JPH10125995A - Semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a mesa stripe-buried semiconductor laser to be lessened in threshold value and improved in kink level. SOLUTION: When an outer clad layer 6 which controls a lateral mode is formed by etching, etching is controlled in depth by an etching stop layer 5. The etching stop layer 5 is formed of a multi-quantum well layer, the well layer is formed so thick as to have a band gap which does not absorb light oscillated in an active layer 3, and etching can be surely stopped by the well layers. The barrier layer of the etching stop layer 5 is set lower in refractive index than the clad layer, and the average refractive index of all the etching stop layer 5 is set lower than those of the clad layers 4 and 6, whereby light distribution is restrained from spreading wide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device that oscillates in a single transverse mode.

[0002]

2. Description of the Related Art Recently, an AlGaInP-based semiconductor laser oscillating in the red region has been put into practical use in response to a demand for an increase in the capacity of an optical disk device, and the performance thereof has been urgently improved. As a structure of this semiconductor laser, a structure as shown in FIG. 4 has been reported (see Japanese Patent Application Laid-Open No. 6-244497).

The semiconductor laser device shown in FIG. 4 has a p-type (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P inner cladding layer 16, an etching stop layer 17,
Mold (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P Outer clad layer 1
Then, the outer clad layer 18 is etched to the etching stop layer 17 while leaving a part of the outer clad layer 18 in a mesa shape, and the n-type GaAs block layer 8 is regrown in the etched portion to form an optical waveguide structure. In this case, only the mesa-shaped portion of the current is injected.

In the structure shown in FIG. 4, an etching stop layer 17 is formed in order to produce a structure by etching with good reproducibility.
Has a multiple quantum well structure, and in any of the plurality of well layers, the etching is reliably stopped, and the band gap energy of the layer that stops the etching is set to be larger than the oscillation energy of the active layer. Absorption of the semiconductor laser is prevented, and characteristics such as the oscillation threshold of the semiconductor laser are prevented from deteriorating.

Japanese Patent Application Laid-Open No. 3-240287 discloses an AlGaAs having a single etching stop layer.
A system-based semiconductor laser is disclosed. In this semiconductor laser, it has been pointed out that the refractive index of the etching stop layer is larger than that of the surrounding cladding layer, the light distribution is widened in this portion, the light output is reduced, and the occurrence of kink is a problem.
As a solution to this, there has been proposed a method of doping the etching stop layer at a high concentration to lower the refractive index.

[0006]

However, the conventional semiconductor laser device shown in FIG. 4 has a problem that the performance of the semiconductor laser, such as the threshold value, light output, and kink level, cannot be improved to a certain extent. Was.

[0007] The reason is that the etching stop layer is G
It is formed of an aInP well layer and an (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P barrier layer. As shown in FIG. 5, the light distribution is distributed by the etching stop layer, and the light distribution can be freely designed. Because it cannot be done.

Further, in the technique disclosed in Japanese Patent Application Laid-Open No. 3-240287, it is difficult to apply high-concentration doping of the etching stop layer to FIG. 4 in order to solve the first problem. was there.

[0009] The reason is that doping a multiple quantum well layer with a dopant at a high concentration has an adverse effect such that the multiple quantum well structure is destroyed due to internal diffusion, and the emission efficiency is reduced due to the diffusion of the dopant. Because.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to make it possible to freely design the light distribution while maintaining the etching stop function and the light non-absorbing function of the multiple quantum well etching stop layer. An object of the present invention is to provide a semiconductor laser device that realizes a reduction in the value and an increase in output.

[0011]

In order to achieve the above object, a semiconductor laser device according to the present invention has a first
A conductive type cladding layer and an etching stop layer composed of a multiple quantum well layer, a mesa-type first conductive type cladding layer on the etching stop layer, and a second mesa-type cladding layer laterally sandwiching the cladding layer. A semiconductor laser device comprising a conductive or insulating current blocking layer, wherein the bandgap energy of the multiple quantum well layer is larger than the emission energy of the active layer, and the average of the multiple quantum well layer is The refractive index is equal to or smaller than the refractive indexes of the two cladding layers.

The refractive index of the well layer of the multiple quantum well is larger than the refractive indexes of the two cladding layers, and
The refractive index of the barrier layer of the multiple quantum well is smaller than the refractive indexes of the two cladding layers.

[0013]

As shown in FIG. 2, the structure of the etching stop layer of the semiconductor laser device according to the present invention comprises a well portion having a larger refractive index than the surrounding cladding layer and a barrier portion having a smaller refractive index. Since the ratio is equal to or smaller than that of the cladding layer, light is not guided, and optically, the etching stop layer can be regarded as a uniform cladding layer, thereby enabling device design.

The effect of reliably stopping etching by a plurality of well layers and the effect of non-absorbing light by expanding the band gap by forming a quantum well are the same as those in the related art.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a sectional view showing a semiconductor laser device according to Embodiment 1 of the present invention.

As shown in FIG. 1, an n-type GaAs substrate 1
(Si-doped, n = 2 × 10 ¹⁸ cm ⁻³ ) on the n-type (A
1 _0.6 Ga _0.4 ) _0.51 In _0.49 P cladding layer 2 (n = 1 ×
10 ¹⁸ cm ⁻³ , thickness 1.2 μm) and the MQW active layer 3
(Undoped, oscillation wavelength 685 nm) and p-type (Al
_0.6 Ga _0.4 ) _0.51 In _0.49 P inner cladding layer 4 (p =
5 × 10 ¹⁷ cm ⁻³ , thickness 0.3 μm), an etching stop layer 5 (well layer: GaInP40Å, two layers, barrier layer: AlInP100Å, three layers), and p-type (Al _0.6 G
a _0.4 ) _0.51 In _0.49 P outer cladding layer 6 (p = 5 ×
10 ¹⁷ cm ⁻³ , thickness 1 μm) and p-type Ga _0.51 In _0.49
The P cap layer 7 is sequentially grown and formed.

For the crystal growth, a metal organic vapor phase epitaxy (MOVPE) under reduced pressure is used. The growth conditions are a temperature of 700 ° C., a pressure of 70 Torr, V / III = 150, and a total flow rate of a carrier gas (H ₂ ) of 15 l / l. min. The raw materials include trimethyl indium (TMI: (CH ₃ ) ₃ In), triethyl gallium (TEG: (C ₂ H ₅ ) ₃ Ga, trimethyl aluminum (TMA: (CH ₃ ) ₃ Al, arsine (A
sH ₃ ), phosphine (PH ₃ ), P-type dopant: dimethyl zinc (DMZ: (CH ₃ ) ₂ ), and n-type dopant: disilane (Si ₂ H ₆ ).

A stripe-shaped SiO ₂ mask is formed on the wafer grown through the above steps by photolithography.

Next, using a SiO ₂ mask, the p-type Ga _0.51 In _0.49 P cap layer 7 is first etched in a stripe shape with a bromine-based etchant.
_0.6 Ga _0.4 ) _0.51 In _0.49 Hydrogen bromide-based etchant with an etching rate of 3000 ° / min for P, an etching rate for AlInP of 1 μm / min, and an etching rate for GaInP of 50 ° / min, p-type (Al _0.6 Ga _0.4 ) _{The 0.51} In _0.49 P outer clad layer 6 was etched. At this time, the etching for 1 min or more is stopped at the etching stop layer 5 with respect to the etching time of 5 mm (the state in which the GaInP is slowly etched), and a mesa stripe of the same size can be reliably formed with good reproducibility. there were.

Next, with the SiO ₂ mask attached, the MO
A second growth is performed by VPE to form an n-type GaAs block layer 8. Then, the SiO ₂ is removed and the MOV
A third growth is performed by PE to form a p-type GaAs contact layer 9.

After the n-type electrode 11 and the p-type electrode 10 are formed on the wafer prepared as described above by vacuum evaporation and sputtering, the cavity is cleaved to a length of 600 μm, and 10% of the front surface and 90% of the rear surface are formed. A dielectric reflection film is formed by sputtering.

The semiconductor laser manufactured according to the present invention described above was compared with a conventional semiconductor laser. In the comparative semiconductor laser, the barrier layer of the etching stop layer of the above-described embodiment was (Al _0.6 Ga _0.4 ) _0.51 In _0.49 P, and the other dimensions, doping concentrations, and structures were all the same as those of the second embodiment. And By preparing three wafers of each of these two types and arbitrarily extracting 50 pellets from each wafer and comparing the average value of the threshold values of 150 pellets, it is 42 mA in the conventional structure, whereas it is 36 mA in the present embodiment. And the threshold was lowered.

This is because, by the operation of the present invention, light is not distributed to the etching stop layer in one direction, and
This is because light loss due to the block layer of the type GaAs is reduced.

(Embodiment 2) FIG. 3 is a sectional view showing Embodiment 2 of the present invention. The structure and the manufacturing method are basically the same as those of the first embodiment, except that the outer side of the mesa-shaped stripe is n in order to make the waveguide mode of light real waveguide.
The type is changed to the Al _0.51 In _0.49 P block layer 13.

Accordingly, the n-type cladding layer is formed with (Al _0.7
Ga _{0.3) 0.51} In _0.49 to P19, p-type inner cladding layer _{(Al 0.7 Ga 0.3) 0.51 In} 0.49 P12, the p-type outer cladding layer _{(Al 0.4 Ga 0.6) 0.51 In} 0.49 P14
Changed to Also in the second embodiment, in order to verify the effect of the present invention, a laser beam in which only the guide layer of the etching stop layer 5 is made of (Al _0.6 Ga _0.4 ) _0.51 In _0.49 P is prepared, and the laser characteristics are compared. did. Comparing the average values of 150 semiconductor lasers extracted from three wafers in the same manner as in the first embodiment, the threshold value of the laser having the etching stop layer of the conventional structure was 35 mA, and the kink generation light output was 55 mW. On the other hand, in the laser of the second embodiment, the threshold value was 29 mA and the kink generation light output was 65 mW, and both characteristics were improved.

In the embodiment described above, the crystal system is A
Although described as the 1GaInP system, the AlGaAs system, etc.
The present invention is applicable to other crystalline semiconductor laser devices. In the above-described embodiment, the composition, film thickness, doping concentration, cavity length, end face reflectivity and the like of the active layer and the cladding layer are described with specific values.
It is needless to say that the value is not limited to the above value, and the designer determines the value for the required laser characteristic.

[0028]

As described above, according to the present invention, the characteristics of the semiconductor laser device can be improved, such as the reduction of the oscillation threshold value and the improvement of the kink generation light output. The reason is that light is no longer guided to the etching stop layer.

[Brief description of the drawings]

FIG. 1 is a sectional view showing Embodiment 1 of the present invention.

FIG. 2 is a schematic diagram showing light distribution for explaining the operation of the present invention.

FIG. 3 is a sectional view showing Embodiment 2 of the present invention.

FIG. 4 is a sectional view showing a conventional semiconductor laser device.

FIG. 5 is a schematic diagram showing a light distribution of a conventional semiconductor laser device.

[Explanation of symbols]

_{Reference Signs List} 1 n-type GaAs substrate 2 n-type (Al _0.6 Ga _0.4 ) _0.51 In _0.49 P cladding layer 3 MQW active layer 4 p-type (Al _0.6 Ga _0.4 ) _0.51 In _0.49 P inner cladding layer 5 etching stop layer 6 p-type (Al _0.6 Ga _0.4 ) _0.51 In _0.49 P outer cladding layer 7 p-type Ga _0.51 In _0.49 P cap layer 8 n-type GaAs block layer 9 p-type GaAs contact layer 10 p-type electrode 11 n-type electrode 12 p-type (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P inner cladding layer 13 n-type Al _0.51 In _0.49 P blocking layer 14 p-type (Al _0.4 Ga _0.6 ) _0.51 In _0.49 P outer cladding layer 15 n-type (Al _0.5 Ga _0.5 ) _0.51 In _0.49 P cladding layer 16 p-type (Al _0.5 Ga _0.5 ) _0.51 In _0.49 P inner cladding layer 17 etching stop layer 18 p-type (Al _0.5 Ga _0.5 ) _0.51 In _0.49 P layer Uta clad layer 19 n-type (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P clad layer

Claims (2)

[Claims] A first conductivity type cladding layer on the active layer;
An etching stop layer comprising a multiple quantum well layer, a mesa-type first conductivity type cladding layer on the etching stop layer, and a second conductivity type or insulation type cladding layer laterally sandwiching the cladding layer. A current blocking layer, wherein the bandgap energy of the multiple quantum well layer is greater than the emission energy of the active layer, and the average refractive index of the multiple quantum well layer is A semiconductor laser device having a refractive index equal to or smaller than a refractive index of a cladding layer. 2. The refractive index of the well layer of the multiple quantum well is:
2. The semiconductor according to claim 1, wherein the refractive index of the barrier layer of the multiple quantum well is larger than the refractive index of the two clad layers and smaller than the refractive index of the two clad layers. 3. Laser device.