JPS63169785A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser which has low oscillation threshold value and high reliability by averaging the composition a superlattice layer to become an active region except a stripelike region by an impurity diffusing or ion implanting process. CONSTITUTION:An N-type Al0.45Ga0.55As layer 2, a superlattice layer 3 in which an AlAs layer and a GaAs layer are alternately laminated, a P-type Al0.45Ga0.55 As layer 4 and a P-type GaAs layer 5 are sequentially formed on an N-type GaAs substrate 1 by a first MOVPE growth. Then, with an SiO2 film as a mask a stripelike region remains, a Zn-diffused layer 6 of the depth arriving at the layer 3 is formed, and the composition of the layer 3 is averaged. Thereafter, with an SiO2 film 10 as a mask it is selectively etched to the depth which does not arrive at the layer 3 to form a mesa 11. Further, an N-type GaAs 7 is formed by a second MOVPE growth, and a P-type electrode and an N-type electrode are eventually formed. According to this method, a semiconductor laser having lower oscillation threshold and high reliability can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method of manufacturing a semiconductor laser that can produce a semiconductor laser with a low operating current and a radiation beam whose cross-sectional shape is close to circular with high mass productivity. .

(Prior art) Here, metal organic vapor phase epitaxy
cV1-0r Phase Epitaxy method, hereinafter M
AJI GaAs/Ga using OVPE method)
This will be explained by taking an As semiconductor laser as an example. FIG. 3 shows the structure of a semiconductor laser according to the prior art (for example, an IEDM).
'83 Proceedings spp292-295
'), and FIG. 4 is a cross-sectional view showing the manufacturing process. An n-type All a , a gGas , @JIB layer 13 , AQ e , 15GJle, and sJS active layer 14 are formed on an n-type GaAs substrate 12 by the MOVPE method.
, p-type AQ*, agGas, ssAs layer 15, and n-type GaAs current blocking layer 16 are sequentially laminated (FIG. 4(a)), and a groove 17 penetrating the n-type GaAs current blocking layer 16 is formed by selective etching. (Fig. 4(b)), and then p-type AJI@
, 4 BGa,..., As layer 18, p-type GaAs layer 19 are formed (FIG. 4(C)), and finally p electrode 20, n
The semiconductor laser shown in FIG. 3 is completed by forming the t-electrode 21 (
(FIG. 3), current confinement is performed by the current blocking layer 16, and the transverse mode of the laser beam is set as the fundamental mode due to the difference in effective refractive index and light absorption rate between the region of the groove 17 and other regions.

(Problems to be Solved by the Invention) In this semiconductor laser, the laser beam is largely absorbed in the region in contact with the groove 17, so the transverse mode is stabilized, but on the other hand, the oscillation threshold cannot be made very small, and The differential quantum efficiency is also low.If the width of the groove 17 is determined so that the threshold value is the minimum, the laser beam will become an elongated ellipse in the direction perpendicular to the active layer.In addition, regarding current confinement, the laser beam will be in contact with the groove 17. p-type All*, a5Gas
, s iAsAs layering 5 causes the current to spread, so in order to reduce the oscillation threshold, p-type AJI e ,
It is necessary to make a 5GJi*, s 1Asya15 thinner, but at this time the laser light undergoes even greater absorption, so the oscillation threshold does not decrease.Furthermore, with conventional manufacturing methods, p-type u*, asGae, 5sA9J11B and p-type The GaAs layer 19 is a p-type Aj that is exposed to the atmosphere and oxidized.
Since it is formed on the lo, asGae, and asAs layers 15, the growth layer contains crystal dislocations, and the p-type Ajl
e, 4sGa*, aaIf the oxidation of the aaAs layer 15 is severe, negative resistance is observed in the current-voltage characteristics of the laser.

Therefore, an object of the present invention is to provide a method for obtaining a semiconductor laser that oscillates in the fundamental transverse mode, has a low oscillation threshold, and is highly reliable.

(Means for Solving the Problems) A method for manufacturing a semiconductor laser according to the present invention includes forming a first semiconductor layer of a first conductivity type on a semiconductor substrate of a first conductivity type; a superlattice layer formed by alternately stacking an active layer with a small bandgap and a second semiconductor layer with a larger band gap than the active layer, wherein the active layer and the second semiconductor layer each have a layer thickness of 200 Å or less; a first crystal growth step of forming a semiconductor substrate crystal by sequentially growing a third semiconductor layer of a second conductivity type having a larger band gap than the active layer; and a region other than the striped region of the semiconductor substrate crystal. a step of averaging the composition of the superlattice layer by diffusing impurities of a second conductivity type or implanting ions to a depth reaching the superlattice layer; This third without penetrating
an etching step for selectively etching to a depth halfway through the semiconductor layer; and a second step for selectively forming a semiconductor layer including a high resistance or first conductivity type semiconductor layer in areas other than the striped area. and a crystal growth step.

(Function) In the present invention, the composition of the superlattice layer serving as the active region is averaged by an impurity diffusion or ion implantation process, except for the striped region. Since the superlattice layer has a higher refractive index than the averaging layer formed in this way, in the semiconductor laser that can be formed by the method of the present invention, a step in the refractive index is formed in the horizontal direction in the active region. That is,
In this semiconductor laser, laser light is guided into the active region both horizontally and vertically due to the difference in refractive index, making it possible to form a circular laser beam. Further, since the region into which impurities of the first conductivity type are diffused or ions are implanted is in contact with the semiconductor layer of the first conductivity type, a silicon risk is formed, and current can be effectively constricted in the active region.

(Example) FIG. 1 is a cross-sectional view showing an example of the structure of a semiconductor laser obtained by the method of manufacturing a semiconductor laser according to the present invention;
FIGS. 2(1m) to 2(d) are process diagrams showing the manufacturing method. First, a first MOVPE growth is performed to grow n-type GaA.
n-type A11o, 4gGa*, gsAs layer 2 on s-substrate 1
, AjlAs layer with a layer thickness of 80 people and GaAs1 layer with a layer thickness of 80 people.
superlattice layer 3, p-type Ajls, 4s
Ga*, 11A! S layer 4 and p-type GaAsM5 are sequentially formed (2nd!50(a)), -q, 5i0* film 1
0 as a mask, a Zn diffusion layer 6 is formed deep enough to reach the superlattice layer 3, leaving a stripe-shaped region, and the composition of the superlattice layer 3 is averaged (Fig. 2(b)). , SiO□
Using the film 10 as a mask, selective etching is performed to a depth that does not reach the superlattice layer 3 to form a mesa 11 (see FIG. 2).
C)), and further performs a second MOVPE growth to form n-type G.
aAs 7 is formed (Fig. 2(d)), and finally a p-electrode! 8
, nt electrodes are formed to complete the semiconductor laser (FIG. 1).

In the semiconductor laser of FIG. 1 manufactured by applying the present invention, Zn is diffused from the superlattice layer 3 to form the superlattice HJ.
Since the refractive index of the Zn diffused layer 6, which averages the m composition of 3, is smaller, there is a difference in the refractive index in the horizontal direction of the active region.Therefore, the active layer is guided in both the horizontal and vertical directions. This structure has small astigmatism and a stable fundamental transverse mode. By controlling the width of Zn diffusion, the cross-sectional shape of the laser beam can also be made circular. Furthermore, since the n-type Ajl*, asGao, 5gAs layer 2, Zn diffusion layer 6, and n-type GaAs 7 form an NPN silicon layer, they become a current blocking layer. Therefore, the first
In the semiconductor laser shown in the figure, both carriers and light are effectively confined in the active region, the oscillation threshold is low, and stable fundamental transverse mode oscillation can be performed up to a high optical output. Furthermore, in the manufacturing process of the present invention, the active region is not exposed to the atmosphere and oxidized, making it possible to obtain a highly reliable semiconductor laser. In addition, in the description of the present invention, AjlGaAs/GaAs using the MOVPE method
Although the present invention has been explained using a semiconductor laser as an example, it goes without saying that the present invention can be applied to semiconductor lasers made of other materials using a normal phase outer length method or a molecular beam epitaxial method other than the MOVPE method.

(Effects of the Invention) As described above, according to the method of the present invention, a semiconductor laser that oscillates in the fundamental transverse mode, has a low oscillation threshold, and is highly reliable can be manufactured.

[Brief explanation of the drawing]

1IyJ is a cross-sectional view showing an example of a semiconductor laser obtained by the manufacturing method of the present invention, FIG. 2 is a process diagram showing an example of the manufacturing method, and FIG. 3 is a cross-sectional view showing an example of the structure of a semiconductor laser according to the prior art. 4 are process diagrams showing a method of manufacturing the structure shown in FIG. 3. 1, 12... n-type GaAs substrate, 2, 13...
n-type M8. . Gae1gJ3 layer, 3... superlattice layer, 4, 15,
1g”-p type Aj)o, asGao, 5gAs layer, 5
, 19-p-type GaAs layer, 6... impurity diffusion layer, 7,
16=n-type GaAs calendar, 8, 20-p electrode, 9, 2
1...n electrode, 10...5tOa film, 11/'su, 14'''/'Jle, taGa*, aiAS active layer,
17 river ditch.

Claims (1)

[Claims] A first semiconductor layer of a first conductivity type, an active layer having a smaller bandgap than the first semiconductor layer, and a second semiconductor layer having a larger bandgap than the active layer are formed on a semiconductor substrate of a first conductivity type.
The active layer and the second semiconductor layer are alternately laminated with semiconductor layers.
A first semiconductor substrate crystal is formed by sequentially growing a superlattice layer in which each of the semiconductor layers has a thickness of 200 Å or less and a third semiconductor layer of a second conductivity type having a larger band gap than the active layer. and averaging the composition of the superlattice layer by diffusing impurities of a second conductivity type or implanting ions into regions other than the striped regions of the semiconductor substrate crystal to a depth that reaches the superlattice layer. an etching step of etching selectively to a depth halfway through the third semiconductor layer without penetrating the third semiconductor layer while leaving the striped region; a second crystal growth step of selectively forming a semiconductor layer including a high resistance or first conductivity type semiconductor layer in the region.