JPH01120884A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To form a semiconductor laser in which only the thickness of a part to be etched is controlled and a lateral mode is preferably controlled with good reproducibility by employing a laminated layer structure of a first semiconductor layer made of a superlattice structure having high etching selectivity and a second semiconductor layer. CONSTITUTION:A P-type photoconductive layer having a superlattice structure made of 27 periods of an undoped Al0.25Ga0.75As active layer 104 as a first semiconductor layer, an Al0.4Ga0.6As barrier layer 105 and an Al0.2Ga0.8As well layer is formed. Further, a P-type Al0.5Ga0.5As clad layer 106 as a second semiconductor layer, a P-type GaAs contact layer 107, and an undoped ZnSe layer 108 as a third semiconductor layer are formed. The layer 108 in such a structure performs as a role of a current constriction and also as a light confinement role. That is, a current flows to a central stripe thereby to reduce a threshold value current, thereby enclosing a light laser-oscillated in the stripe of the layer 104 in the stripe, and stabilizing a lateral mode by a refractive index guiding mechanism.

Description

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

[Conventional technology]

Conventionally, Extended Abstract of [phase]
The Eighteens Co/Fruns On eSolid
State Devices e&Materials 198
6, pages 173-176, and a detailed explanation is shown in Figure 382. FIG. 2 shows a laser emission cross section of a conventional semiconductor laser. ngl(100)GaAs
Substrate 21, n-type GaAs buffer F! J22, n-type Aj
2o, 5iGa, ,s@As cladding layer 23
, p-type GaAs active P324, p-type Aρo, **
Gas, ts As light wave layer 25n! ! Aρ*
-* Gas, S Asff1 flow constriction layer 26, p-type Aρo, tyGaa, ysAS cladding J! 127, p.
It is formed from a WGaAs=i-notact layer 28. Here, n-type AJ2゜1. Gas, sAS current confinement 52B has no knee/ch/g selectivity.
aOs: Etched with HaO solution.

Etching selectivity here means that the current confinement layer 26 is etched selectively with respect to the four-wave optical layer 25, or that it is etched at a high speed.

[Problem that the invention seeks to solve]

However, the conventional semiconductor laser structure lacks etching selectivity. That is, it is extremely difficult to selectively etch two groups having different composition ratios X of A.beta.xGa and -xAs using conventional etchants.

For example, conventional etchants contain mellow or strong hydrogen peroxide solution, so management of the etching solution, i.e., the time from preparation of the etching solution to etching, temperature control of the etching solution, and etching time. There were very troublesome problems such as strict management of

Therefore, in the present invention, in order to solve these conventional problems, we have developed a first etching structure consisting of a superlattice structure with high etching selectivity.
By adopting a structure including a laminated structure of a semiconductor layer and a second semiconductor layer, the thickness of the etched portion can be controlled,
The objective is to provide a semiconductor laser with well-controlled transverse mode with good reproducibility.

[Means for Solving the Problems] In order to solve the above problems, the semiconductor laser of the present invention includes: a first semiconductor layer having a superlattice structure on a semiconductor active layer; A layer structure including a second semiconductor layer disposed on the body layer or in a striped manner, and a third semiconductor layer disposed on the first semiconductor layer and on both sides of the second semiconductor layer. It is characterized by

〔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 a n IJlGa As substrate, 102 is a layer thickness of 0.5
1 layer of μm n-type GaAs buff, 103 has a layer thickness of 1.5 μm
m n-type Aj2*, -s Gas, s AS cladding layer, 104 is an undoped A with a layer thickness of about 0.8 μm,
&. , tsGae, tsAS active layer, 105 is Aρ, ,
a Ga. , sAs barrier layer (60 layers thick), and Aρ.

The p! This is the optical four-wave layer of A, and corresponds to the first semiconductor core described in the claims. 10
B is a p-type Aρ as a ts2 semiconductor layer with a layer thickness of 1.5 μm.

, 1Gae, 6As crab, 107 has a layer thickness of 0.5μ
m p-type GaAs: +7 tact layer, 108 is an undoped Zn5e layer as the third semiconductor layer, 109 is the Ni/AuGe/Au layer of the n-side electrode, 110 is the p-side fff[
This is an AuZn/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 current only through the central stripe section, and in the latter case, the equivalent refractive index of the stripe section is made larger than the equivalent refractive index on both sides of the stripe section. Second, the light lased in the stripe portion of the active layer 104 is confined in the stripe portion, and the transverse mode is stabilized by the four-wave refractive index structure.

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

FIGS. 3(8L) 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
n-type GaAs layer 102, n-type AJ2o on 01
, sGas-sAs cladding layer 103, undoped Aρo, IhGas, tsAs active layer 104, p-type optical waveguide layer 105, p-type AJ2゜,,G
ao,sAs clad T! J106, the p-type GaAs contact layer 107 was formed using metal vapor deposition method (hereinafter referred to as MOCV).
After sequential formation of 5iO-all with a thickness of 3000 nm by MCVD.

In FIG. 3(b), Sin, 111 is converted to Ga'A s substrate 101 by a normal photophosphorography process.
Etch the remaining S s O with a hydrofluoric acid etchant so that it remains in a stripe shape extending in the
* 111 is used as a mask for selective etching of p-type GaAs=+ contact layer 107 and p-type A, 9°, @Gao, * As rad layer 106, and GaAs and AlGaAs are used as masks for selective etching.
The etchant H* SO4: 8H* Os
: p-type Aβ at 8H*O.

sGa*, sAs craft F! Etch to the middle of 110B.

In Figure i3(c), p-type Aj2*, hGa
s,sAs clubto l! 110B and an etchant whose etching rate changes greatly for the p-type optical quartet 105 having a superlattice structure, such as IHF: 5NH, F.
: IH, So, : 8H, O, :
When etched with 8H,O, pHlAl2m,
h Gas , s AS The etching can be easily stopped when the AS cladding layer 106 is exposed and the surface of the p-type optical guide layer 105 is exposed. The etching rate of the AβGaAs superlattice layer p consisting of Al composition ratios of 0°2 and 0.4 is Aρ#, I Gas, s AsF! The etching speed of i is lower than 1/10j2.

In Fig. 3(d), undoped Zn in MOCvD
After performing selective burying growth of the 5e layer 108, the Sio and itt used as selective etch/etch masks were removed with a hydrofluoric acid etchant, and the nfiGaAs substrate 101 was polished to a thickness of 100 μm.
u to FJ III n @ ffi to form the pole 109, and AuZn on the p-type GaAs = + contact ff1107 side.
/Au is vaporized to form a p-side electrode 110, and a semiconductor laser is completed as shown in FIG.

The structure in the growth direction of the semiconductor layer in the stripe portion of this semiconductor laser is usually LOG (large-optical-
It is a structure called Afl, . ,
61m, ss A S activity 1! Light waves from $104 p! ! ! 4 waves of light! By exuding 1105 and applying 4 waves, Al2゜, *5Gas, 6AS activity report 1
By reducing the optical density at 04, it is possible to oscillate more stably to a higher output than a semiconductor laser without a four-wave optical layer. On the other hand, in the direction parallel to the active layer, the transverse mode is controlled by creating an equivalent relative 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.

A p-side electrode 11 is provided between the n-side electrode 108 and the p-side electrode 110.
When a voltage is applied so that 0 becomes positive, current can be injected because a forward bias is applied to the pn junction in the stripe part, but the undoped Zn5e layer 108 has a high resistance on both sides of the stripe part, so no current can be injected. There is almost no flow.

FIG. 4 is a perspective view of a semiconductor laser according to a second embodiment of the invention. The difference from the first embodiment is the shape and formation method of the ribs and the fact that the S i O* film 412 is deposited on the undoped Zn5e layer 408 . 401 is n-type GaAs! Temporarily, 402 is n-type GaAs buff yJ1 with a layer thickness of 0.5 gm.
5.4.03 is ffi thickness 1゜5gm n mA flu
, s G 2L * , s A S class 9F notification, 4
04 is undoped Aβ with a layer thickness of 0.6 μm.

, , Gas-h A' active layer, 405 is Ale
.

s s Gas, s s As barrier ffl (MS
50 people) and AIl*-sh Gas, 7&
Aswell F! ! It is a p-type leading wave layer having a superlattice structure consisting of 30 periods of (ff460), and corresponds to the first semiconductor layer. 406 is a p-layer Aβ as a second semiconductor layer having a layer thickness of 1.5 μm. , sGa. ,,As clubto 35.407 is A! Layer thickness: 5 μm p-type GaAs = +7
408 is an undoped Zn5e layer as the third semiconductor layer.

Chlorine glue active threat ion beam etching was used to form the lipstripes.

In this case, the p-type GaAs contact layer 407 and p! ! !
P-type optical waveguide consisting of superlattice structure for Aρe, 5Gas, sAs craft layer 406! Since the etching speed of 405 becomes low, etching can be easily stopped when the surface of p-type light guide 405 is exposed.

AflGaA consisting of Al composition ratios of 0.25 and 0.86
The etching rate of the s superlattice layer is Al. ,,Ga,,,A
The etching rate is 178 times lower than that of the s-layer.

The resonant laser structure of this semiconductor laser has a four-wave refractive index 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 in the center of the cavity. There is. By configuring such a shape, the longitudinal mode becomes a multiple mode, the astigmatism becomes about 1 μm, it is strong against return light noise, and the laser spot diameter can be narrowed down to about 1 μm using a lens. In other words, f is used for pick-up systems such as magneto-optical disks.
This makes all semiconductor lasers. SfO, g412 is half 4
The current injected into the body laser is passed only through the stripe portion, thereby reducing reactive current and threshold current.

In the above example, AβG was added to the first epitaxial growth layer.
I explained using four aAs/GaAs compounds as an example.
Other ■-V group compound semiconductors or mixed crystals thereof may be used, or Zn5ef may be used to constrict the current in the third semiconductor layer and to provide a difference in equivalent ratio refractive index between the lip stripe and both sides thereof.
Although fl was used, other II-Vl group compound semiconductors and their mixed crystals, and ■-v group compound semiconductors and their mixed crystals may also be used.Although MOCVD was used as the semiconductor formation method, other formation methods may also be used. For example, molecular beam epitaxy may 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 first semiconductor layer has a superlattice structure and a part of the second semiconductor layer is etched so that the surface of the first semiconductor layer is exposed by increasing the etching selectivity with respect to the second 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, fi2 is an emission cross-section of a conventional half-four body laser, and FIGS.
d) is a manufacturing process diagram of the semiconductor laser of the present invention, and FIG. 4 is a perspective view of the semiconductor laser of the present invention, which is different from FIG. 1. 101 , 21 , 401 ・N-type GaAs substrate 102
, 22, 402-n-type GaAs buffer layer 103, 23, 403 - n-type AJ2GaAs cladding layer 104, 404-A IlGaAs active layer 105.25, 405...p-type optical waveguide layer 10Ei ,2
7,408...p-type raft layer 107.28,407
...p-type contact layer 108.408--undoped Z n S e notification 109...n-side electrode 110...n-side electrode 111.412...S i O*24-p-type Ga
A's active layer - 26... n-type AρGaAs current confinement layer or above /I/ Child≠Figure

Claims (1)

[Claims] a first semiconductor layer having a superlattice structure on the semiconductor active layer; a second semiconductor layer having a rib stripe shape 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.