JPH01211990A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To make it possible to eliminate a part of a second semiconductor layer so as to expose the surface of a first semiconductor layer, and control transverse mode with excellent reproducibility, by constituting the second semiconductor layer of superlattice structure, and increasing the etching selection ratio with respect to the first semiconductor layer. CONSTITUTION:A layer structure composed of the following is adopted; a first semiconductor layer 106 having high etching selectivity to interrupt etching, a second semiconductor layer 106 constituted of superlattice structure easy to be etched, and a third semiconductor layer 108 arranged on both sides of the second semiconductor layer 106 on the first semiconductor layer 105. Thereby a semiconductor laser wherein the thickness of etching part is controlled, and the transverse mode is sufficiently controlled can be obtained with excellent reproducibility.

Description

[Detailed Description of the Invention] Industrial Application Field] The present invention relates to a semiconductor laser with a controlled transverse mode, and in particular, by achieving uniformity in the thickness of a semiconductor layer with good reproducibility, the characteristics of the transverse mode, etc. The present invention relates to a semiconductor laser with reduced variation in .

[Conventional technology]

Traditionally, Extended Abstract on the
Eighteenth Conference on Solid State Devices and Materials 1986
The detailed explanation is shown in FIG. 2, which shows a laser emission cross section of a conventional semiconductor laser. n-type (100) GaAs substrate 21.1] type GaAs buffer layer 22, n-type A j o
, ssG a.

bsAB cladding layer 23, p-type GaAs active layer 2
4, ρ type A j 0.25G a 0.7SA S optical waveguide layer 25, n type Aj o, s Gao, s Ast flow constriction layer 26, ρ type A, 11° 27G a o7sA S cladding layer 27, p type It is formed from a GaAS contact layer 28. Here, n-type Aj o, s Gao,
The sAS current confinement layer 26 was etched with a 6H2304:H2022H20 solution with no etching selectivity. Etching selectivity here means that the current confinement layer 26 is etched selectively with respect to the optical waveguide layer 25, or that it is etched at a high speed.

[Problem to be solved by the invention]

However, the conventional semiconductor laser structure lacks etching selectivity. That is, it is extremely difficult to selectively etch two layers of AjzGa+-*AS having different composition ratios X of Aj using a conventional etchant. For example, conventional etchants contain aqueous monoarsenic peroxide, which decomposes easily, so management of the etching solution, that is, the time from preparing the etching solution to performing etching, the temperature control of the etching solution, etc. However, this method had very troublesome problems such as strict control of etching time.

Therefore, in the present invention, in order to solve these conventional problems, a first semiconductor layer with high etching selectivity for stopping etching, and a second semiconductor layer having a superlattice structure that is easily etched are used. By adopting a laminated structure, the thickness of the etched portion can be controlled, and the aim is to provide a semiconductor laser with good control of the transverse mode with good reproducibility.

[Means to solve the problem]

In order to solve the above problems, the semiconductor laser of the present invention includes a first semiconductor layer on a semiconductor active layer, and a rib stripe-shaped superlattice M structure disposed on the first semiconductor layer. It is characterized by including a layer structure consisting of a second semiconductor layer and a third semiconductor layer disposed on the first semiconductor layer and on both sides of the second semiconductor layer.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. 1st
The figure is a cross-sectional view of a semiconductor laser according to the present invention. 101
is an n-type GaAs substrate, and 102 is a fll with a layer thickness of 0.5 μm.
Type GaAs buff, 103 is n-type A with a layer thickness of 1.5 μm.
j o, s G a o s A S cladding layer, 10
4 is an undoped A J olsG with a layer thickness of 0.08 μm.
a 0.75A S active layer 105 has a layer thickness of 0.2μ
This is a p-type AJlo, s Ga O, 7A S optical waveguide layer, and corresponds to the first semiconductor layer described in the claims. 106 is Ajo, b Gao4A s barrier layer (layer thickness 60 layers), A j 0.4 Gao,
b It is a p-type cladding layer consisting of a superlattice structure with a period of 130 of the AS well layer (layer thickness 50 layers), and is the second semiconductor layer, and 107 is a p-type Ga A layer with a layer thickness of 0.5 μffI.
s contact layer, 108 is an undoped Zn5e layer as the third semiconductor layer, 109 is the Ni/N1ll electrode
AuGe/'Au layer 110 is p-side type, flea Au
Zn/Au layer.

In this structure, the Zn5e layer 108 serves as a current confinement because it is a high resistance layer, and also serves as an optical confinement because its refractive index is smaller than that of the p-type cladding layer 106. That is, in the former case, the threshold current is reduced by passing the current only through the central stripe section, and in the latter case, the equal polarized refractive index of the stripe section is compared with the equal polarized refractive index on both sides of the stripe. The laser beam oscillated in the stripe portion of the active layer 104 is confined in the stripe portion, and the transverse mode is stabilized by the refractive index waveguide mechanism.

Next, in order to more clearly explain the construction of the present invention, it will be explained based on manufacturing process diagrams.

FIGS. 3(a) to 3(d) are cross-sectional views sequentially showing the manufacturing process of a semiconductor laser according to the present invention.

In FIG. 3(a), an n-type (100) GaAS substrate 1
01, n-type GaAs buffer layer 102, n-type A j
o, s G a o, s A S cladding layer 103
, undoped A j o, sG a 0.7SA S active layer 104, p-type optical waveguide layer 105, p-type All o,s
A Gao, s As cladding layer 106 and a p-type GaAs contact layer 107 are grown by metal organic vapor phase epitaxy (hereinafter referred to as MO
After sequentially forming by CVD), 300% by thermal CVD
A SiO2 film 111 with a thickness of 0A is deposited.

In FIG. 3(b), 5iOzllll is formed on the GaAs substrate 101 by a normal photolithography process.
Etching is performed using a hydrofluoric acid etchant so that stripes extending in the TT> direction are left, and the remaining 5iOzll is deposited on the p-type GaAs:2 contact layer 107 and the ρ-type cladding layer 1.
GaAs and AJG as selective etching masks for 06
H2SO4, an etchant for aAs: 8H20□
: Etch the ρ-type cladding layer 106 to the middle at 8H20.

In FIG. 3(c), the p-type cladding layer 106 and the p-type optical waveguide layer 105 having a superlattice structure are etched with an etchant whose etching rate changes greatly, such as IHF:5.
Etching with NH,F21H2So, :8H202:8H20 etches the p-type cladding layer 106, and the etching can be easily stopped when the surface of the p-type optical waveguide layer 105 is exposed. The composition ratio of Ajl is 0.
The etching rate of the AN GaAs superlattice layer consisting of 6 and 0.4 is more than 10 times the etching rate of the AJ o, s Gao, t As layer.

In Fig. 3(d), undoped Zn5 is formed by MOCVD.
After selectively filling and growing the e-layer 108, the StO□ 111 used as a selective etching mask is removed with a hydrofluoric acid etchant, and the n-type GaAs substrate 101 is
After polishing to a thickness of 0 μm, N i / A u G
Deposit e/A u and nll! l electrode 109 is formed, and A u Z n is formed on the p-type GaAs contact layer 107 side.
/A, u is evaporated to form a pill electrode 110,
A semiconductor laser is completed as shown in Figure 1.

The structure in the growth direction of the semiconductor layer in the stripe portion of this semiconductor laser is usually LOC (1 arae-optical-
jflj 3u called cavity), and A
II o, + % c a o, 85As active layer 10
By causing the light wave from 4 to leak into the p-type Ajo, 1GaO, 7AS optical waveguide layer 105 and be guided, A J o,
+ sG ao, a5A The light density in the S active layer 104 is lowered, and stable oscillation is possible up to a higher output than a semiconductor laser without an optical waveguide.

On the other hand, in the direction parallel to the active layer, the transverse mode is controlled by providing an equalized refractive index difference between the stripe portion and both sides thereof. Here, by setting the stripe width to about 2 μm, it is possible to obtain the fundamental transverse mode.

When a voltage is applied between the n1llll electrode 109 and the p-side electrode 110 so that the p-side electrode 110 becomes positive, current can be injected in the stripe part because a forward bias is applied to the ρn junction. Since the undoped Zn5e layer 108 has a high resistance on both sides of the region, almost no current flows.

FIG. 4 is a perspective view of a semiconductor laser according to a second embodiment of the invention. The differences from the first embodiment include the shape and formation method of the ribs and the fact that the 5i0-film 412 is an undoped Zn5e layer 40.
It is deposited on 8. 401 is an n-type GaAs substrate, 4
02 is an n-type Ga As buffing layer with a layer thickness of 0.5 μffl, and 403 is an rL type AJ o with a layer thickness of 1°5 μrrt.
, s Gao, s As cladding layer 404 has a layer thickness of 0.
06μm undoped AJo, tsGa 0.75A
The S active layer 405 is a p-type optical waveguide layer with a layer thickness of 0.2 um, and corresponds to the first semiconductor layer.

406 is an AjO, 6Gao4As barrier layer (layer thickness 60
The p-type cladding layer 407 as the second semiconductor layer is composed of a superlattice structure with 130 periods of A j O,4G ao, b A S well layer (layer thickness 50). A .5 μm ρ-type GaAs contact layer 408 is an undoped Zn5C layer as a third semiconductor layer.

The rib stripe formation method uses active chlorine glue.
Ion beam etching was used.

In this case, the p-type Ajo, s Gao, t As optical waveguide 405 is connected to the p-type cladding layer 406 having a superlattice structure.
Since the etching speed of the p-type optical guide layer 4 becomes smaller,
Etching can be easily stopped when the surface of 05 is exposed. The etching rate of the AjGaAs superlattice layer with Aj composition ratios of 0.4 and 0.6 is AN o,s
The etching rate is more than 10 times that of the Gao, tAs layer.

The structure of this semiconductor laser in the cavity direction is of a refractive index waveguide type with a stripe width of 2.5 μm near the cavity end face, and a gain waveguide type with a stripe width of 30 μm at the center of the cavity. . By configuring such a shape, the fir mode becomes a multimode, and the astigmatism is reduced to 1.
It is resistant to return light noise, and the laser spot diameter can be narrowed down to about 1 μm using a lens. In other words, it is a semiconductor laser that is most suitable for use in big-arc systems such as magneto-optical disks. The SiO□WA 412 allows the current injected into the semiconductor laser to flow only through the stripe portion, thereby reducing reactive current and threshold current.

In the above example, AjG is used in the first epitaxial growth layer.
This was explained using an aAs/GaAs compound semiconductor as an example.
Other III-V compound semiconductors or mixed crystals thereof may be used, and Zn5 may be used to constrict the current in the third semiconductor layer and provide an equalized refractive index difference between the rib stripe and both sides thereof.
Although the E layer was used, other n-Vl group compound semiconductors or their mixed crystals, IV group compound semiconductors or their mixed crystals may also be used, and MOCVD was used as the semiconductor formation method, but other Formation methods such as molecular beam epitaxy may also be used.

〔Effect of the invention〕

As explained in detail above, the refractive index difference for stabilizing the transverse mode largely depends on the thickness of the first semiconductor layer.

Therefore, in the present invention, the second semiconductor layer has a superlattice structure and a part of the second semiconductor layer is formed so that the surface of the first semiconductor layer is exposed by increasing the etching selectivity with respect to the first semiconductor layer. This has the effect that the transverse mode can be controlled with good reproducibility.

[Brief explanation of the drawing]

FIG. 1 is an emission cross-sectional view of the semiconductor laser of the present invention, FIG. 2 is an emission cross-section of a conventional semiconductor laser, and FIGS. 3(a) to (d)
) is a manufacturing process diagram of the semiconductor laser of the present invention, and FIG.
It is a perspective view of the semiconductor laser of this invention different from a figure. 101.21.401...n-type GaAs substrate 102.22.402...n-type GaAs buffer r layer 103.23.403...R-type AjGaAs cladding layer 104.404...AjGaAs active layer 105. 25.405...p-type optical waveguide layer 106.27.406...p-type cladding layer 107.28.407...p-type contact layer 108.408...and-1ZnSe layer 109... N-side electrode 110...pf! II electrode 111.412...5iO2 211...p-type GaAs active layer 26...n-type AjG a As current confinement layer and above Applicant: Seiko Epson Corporation

Claims (1)

[Claims] a first semiconductor layer on the semiconductor active layer; a second semiconductor layer having a rib stripe-like superlattice structure disposed on the first semiconductor layer; A semiconductor laser comprising a layer structure including a third semiconductor layer disposed on both sides of a second semiconductor layer.