JPH04127595A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To realize a lateral mode control small in astigmatic difference by a method wherein the injection width of a current in a lateral mode control type AlGaInP semiconductor laser is set much smaller than the width of an effective refractive index distribution provided in parallel with an active layer. CONSTITUTION:An etching process is carried out with a mixed solution of H3PO4, H2O2, and H2O and an etching solution of H2SO4 as far as a halfway point of a P-(Al0.6Ga0.4)0.5In0.5P clad layer 15, and the clad layer 15 is set as thick as 0.2-0.3mum on both the sides of a stripe-like mesa. Only a P-Ga0.5In0.5P car layer 16 is selectively etched with the mixed solution of H3PO4, H2O2, and H2O to enable the width B of the cap layer 16 to be smaller than the width A of the upper part of the clad layer 15 of the stripe-like mesa by the control of side etching. At this point, as the injection width A of a current for laser oscillation is set much smaller than the width C of an effective refractive index distribution provided in parallel with the active layer 14, the wave front of laser rays is small in distortion and the astigmatic difference becomes smaller than 5mum.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a semiconductor laser used for barcode readers such as POS and FA systems, and as a light source for laser printers, etc., and particularly relates to a semiconductor laser that is capable of high output and transverse mode control. Yes, AJ with oscillation wavelength of 680 nm or less with small beam astigmatism difference
This invention relates to the structure of a GaInP-based visible light semiconductor laser.

[Conventional technology]

Figure 3 shows the conventional transverse mode control type A il Ga I
It is a cross-sectional view showing the structure of an nP-based visible light semiconductor laser (Proceedings of the Japan Society of Applied Physics Fall 1986, p.

165).

1 in the figure is an n-GaAs substrate, and on this substrate 1 there is an n-GaAs substrate.
- A GaAs buffer layer 2 is formed. On the buffer layer 2 is an n-AAGaTnP cladding layer 3. GaT
nP active layer 4, p-AnGalnP cladding layer 5. p-
GaTnP cap layer6. A double heterojunction structure consisting of an n-GaAs current element layer 7 and a p-GaAs contact layer 8 is formed.

Crystals for semiconductor lasers with this structure are usually MOVPE.
A is manufactured by the method, but A,
Since it is technically difficult to stack &Ga1nP, as shown in FIG. By forming the n-GaAS current blocking layer 7, current confinement and optical waveguide effects are achieved in a self-aligned manner.

Here, the manufacturing process for the conventional structure shown in FIG. 3 will be briefly described. First, by the first MOVPE growth, n-Ga
A five-layer structure from As buffer layer 2 to p-GaInP cap layer 6 is sequentially formed. Subsequently, on the cap layer 6, a stripe-shaped S i 0 with a width of 5 μm is formed by photolithography.
A two-layer mask is formed, and the p-AJ2Ga I nP cladding layer 5 is etched halfway to form a striped mesa portion.Then, a second MOVPE growth is performed to form a striped 5102M! nG in the mesa area excluding the mask
An aAs current blocking layer 7 is selectively formed. After that, 5i
After removing the 02 film mask, a p-GaAs contact layer 8 is grown over the entire surface by a third MOVPE growth, and a p-side electrode 9 is formed on the contact N8. n-GaAs substrate 1
By forming the n-side electrode 10 thereon, a semiconductor laser having the structure shown in FIG. 3 is completed.

In this WI structure, current confinement is performed by a D-GaAs current block N7. The p-GaInP capping layer 6 is composed of the p-AρGaInP cladding layer 5 and the p-GaInP capping layer 6.
It has the role of preventing an increase in electrical resistance caused by band discontinuity with the S contact layer 8 (for example, 1985 Autumn Proceedings of the Japan Society of Applied Physics P, 765 Lecture No. 19a-
ZR-6).

On the other hand, the transverse mode control is performed using p-AηGa1nP with steps.
This is achieved by forming a refractive index distribution on both sides of the mesa since light is absorbed by the nGaAs current blocking layer 7 on both sides of the mesa of the cladding layer 5.

[Problem to be solved by the invention]

In recent years, there has been an increasing demand for an index-guided semiconductor laser that oscillates in a fundamental transverse mode, has a low oscillation threshold, and has a low astigmatism difference.

However, in the conventional refractive index guided semiconductor laser as described above, the current injection width for laser oscillation and the width of the built-in effective refractive index distribution in the direction parallel to the active layer 4 are approximately the same size. Distortion of the wavefront occurs, and the astigmatism difference is 1
It has a drawback that it is large, ranging from 0 to 13 μm, and it is difficult to narrow down the laser beam to a minute spot.

The present invention solves these problems and provides an AjIGalnP visible light semiconductor laser that is capable of transverse mode control with a small astigmatism difference.

[Means to solve the problem]

The semiconductor laser of the present invention is a conventional transverse mode control type AJ.
In order to make the current injection width in the Ga I nP semiconductor laser sufficiently smaller than the width of the built-in effective refractive index distribution in the direction parallel to the active layer, the width of the uppermost cap layer formed in the first MOVPE growth is It has a mesa portion that is smaller in width than the cladding layer, which is the underlying layer.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a cross-sectional view showing the structure of a semiconductor laser according to an embodiment of the present invention.

First, the n-
GaAs substrate 11 (n concentration 2 x 10 I8c m-
') Thickness 0.5 on top. czm n-GaAs buffer layer 12 (n concentration 1×I Q 17 cm −3), 1 μm thick n-(A, &(1,6Gaa4)o, q I
no, q P cladding layer 13 (n concentration 5x 10"c
m-3), Gao with a thickness of 0.06 μm, 5 T no,
5P active layer 14. 1 μm thick p(A II 6,6
G ao4) 0.5 I no5P cladding layer 15
(p concentration 3×10'7 cm-') is sequentially grown to form a double hetero wafer. Subsequently, the cap layer 16
A striped Si with a width of 5 μm is formed on the top by photolithography.
Form an O2 film mask.

Next, as shown in FIG. 1, H, PO4H202, H
The p-(Aρ0,6 Ga(1,4).'5InO6p cladding layer 15 is etched to the middle using an etching solution of 20 mixed i and H2SO4 to reduce the thickness of the cladding layer 15 on both sides of the striped mesa part. 0.2~0.3μ
Control is performed so that m. Next, H8P 04, H
pGao, 5 I n using a mixture of 202 and H20
o, 5 Only the P character 1 layer 16 is selectively etched, and as shown in FIG. The width B (shown in the figure) is narrowed by controlling the amount of side etching. Here, the width A was 5 μm and the width B was 3 μm.

Next, by second M○VPE growth, a 0.6tt thick layer was formed on the mesa area excluding the striped 5iOzllu mask.
An n-GaAs current blocking layer 17 (n concentration I x 1018 cm-') of m (flat portion) is selectively grown. After that, after removing the Si02 film mask, a 3 μm thick p-GaA film was grown on the entire surface by the third MOVPE growth.
S contact layer 18 (p concentration 5 x 1018c m-
') Grow and form a P-side type 119n on the contact layer 18.
- By forming the n-side electrode 20 on the GaAs substrate 11, the semiconductor laser of the present invention is completed.

Here, the current injection width A for laser oscillation is
Since the width C of the built-in effective refractive index distribution in the direction parallel to is sufficiently small compared to the width C of the built-in effective refractive index distribution, the distortion of the wavefront of the slanted laser beam becomes small, and the astigmatism difference becomes small to 5 μm or less.

Therefore, it becomes possible to narrow down the laser beam to a minute spot of about 17 zm.

FIG. 2 is a cross-sectional view of Embodiment 2 of the present invention.

The growth of the double heterostructure by MOVPE is carried out in the same manner as in the previous embodiment.

Here, p-(A,
(10,6Ga,,4)0.5I nO,5P
In the middle of the cladding layer 15, there is a p-Gao layer with a thickness of 40^, 5
I no, sP etching stop layer 21 (p concentration 3×10
This embodiment differs from the above-mentioned embodiment 1 in that the film is grown and formed.Other than this, it is the same as the above-mentioned embodiment.

In this embodiment, since the etching stop layer 21 is formed, the PCA on both sides of the striped mesa portion is
l1o, b Gao, a > 0.5 I no, s
This has the advantage that the thickness of the P cladding layer 15 can be manufactured with good controllability by utilizing the etching stop property.

Further, the thickness of the etching stop layer 21 is set to be as thin as 40 Å in order to prevent the laser oscillation light from being absorbed.

〔Effect of the invention〕

As explained above, according to the present invention, since the width of the built-in effective refractive index distribution in the direction parallel to the active layer 14 is sufficiently wider than the current injection width, the distortion of the wavefront of the laser beam is small and the astigmatism The distance difference is reduced to 5 μm or less, and a tank mode controlled laser that oscillates in the fundamental transverse mode and has a low astigmatism difference can be realized.

Furthermore, by reducing the current injection width, fundamental transverse mode oscillation can be maintained even during high output operation, and a low oscillation threshold current can be achieved.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are AAGaInP showing an embodiment of the present invention.
FIG. 3 shows a cross-sectional view of a conventional semiconductor laser. In the figure, ],] ]1---n-GaAs substrate 2.12・nG
aAs buffer layer, 3-n-AJ! GaInP cladding layer, 4...GaInP active layer, 5...
・p-AJ2GaInP cladding layer, 6-p-GaI
nP cap layer, 7,17...n-GaAs current blocking layer, 8.18-...-p-GaAs contact layer, 9°1
9.p electrode, 10.20.-n electrode, 13.n(A
no6Ga0.4 ) o, s I no5P cladding layer, ] 4-Gao, q T no, 5 P active layer, 15
-p(A!2.), 6 Ga, ), 4) o, 5 I
no, 5 P cladding layer, l 6-・-p-GaO, 5
I no, 5 P cap layer, 21-p-○a, 5
I no and 5 P etch stop layers are shown, respectively.

Claims (1)

[Claims] The double heterojunction structure formed on the semiconductor substrate is (A
j_XGa_1_−_X)_0_. _5In_0_. ＿
In a 5P-based semiconductor laser, at least an active layer is sandwiched between a first cladding layer of a first conductivity type and a second cladding layer having a striped mesa shape of a second conductivity type;
The mesa shape width of the third semiconductor layer laminated on the upper part of the cladding layer is narrower than the mesa shape width of the underlying second cladding layer, and the surface of the second cladding layer excluding the semiconductor layer has a first conductivity type and a refractive index higher than that of the active layer. 1. A semiconductor laser comprising: a fourth semiconductor layer having a large diameter; and current is injected from the third semiconductor layer.