At this time, by lowering the sputtering power at the time of film formation, scattering collision of high energy particles is reduced, and interface damage at the time of film formation is reduced. However, a chemically and thermally stable film cannot be obtained due to a decrease in the density of the dielectric film.

[0033] Subsequently, as shown in FIG. 7, a single layer of Al ₂ 0 ₃ film 26 which is a second dielectric film layer and the Al ₂ 0 ₃ film 27
And an amorphous Si film 28, thereby controlling the end face reflectance to 3% on the front surface and 95% on the back surface. At this time, the Al ₂ O ₃ film 27 and the amorphous Si film 2
8 means that the film was formed at a film formation temperature of 240 ° C., and the sputter power densities were 8.5 and 4 W / cm ⁻² , respectively.

By increasing the sputtering power density of the Al ₂ O ₃ film 27 as the second dielectric film, the damage during the film formation is increased, but the density of the film is also increased. Therefore, a dielectric film that is chemically and thermally stable can be obtained.

As film forming parameters (parameters of film forming conditions) that can change the characteristics of the dielectric film, for example, film forming material, film forming temperature, sputtering power,
r pressure, distance between target and sample.

Finally, the semiconductor laser device is completed by cleaving the laser bar into individual laser devices and fusing it to a heat sink.

As described above, by changing the film forming conditions of the same dielectric film, the material which can improve the deterioration of the end face is not limited to the Al ₂ O ₃ film, but may be, for example, SiN _x , Si
This is also possible for each material of C, Ge, or Si.

In the above-described example, the semiconductor laser of the 0.98 μm band has been described. However, not only the semiconductor laser of the 0.98 μm band but also semiconductor lasers of other wavelength bands (0.
6-0.8 μm band semiconductor laser).

The above-described steps do not involve complicated processes as in the conventional window structure formation, and require only approximately the same number of steps as in the conventional dielectric film passivation. Therefore, productivity does not decrease. Further, it has wide applicability in various semiconductor laser devices.

[0040]

As described above, according to the present invention, the first
Since the film forming material or the film forming conditions of the dielectric layer and the second dielectric layer are changed, an interface with less interface damage and interface level is formed, and chemically and thermally stable resonance is achieved. There is an effect that a container end face can be realized. Since the reduction of the interface state and the interface damage reduces the light absorption at the cavity end face, it is extremely effective in suppressing the COD deterioration. Furthermore, by covering the resonator end face with a chemically and thermally stable layer, there is an effect that long-term reliability can be obtained by suppressing the contamination of impurities and the successive deterioration of the end face.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a layer structure of a semiconductor laser wafer.

FIG. 2 is a cross-sectional view when a semiconductor laser wafer is selectively etched by an SiO ₂ stripe.

FIG. 3 is a cross-sectional view when embedded regrowth is performed on a selectively etched semiconductor laser wafer.

FIG. 4 is a cross-sectional view illustrating an example of coating a semiconductor laser bar with a first dielectric film.

FIG. 5 is a diagram for explaining an example of coating a semiconductor laser bar with a second dielectric film.

FIG. 6 is a diagram illustrating another example of coating a semiconductor laser bar with a first dielectric film.

FIG. 7 is a diagram illustrating another example of coating a semiconductor laser bar with a second dielectric film.

FIG. 8 is a view for explaining a conventional method for manufacturing a semiconductor laser device.

[Explanation of symbols]

1 GaAs substrate 2 GaAs: Si buffer layer 3 Al _0.4 Ga _0.6 As: Si cladding layer 4 Al _0.2 Ga _0.8 As optical guide layer 5 GaAs barrier layer 6 In _0.24 Ga _0.76 As active layer 7 GaAs barrier layer 8 In _0.24 Ga _0.76 As Active layer 9 GaAs barrier layer 10 Al _0.2 Ga _0.8 As optical guide layer 11 Al _0.4 Ga _0.6 As: Mg clad layer 12 GaAs: Mg cap layer 13 SiO ₂ stripe 14 Al _0.6 Ga _0.4 As: Si current block layer 15 GaAs: Si Current block layer 16 GaAs: Mg cap layer 17,23 Semiconductor laser bar 18,19 SiN _x film 20,21,24,25,26,27 Al ₂ O ₃ film 22,28 Amorphous Si film

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/18

Claims (3)

(57) [Claims] 1. A semiconductor laser device having a pair of cavity facets, a first dielectric single-layer film formed on at least one cavity facet and having a small interface state or interface damage, and the first dielectric material It is formed on a single layer film and a chemically and thermally stable second dielectric layer, the first dielectric single
The layer film is SiN _x , and the second dielectric film is Al ₂ O
_3. A semiconductor laser device, which is ₃ . 2. A semiconductor laser device according to claim 1, the semiconductor laser element, wherein the second dielectric film is a single layer film. In the semiconductor laser element according to 3. The method of claim 1, the semiconductor laser element, wherein the second dielectric film is a multilayer film.