JPH05152676A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To lower the oscillation threshold value in the title refractive index waveguide type lateral mode controlled AlGaInP base semiconductor laser using a natural superlattice. CONSTITUTION:The title semiconductor laser is provided with the double hetero structure wherein the first conductivity type clad layer 2, an active layer 3 formed of a natural super lattice comprising GaInP or AlGaInP and the second conductivity type clad layer 4 successively laminated while the region beside stripe different from the region inside the stripe out of the active layer 3 containing impurity atoms has larger band gap energy than that of the stripe inside. In such a construction, the face orientation of the first conductivity type GaAs substrate 1 is inclined in the face orientation exceeding 0 deg. and not exceeding 10' in the direction from (001) to (-110) or (1-10). Furthermore, the energy difference and the refractive index difference between the inside and the side of stripe of the active layer 3 can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a low threshold AlGaInP
System semiconductor laser.

[0002]

2. Description of the Related Art Recently, an AlGaInP semiconductor laser is formed by a metal organic chemical vapor deposition method (hereinafter abbreviated as MOVPE method), and a long-life visible light semiconductor laser has been realized (Gomei et al., Electronic Letters, Vol. 23). (19
87) Page 85: A. Gomyo et al. E
electronics Letters Vol. Two
3, (1987), pp. 85). The MOVPE method is trimethylaluminum (TMAI), triethylgallium (TEGa), trimethylindium (TMIn).
Is a vapor-phase growth method using an organic metal vapor such as and a hydride gas such as phosphine (PH ₃ ) as a raw material.
The growth of lGaInP depends on TMAI, TEGa, TM
Epitaxial growth is performed by introducing and heating In vapor and PH ₃ gas on the GaAs substrate. In most cases, the plane orientation of a GaAs substrate is a plane without (001) tilt or a plane tilted by 2 ° in the [110] direction from (001). Recently, in order to shorten the wavelength, a plane orientation inclined from the (001) direction to the (110) direction may be used.

In applying this semiconductor laser to a bar code reader, an optical disk reader, etc., it is desirable to perform single transverse mode oscillation with a low threshold current value. Therefore, the conventional AlGaInP-based semiconductor laser has an n-type A-type on a (001) -n-type GaAs substrate 11 as shown in FIG.
clad layer 2 made of 1GaInP and AlGaInP
Alternatively, the active layer 3 made of GaInP, p-type AlGaIn
A thick clad layer 4 made of P was formed in a mesa stripe shape, and an n-type GaAs current confinement layer 11 was provided on a portion other than the upper portion of the mesa of this layer [eg, Fujii et al., Electronics Letters, Vol. 23 (1987)]. 938 page; FUJII et al. ELECTRONON
ICS LETTERS 23 (1987) 938]. The distance between the n-type current confinement layer 11 and the active layer 3 is 0.3 μm, and the n-type GaAs current confinement layer 11 functions as a light absorption layer, resulting in single transverse mode oscillation.

[0004]

However, the conventional A
The 1GaInP-based semiconductor laser has a drawback that the oscillation threshold current value is increased because light absorption in the current confinement layer is used for transverse mode control.

[0005]

A semiconductor laser of the present invention for solving the above-mentioned problems is a first-conductivity-type GaAs substrate, a first-conductivity-type clad layer, and GaInP or AlG.
an active layer in which a natural superlattice made of aInP is formed;
In the active layer, a double heterostructure in which a conductive clad layer is sequentially stacked is provided, and in the active layer, a region beside the stripe contains impurity atoms and has a large bandgap energy, compared to the inside of the stripe. Conductive type G
The surface orientation of the aAs substrate is characterized in that it is inclined from (001) to the [−110] or [1-10] direction by 0 ° or more and 10 ° or less.

[0006]

When the natural superlattice is disordered by diffusing impurities to the side of the stripe of the active layer in which the natural superlattice made of GaInP or AlGaInP is formed, the bandgap energy is increased and the refractive index is reduced, the inside and the side of the stripe are reduced. Band gap energy difference and refractive index difference between
It contributes to the current constriction and the refractive index difference for controlling the transverse mode.
By this contribution, it is possible to reduce the contribution to the effective refractive index using the conventional light absorption in the current constriction layer, that is, it is possible to separate the current confinement layer from the active layer and reduce the light absorption.

On the other hand, the order of the natural superlattice of GaInP or AlGaInP depends on the growth temperature and (the amount of V group raw material supply) /
In addition to the (group III raw material supply amount) ratio (V / III ratio), it depends on the plane orientation of the substrate (for example, spring 1991 third
Proceedings of the 8th Joint Lecture on Applied Physics, 1st Volume, Lecture No. 30a-ZG-5). That is, if the plane orientation of the GaAs substrate is tilted from (001) in the [-110] or [1-10] direction by 0 ° or more and 10 ° or less, a natural superlattice is easily formed and the bandgap energy is reduced. .. However, the bandgap energy obtained by disordering the natural superlattice by impurities hardly depends on the order of the natural superlattice before disordering, that is, the bandgap energy, and can be determined by the impurity concentration in the active layer. Therefore, compared with the case of using a non-tilted substrate, crystal growth is performed on a GaAs substrate in which the plane orientation is tilted from 0 ° to 10 ° in the [-110] or [1-10] direction. Then, in the active layer, impurities are diffused to the sides of the stripes to disorder the natural superlattice to increase the bandgap energy and reduce the refractive index. The difference in refractive index can be increased. Due to this effect, the current confinement layer can be further separated from the active layer to reduce the light absorption, and eventually a lateral mode semiconductor laser that oscillates at a low threshold value can be obtained.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a semiconductor laser showing one embodiment of the present invention (hatching showing a cut surface is omitted), and FIG. 2 is a manufacturing process diagram of this semiconductor laser. FIG. 1 shows the semiconductor laser of the embodiment cut along a plane perpendicular to the cavity axis.

In the fabrication of this embodiment, first, the growth by the low pressure MOVPE method was performed for the first time, and the growth was performed from (001) to [11].
[0] direction on the n-type GaAs substrate 1 having a plane orientation inclined by 6 °, an n-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 2 (thickness 1 μm), a Ga _0.5 In _0.5 P active layer 3 (thickness 0.07 μm), p-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P
A clad layer 4 (thickness 1 μm), a p-type Ga _0.5 In _0.5 P layer 5, and a p-type GaAs cap layer 6 were sequentially formed (FIG. 2).
(A)). The growth conditions are a temperature of 660 ° C. and a pressure of 70 torr.
r, V / III = 200. As a raw material, TMA
I, TEGa, TMIn, phosphine, arsine, disilane as an n-type dopant, and dimethyl zinc as a p-type dopant were used. On the wafer thus grown, a stripe-shaped SiO ₂ film having a width of 5 μm was formed by photolithography.
A mask 9 was formed (FIG. 2 (b)). Next, this SiO ₂
P-type (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P using mask 9
In the middle of the clad layer 4, etching was performed in a mesa shape up to a distance of 0.4 μm from the active layer. And zinc (Z
By using the mask 9 in the atmosphere of n) and phosphorus (P), Zn is selectively diffused into the active layer in the region other than the stripe to disorder the natural superlattice, and the Zn diffusion region 1
0 was formed (FIG. 2 (c)). Further, Si-doped GaAs was formed by the second MOVPE growth using the same mask 9.
Layer 8 was selectively embedded on both sides of the mesa (Fig. 2).
(D)). Then, the SiO ₂ mask 9 is removed (see FIG.
(E)) p-type GaAs by the third MOVPE growth
The contact layer 7 was formed. After that, an electrode was formed and cleaved to form a laser light emitting end face to complete the semiconductor laser shown in FIG.

The oscillation threshold currents of the semiconductor laser of the present invention and the conventional semiconductor laser thus produced are each 4
5 mA and 55 mA, the semiconductor laser of the present invention has a lower oscillation threshold current value than the conventional one. Further, the semiconductor laser of the present invention lased at a single lateral moat up to 5 mW or more.

[0011]

As described above, according to the present invention, a transverse mode control AlGaInP-based semiconductor laser device having a low absorption of laser light oscillated in the active layer and a low oscillation threshold current value was obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a semiconductor laser of the present invention.

FIG. 2 is a manufacturing process diagram of the semiconductor laser of FIG.

FIG. 3 is a sectional view of a conventional semiconductor laser.

[Explanation of symbols]

1 n-type GaAs substrate having a plane orientation inclined by 6 ° from (001) to [110] 2 n-type AlGaInP clad layer 3 GaInP active layer 4 p-type AlGaInP clad layer 5 p-type GaInP layer 6 p-type GaAs cap layer 7 p Type GaAs contact layer 8 n type GaAs current confinement layer 9 SiO ₂ 10 Zn diffusion region 11 (001) -n type GaAs substrate

Claims (1)

[Claims] 1. A first-conductivity-type clad layer, an active layer in which a natural superlattice of GaInP or AlGaInP is formed, and a second-conductivity-type clad layer are sequentially laminated on a first-conductivity-type GaAs substrate. In the active layer having a double hetero structure, a region beside the stripe in the active layer contains impurity atoms and has a large bandgap energy, the plane orientation of the first conductivity type GaAs substrate is (001 ) To [-110] or [1-1
A semiconductor laser having an inclination of 0 ° or more and 10 ° or less in the [0] direction.