JPH04309281A - Semiconductor laser and its manufacture - Google Patents

Abstract

PURPOSE:To provide an easily usable semiconductor laser by improving the characteristics, such as vertical radiation angle, characteristic temperature, etc., of an A GaInP photoconductive laser. CONSTITUTION:The refractive index distribution of this semiconductor laser is made asymmetrical by making the band gap of an n-clad layer 2 in a double hetero-structure smaller than that of a p-type clad layer 4 in the structure. In addition, the growing temperature of the double hetero-structure is set higher than the temperature at which the band gap of GaInP becomes the minimum in the growing temperature dependency of the band gap of the GaInP.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a barcode reader,
Regarding semiconductor lasers used as light sources for optical discs, etc.
In particular, the present invention relates to a visible light semiconductor laser with an oscillation wavelength of 680 nm or less.

0002

2. Description of the Related Art Semiconductor lasers are used as light sources for optical information processing devices, and semiconductor lasers with various structures have been proposed.

An example of a conventional visible laser is reported in IEICE study group material OQE88-10, P65.

The structure of the above conventional example is shown in FIG. This semiconductor laser has n-(Al) on an n-GaAs substrate (1).
YGa1-Y)0.5In0.5P cladding layer (
2), Undoped Ga0.5 In0.5 P active layer (
3), P-(AlYGa1-Y)0.5 In0.
5 P cladding layer (4) and n-GaAs current blocking layer (6) are sequentially laminated to form an n-GaAs current blocking layer (6).
), a p-GaAs contact layer (8) is laminated thereon, and electrodes (9) and (10) are formed to obtain a semiconductor laser.

In the conventional example, the cladding layer composition y=0.7,
At a cavity length of 300 μm, the characteristics are as shown in Table 1 below.

[0006]

[0007]

[Problems to be Solved by the Invention] In general, semiconductor lasers are required to have a low oscillation threshold current in order to reduce power consumption, and in order to increase light utilization efficiency, the ratio of the vertical radiation angle to the horizontal radiation angle is set to 1. That is, the closer the beam is to a circular beam, the better the kink level of the optical output is to widen the usable optical output range, and the higher the maximum CW oscillation temperature is to give more leeway to the heat dissipation design.

In this conventional semiconductor laser, in order to reduce the oscillation threshold current, the active layer thickness and the p-cladding layer thickness are optimized to obtain an oscillation threshold current of 65 to 70 mA. However, as shown in Table 1, with respect to the active layer thickness, the vertical radiation angle
Since the kink level and the maximum CW oscillation temperature change, the characteristics of conventional semiconductor lasers have a problem in that they do not have characteristics that are easy to use in practice.

[0009]

[Means for Solving the Problems] The semiconductor laser of the present invention is used for the cladding layer because the vertical radiation angle, kink level, and maximum CW oscillation temperature are related to the double heterostructure formed around the active layer. Focusing on the physical properties of AlGaInP type crystal, we changed the band gap of the n-cladding layer to the p-
By making the bandgap smaller than that of the cladding layer and creating an asymmetric refractive index difference, the vertical radiation angle and kink level are the same as the active layer thickness of 0.06 μm, and the maximum CW oscillation temperature is the same as that of the active layer. A semiconductor laser having the same level of characteristics as a 0.1 μm thick semiconductor laser can be obtained.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a cross-sectional view of a laser according to an embodiment of the present invention. First, the first crystal growth is performed by metal organic vapor phase epitaxy (MO-VPE) at a growth pressure of 76 Torr and a growth temperature of 660°C. Through this first vapor phase growth, n-Ga
An n-GaAs intermediate layer (
12) with a thickness of 0.3 μm and a carrier concentration of 1×1018c.
m-3,n-(Al0.58Ga0.42)0.5 I
The n0.5P cladding layer (2) has a thickness of 1.0 μm, the carrier concentration is 6×1017 cm-3, and the undoped Ga0.5In0.5P active layer (3), which will become the light emitting region, has a thickness of 0.
．． 07 μm, p-(Al0.6 Ga0.4)0.5
In0.5 P cladding layer (4) with a thickness of 0.8 μm,
Carrier concentration 3 to 5 x 1017 cm-3, p-Ga0.
5 In0.5 P or p-Al0.6 Ga0.4
The As buffer layer (5) has a thickness of 0.1 μm and a carrier concentration of 1×1018 cm−3, and the n-GaAs current block layer (6) has a thickness of 0.6 μm and a carrier concentration of 3×1018 cm.
Stack m-3 sequentially. The dopants include Zn for p-type,
The n-type uses Si.

Next, [0-11
] A striped groove (7) is formed reaching the p-buffer layer (5) in the direction. The width of this groove is determined by the p-buffer layer (
5) side is 7 μm.

[0012] Next, the second crystal growth was performed using MO-VPE.
By the method, the growth temperature is 650℃ at normal growth pressure.
The p-GaAs contact layer (8) was formed to a thickness of 4 μm.
Grow to a carrier concentration of 2 x 1019 cm-3. Thereafter, electrodes (9) and (10) are formed to construct a semiconductor laser according to the present invention.

The growth temperature for the first crystal growth condition is shown in FIG.
In the growth temperature dependence of the bandgap of GaInP that is lattice matched to the GaAs substrate shown in FIG. Such a change in band gap is due to the regularity of the arrangement of Ga and In.

Under the crystal growth conditions according to the present invention (Al
The band gap of the YGa1-Y)0.5In0.5P crystal is y=0.5 to 0.6 for the Al composition y.
In the range of , it changes by about 5 meV per y=0.01. Moreover, the p-cladding layer does not depend on the p-type dopant,
Depending on the amount of doping, the arrangement state of group III atoms in the crystal changes, causing a change in the band gap. In AlGaInP-based crystals, the higher the doping, the larger the band gap. For this reason, p in this example
-The band gap difference between the cladding layer and the n-cladding layer is
It is about 30 meV.

[0015]

Effects of the Invention The characteristics of the semiconductor laser having the structure of the embodiment described above are as follows: active layer thickness 0.07 μm, cavity length 300 μm, oscillation threshold current 70 mA, vertical radiation angle 34°, kink level 9. ~10mW, maximum CW temperature 95
°C was obtained.

The improvement of the vertical radiation angle is achieved by combining the p-cladding layer and the n-cladding layer.
- An asymmetric waveguide is constructed due to the difference in band gap between the cladding layers, that is, the difference in refractive index. Since there is a difference in refractive index between the cladding layers, more laser light leaks into the n-cladding layer than the p-cladding layer and is guided. As a result, the near field of the laser beam at the output end face spreads in the vertical direction, so that the vertical radiation angle becomes small, and as shown in FIG. 3, it is reduced by about 6 degrees to 34 degrees compared to the conventional example.

The improvement in kink level can be explained as follows. Since the laser of the present invention is a gain waveguide semiconductor laser, the optical waveguide centered around the stripe portion is maintained by a phenomenon called spatial hole burning, but the lateral refractive index difference caused by this is As the power increases, the transverse refractive index difference decreases due to the plasma effect, causing transverse mode distortion, that is, kink. If the optical density of the active layer is reduced in order to maintain the transverse mode, it becomes possible to increase the kink-generated optical output. Therefore, since the semiconductor laser of the present invention is a gain waveguide type, the lateral refractive index difference can be controlled by controlling the spread of the injection current by changing the width of the groove (7) that serves as the current injection window, but the oscillation This is difficult because the influence on the threshold value is large, and it is advisable to reduce optical confinement in the vertical direction. For this reason, the refractive index difference of the cladding layer (
The kink level can be improved by making the bandgap asymmetrical, and as a result of experiments, the trend shown in FIG. 4 was obtained, and the kink level could be improved to 10 mW with a band gap difference of 25 to 30 meV in the cladding layer.

As for the reliability of the semiconductor laser of the present invention, an estimated lifetime of more than 20,000 hours has been obtained when energized at a constant light output of 5 mW at 50°C.

The above characteristics are the characteristics of GaIn shown in FIG.
As a growth temperature based on the growth temperature dependence of the P bandgap, although it can be obtained at 620°C or higher,
At temperatures below ℃, satisfactory results were not obtained. This is thought to be related to the regularity of the arrangement of group III atoms Al, Ga, and In and the dopant Zn.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a semiconductor laser of the present invention.

FIG. 2 is a diagram showing the growth temperature dependence of the bandgap of GaInP.

FIG. 3 is a diagram showing the dependence of the vertical radiation angle on the active layer thickness.

FIG. 4 is a diagram showing the relationship between the band gap difference between the p-cladding layer and the n-cladding layer and the kink level.

FIG. 5 is a cross-sectional view of a conventional semiconductor laser.

[Explanation of symbols]

1 n-GaAs substrate 12 n-GaAs intermediate layer 2 n-(AlYGa1-Y)0.5 In
0.5 P cladding layer (0.5≦y≦1) 3 Undoped Ga0.5 In0.5 P active layer 4 p-(AlYGa1-Y)0.5 I
n0.5 P cladding layer 5 p-Ga0.5 In0.5 P or p-A
lZ Ga1-Z As buffer layer (0.4≦z≦1) 6 n-GaAs current blocking layer 7 groove 8 p-GaAs contact layer 9, 10 electrode

Claims (2)

[Claims] Claim 1: On a GaAs substrate, a light emitting region (
AlX Ga1-X )0.5 In0.5 P(0≦
x≦0.2) The active layer is made of two (AlYGa1-Y
)0.5 In0.5 P (0.5≦y≦1) It has a double heterostructure sandwiched between cladding layers, and adjacent to the cladding layer, Ga0.5 having the same conductivity as the cladding layer
In0.5 P or AlZ Ga1-Z As (0.
4≦z≦1) comprising a buffer layer, and adjacent to the buffer layer, comprising a GaAs layer having a conductivity opposite to that of the buffer layer,
In the two cladding layers of the semiconductor laser, which has a straight groove in the GaAs layer and an adjacent GaAs contact layer having the same conductivity as the buffer layer, the band gap of the n-type cladding layer is changed to that of the p-type cladding layer. A semiconductor laser characterized by having a bandgap smaller than the band gap of the layer by 20 meV or more. 2. On a GaAs substrate, (AlX Ga1
-X)0.5In0.5P (0≦x≦0.2) The active layer is formed by two (AlYGa1-Y)0.5I layers with a larger band gap and different conductivity from each other.
n0.5 P (0.5≦y≦1) Double heterostructure sandwiched between cladding layers, Ga0.5 In0.5 P or A
The lZ Ga1-Z As (0.4≦z≦1) buffer layer and GaAs current blocking layer are formed by metal-organic vapor phase epitaxy, so that the band gap that depends on the growth temperature of GaInP, which is lattice-matched to the GaAs substrate, becomes minimum. a step of sequentially laminating the layers at a growth temperature higher than the GaAs current blocking layer; a step of forming a groove in the GaAs current blocking layer; and a step of filling the groove to form the GaAs current block layer.
s A method for manufacturing a semiconductor laser, comprising at least the steps of forming a GaAs contact layer on the current blocking layer, and forming electrodes on the GaAs contact layer and the GaAs substrate, respectively.