JP2500588B2 - Semiconductor laser and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure and manufacturing method of a visible light semiconductor laser used as a recording / reading light source for an optical disk memory.

[0002]

2. Description of the Related Art Semiconductor lasers are used as light sources for optical information processing devices, and semiconductor lasers of various structures have been proposed. As an example of a conventional visible light two-beam semiconductor laser, there is one proposed in JP-A-1-243490, which will be described below. This two-beam array semiconductor laser has a sectional structure as shown in FIG. An SiO ₂ insulating film is provided on the n-type GaAs (100) substrate 1 and patterned to form an etching mask for the GaAs substrate 1. Next, the GaAs substrate 1 is etched with a sulfuric acid-based solution to provide a step of 4 to 5 μm in a forward mesa shape having a (111) plane. An n-GaAs buffer layer 2 (thickness 0.5 μm) is formed on the substrate provided with steps.
_{n- (Al x Ga 1-x} ) 0.51 In 0.49 P cladding layer 3
(Thickness 1.5μm, x = 0.5), an undoped (Al _y
Ga _1-y ) _0.51 In _0.49 P active layer 4 (thickness 0.07 μ
m, y = 0), p- (Al x Ga 1-x) 0.51 In 0.49 P
Cladding layer 5 (thickness 1.0 μm, x = 0.5), n−G
The aAs cap layer 6 (thickness 0.2 μm) is sequentially grown by the metal organic chemical vapor deposition method. The growth conditions for the active layer 4 are as follows: growth temperature 700 ° C., source flow rate ratio of group V element and group III element 60
0. Then, using the SiN insulating film as a mask, Zn
Diffusion is performed to form two Zn diffusion stripe regions 7 (depth 0.6 to 0.7 μm, stripe width 4 to 5 μm). Next, the p electrode 8 is vapor deposited, the two stripes are separated, and the n electrode 9 is vapor deposited. The separation distance between stripes is 3
It is considered that 0 to 50 μm is suitable. Thus, the conventional semiconductor laser is obtained. This conventional semiconductor laser has two oscillation wavelengths of about 655 nm and about 685 nm.
Two beams were emitted and the light output was 40 mW.

[0003]

In this conventional two-beam array semiconductor laser, the carrier injection path is formed by Zn.
Since this is done by diffusion, the following problems can be considered. Although there is no description about the carrier concentration of the p-clad layer 5, the carrier concentration of the p-clad layer in the gain waveguide type laser as shown in FIG. 7 is 3 to 5 × 10 ^17.
cm ⁻³ is generally used, and the carrier concentration in the Zn diffusion stripe region 7 is not specifically described, but about 1 × 10 5 is obtained because ohmic contact with the p electrode is obtained.
¹⁹ cm ^-3 is considered necessary.

Due to such high-concentration diffusion into the AlGaInP crystal, among the dopants of the p-clad layer 5 doped by crystal growth, the dopant immediately below the Zn diffusion stripe region 7 becomes an active layer in the direction opposite to the diffusion stripe region 7. The phenomenon of diffusion occurs. Since the active layer has a composition containing less or no Al than the cladding layer, the diffusion rate of the dopant in the active layer is slower in the active layer than in the cladding layer, and the dopant diffused in the active layer piles up in the active layer. The state becomes a high concentration state. As a result, the active layer having an ordered array structure on the (100) plane of the semiconductor laser of the conventional example has a disordered array structure (1
There is a problem in that the wavelength difference between the 11) plane and the semiconductor laser cannot be obtained as originally intended.

Further, the emission intensity of photoluminescence or current injection of a semiconductor crystal having a disordered arrangement structure due to doping or diffusion becomes 1/10 or less as compared with the ordered arrangement structure before the disordered arrangement. The decrease in emission intensity is due to the fact that the dopant and diffusion atoms form non-radiative recombination centers. Therefore, it is difficult to obtain sufficient reliability with a semiconductor laser having an active layer with reduced emission intensity. Another problem is that the semiconductor laser of the conventional example is composed of an ordered array structure and a disordered array structure, so that there is no degree of freedom in combining oscillation wavelengths.

[0006]

In the semiconductor laser of the present invention, a current blocking layer is provided in the formation of a carrier injection path, and in order to increase the degree of freedom in combination of oscillation wavelengths, light emitting regions are formed on mesa slopes having the same or different angles. Is equipped with.

In order to obtain the reliability of the semiconductor laser, the growth temperature of the double hetero structure of the semiconductor laser of the present invention is set to
Ga _0.5 In lattice-matched to GaAs (100) substrate
_The temperature is within the range of ± 10 ° C. at which the band gap energy of the _0.5 P semiconductor crystal becomes minimum.

[0008]

The angle from the (100) plane to the (011) plane is θ
, Ga _0.5 I on the GaAs substrate at each angle of θ
Since the band gap energy when an n _0.5 P semiconductor crystal is grown changes as shown in FIG. 3, a semiconductor laser having an oscillation wavelength according to the angle of the mesa slope can be obtained by providing a light emitting region on the slope of the mesa. .

[0009]

Next, the present invention will be described with reference to the drawings. 1 is a front view of a semiconductor laser according to a first embodiment of the present invention, and FIG. 2 is a sectional view showing its manufacturing process. In manufacturing this semiconductor laser, as shown in FIG. 2A, a resist 13 serving as an etching mask is formed in the [0-11] direction on the n-type GaAs (100) substrate 1 by the photoresist method. Next, as shown in FIG. 2B, the GaAs substrate 1 is etched with an ammonia-hydrogen peroxide-based etchant to remove 45 from the (100) plane.
A step of 5 μm in a forward mesa shape having an angle of degrees is provided.

Subsequently, the first crystal growth is performed at a growth temperature of 650 ° C. by a metal organic chemical vapor deposition (hereinafter MO-VPE) method.
The growth pressure is 75 Torr. This growth temperature is selected such that Ga is lattice-matched to the GaAs (100) substrate.
_This is the temperature at which the band gap energy of _{0.5 In 0.5} P becomes minimum. By this first growth, FIG. 2 (c)
The laminated structure shown in is obtained. The laminated structure is Si-doped n-G
aAs buffer layer 2 (carrier concentration 1 × 10 ¹⁸ cm ⁻³ )
0.3 μm, Si-doped n- (Al _0.6 Ga _0.4 ).
_0.5 In _0.5 P clad layer 3 (carrier concentration 5 × 10 ¹⁷
cm ⁻³ ) of 1 μm, undoped Ga _0.5 In _0.5 P active layer 4 of 0.06 μm, Zn-doped p- (Al _0.6 Ga).
_0.4 ) _0.5 In _0.5 P cladding layer 5 (carrier concentration 3.
5 × 10 ¹⁷ cm ⁻³ ) 0.8 μm, Zn-doped p-Ga
_0.5 In _0.5 P heterobuffer layer 10 (carrier concentration 1
X 10 ¹⁸ cm ^-3 ) 0.8 μm, Si-doped n-GaA
s current blocking layer 11 (carrier concentration 2 × 10 ⁻³ ) 0.7
μm sequentially grown.

Next, as shown in FIG. 2D, the n-GaAs current blocking layer 11 is etched by a photoresist method with a phosphoric acid-based etchant until it reaches the hetero buffer layer 10. Since the etching rate of the Ga _0.5 In _0.5 P heterobuffer layer 10 is extremely slow with respect to the phosphoric acid-based etchant, the heterobuffer layer 10 is in a state where etching is virtually stopped. After removing the resist, the second crystal growth is performed by MO-VPE method at a growth temperature of 650 ° C., a growth pressure of 75 Torr, and a growth rate of 6 μm / h.
Under the above conditions, as shown in FIG.
-GaAs cap layer 12 (carrier concentration 2 × 10 ¹⁹ c
m ⁻³ ) is grown to 3 μm. This second growth rate is p-
In order to reduce the diffusion of Zn from the clad layer 5 to the active layer 4, it is preferable to be as fast as possible. Thereafter, the p-electrode 8 and the n-electrode 9 are formed, and the resist 13 is formed as shown in FIG.
Is provided on the surface of the p electrode 8 and n− is formed by dry etching.
By forming an isolation groove reaching the GaAs current blocking layer 11, the semiconductor laser shown in FIG. 2G of the first embodiment of the present invention is obtained.

Regarding the characteristics of the semiconductor laser of this example, the oscillation wavelength was 656 nm, the oscillation threshold was 85 mA, and the maximum optical output was 20 mW. The semiconductor laser of this embodiment is a gain waveguide type laser. The cavity length at this time is 300 μm.

A second embodiment of the present invention is shown in FIG. 4 and its manufacturing process is shown in FIG. In manufacturing this semiconductor laser, FIGS. 5A and 5B are the same as those in the first embodiment. Subsequently, as shown in FIG. 5C, the hetero buffer layer 10 is grown in the first crystal growth. The growth conditions are the same as in the first embodiment. Next, as shown in FIG. 5D, SiO _{2 serving} as an etching mask and a selective growth mask is formed.
A film is formed on the entire surface of 0.2 μm, and a SiO ₂ film 14 film is formed in stripes on the mesa slope by a photoresist method.
The p-clad layer 5 is 0.25 with a sulfuric acid-based etchant.
Etching is performed to leave μm, and the shape shown in FIG. 5E is obtained.

Subsequently, the second crystal growth was carried out by MO-VPE.
By using the method, the growth temperature is 650 ° C., the growth pressure is 85 Torr, and the growth rate is 3 μm / h.
The current blocking layer 11 (carrier concentration 2 × 10 ¹⁸ cm ⁻³ ) is grown to 0.7 μm to obtain the structure of FIG. And
After removing the SiO ₂ film, the third crystal growth was performed by MO-V.
The PE method was applied, and Zn was deposited on the entire surface as shown in FIG.
Doped p-GaAs cap layer 12 (carrier concentration 2 ×
10 ¹⁹ cm ⁻³ ) is grown to 3 μm. The growth conditions are the same as in the first embodiment. After that, electrodes 8 and 9 are formed, and in order to independently drive the laser on each slope, a separation groove reaching the n-GaAs current blocking layer 11 is formed by dry etching, and the second embodiment of the present invention is performed. A semiconductor laser of FIG. 5 (h) is obtained.

The characteristics of the semiconductor laser of this example were that the oscillation wavelength was 657 nm, the oscillation threshold was 50 mA, and the maximum optical output was 30 mW. The semiconductor laser of this embodiment is a refractive index guided laser. At this time, the cavity length is 3
It is 50 μm.

A third embodiment of the present invention will be described.
FIG. 6 is a cross-sectional view showing a manufacturing process for obtaining mesa slopes having different mesa angles. First, as shown in FIG.
The resist 13 is formed on the GaAs substrate 1 as an etching mask, and the mesa on one side is etched with a phosphoric acid-based etching solution. By this etching, FIG.
A (111) plane is obtained as shown in FIG. Continuing with FIG.
As shown in (c), an etching mask is formed by the resist 13 'to form the other mesa, and a mesa with an angle of 10 degrees is formed with an ammonia-hydrogen peroxide-based etching solution as shown in FIG. 6 (d). To do.

The crystal growth step after the formation of the mesa is performed in the same manner as in the first or second embodiment. As a result, the characteristics of the obtained semiconductor laser are 656 nm on the (111) plane mesa slope and 660 on the mesa slope with an angle of 10 degrees.
An oscillation wavelength of nm was obtained respectively.

Although Ga _0.5 In _0.5 P was used as the active layer in the first to third embodiments, Ga _0.5 In
_0.5 P and (Al _x Ga _1-x ) _0.5 In _0.5 P (0 <x ≤
The multiple quantum well structure according to 1) may be used, and p−
It goes without saying that a multi-quantum barrier structure may be used for the cladding layer. Further, the growth temperature when forming the double hetero structure is ± 10 ° at which the band gap energy of the GaInP crystal lattice-matched with the GaAs substrate becomes minimum.
Within the range of.

[0019]

As described above, according to the present invention, a two-beam semiconductor laser having the same or different oscillation wavelengths can be obtained on the same GaAs substrate. Wavelength selection is Ga _0.5 by setting the mesa angle by etching.
In the case of the In _0.5 P active layer, it is possible to reach 656 nm to 680 nm. Further, in the present invention, since the carrier injection path is formed by the current blocking layer instead of the diffusion stripe, the diffusion of the dopant from the p-clad layer to the active layer is 2
Since it is suppressed to a slight amount that occurs during the crystal growth after the first time, the disordered arrangement of the ordered arrangement structure does not occur. Therefore, the emission intensity does not decrease due to doping or diffusion, and the reliability of the semiconductor laser can be secured. For example, in the semiconductor laser of the first embodiment, no failure occurred until 2000 hours in the constant light output operation test with the case temperature of 50 ° C. and the light output of 5 mW.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor laser according to a first embodiment of the present invention.

2A to 2G are cross-sectional views showing a manufacturing process of the semiconductor laser according to the first embodiment of the present invention.

FIG. 3 is (100) of Ga _0.5 In _0.5 P according to the present invention.
It is a figure which shows the band gap energy when the plane orientation of a GaAs substrate changes from the plane to the (011) plane direction.

FIG. 4 is a sectional view of a semiconductor laser according to a second embodiment of the present invention.

5A to 5H are cross-sectional views showing a manufacturing process of a semiconductor laser according to a second embodiment of the present invention.

FIGS. 6A to 6E are cross-sectional views showing a manufacturing process of a semiconductor laser according to a third embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a conventional semiconductor laser.

[Explanation of symbols]

1 n-GaAs substrate 2 n-GaAs buffer layer _{3 n- (Al 0.6 Ga 0.4)} 0.5 In0.5 P cladding layer 4 of undoped Ga _0.5 In _0.5 P active layer _{5 P- (Al 0.6 Ga 0.4)} 0.5 InP cladding layer 6 n-GaAs cap layer 7 Zn diffusion stripe region 8 p electrode 9 n electrode 10 P-Ga _0.5 In _0.5 P hetero buffer layer 11 n-GaAs current blocking layer 12 P-GaAs cap layer 13, 13 'resist 14 SiO ₂ oxide film

Claims (2)

(57) [Claims] 1. A in the (011) plane direction from the (100) plane
N-type GaAs substrate having a [0-11] direction mesa stripe having a 0 degree (0≤a≤90) plane and a 6 degree (0≤b≤90) plane in the (0-1-1) plane direction. Above (A
l _x Ga _1-x ) _0.5 In _0.5 P semiconductor crystal (0 ≦ x ≦
1) having a double hetero structure in which an n-type clad layer, an active layer serving as a light emitting region, a p-type clad layer, and a heterobuffer layer, which are formed in this order, are sequentially stacked, A semiconductor laser having an n-type current blocking semiconductor layer, wherein laser light is emitted from each of the two active layers of the mesa stripe. 2. A step of forming a mesa stripe on an n-type GaAs substrate, and an n-type clad layer composed of (Al _x Ga _1-x ) _0.5 In _0.5 P crystal on this surface by metalorganic vapor phase epitaxy. A step of sequentially stacking an active layer to be a light emitting region, a p-type clad layer and a heterobuffer layer to form a double heterostructure, and an n-type current blocking layer adjacent to the p-type clad layer or the heterobuffer layer. The step of providing the semiconductor device is characterized in that the growth temperature for forming the double hetero structure is set in a temperature range in the vicinity of which the band gap energy of the GaInP crystal lattice-matched with the GaAs substrate is minimized. Production method.