JPS596588A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To offer a BH-LD of high manufacturing yield with less dispersion of characteristics by a method wherein the height of a mesa stripe is constituted higher than that of multilayer films on both sides of grooves by forming a fixed semiconductor layer only on the upper side of the mesa stripe. CONSTITUTION:An N-InP buffer layer 2, a non doped active layer 3, a melt back prevention layer 4 as a second semiconductor layer and a P-InP clad layer 5 as a first semiconductor layer are successively laminated on an N-InP substrate 1. The mesa stripe 9 is first formed at a part wherein the P-InP clad layer 5 which is previously covered with an etching mask 6 remains, and the etching grooves 7 and 8 are so formed that the P-InP clad layer 5 does not remain on both side distant from the mesa stripe. In burying growth, both of a P-InP current block layer 10 and an N-InP current block layer 11 are so laminted as not to cover the upper surface of the mesa stripe 9, and further a P-InP buried layer 12 and an electrode layer 13 are laminated over the entire surface. Next, the BH-LD is obtained by forming a P type ohmic electrode 14 and an N type ohmic electrode 15.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a structure in which the active layer is surrounded by a large energy gear.
The present invention relates to a semiconductor laser having a buried-chill structure filled with a semiconductor material having a small refractive index, and particularly to a semiconductor laser with improved manufacturing yield.

Generally, a buried heterostructure semiconductor laser (hereinafter referred to as BH-
The LD (LD) has attracted attention as a light source for optical 7-IPA communication because it has excellent characteristics such as a low oscillation threshold, a stabilized oscillation transverse mode, and the ability to operate at high temperatures. The inventors of the present application have disclosed in Japanese Patent Application No. 56-166666 that a BH- I applied for LD. This BH-
LDs have excellent temperature characteristics, are less susceptible to damage during various substrate processing processes, and have improved manufacturing yields. However, this BH-LD structure has the disadvantage that the n-InP current block layer does not grow smoothly and is interrupted on both sides of the trench between the mesa stripes, leading to variations in characteristics. Ta. In addition, in order to prevent this drawback, if you try to grow a thick layer of p-InP current block two layers and two InP current block layers, the n-InP current block layer will cover the top of the mesa stripe containing the active layer that undergoes luminescent recombination. There was a drawback that

An object of the present invention is to eliminate these drawbacks, provide a BH-LD with less variation in characteristics, and a high manufacturing yield.

The structure of the present invention is to provide a multilayer structure semiconductor wafer in which a semiconductor multilayer film including an active layer is laminated on a semiconductor substrate, and a mesa stripe sandwiched between two parallel grooves formed deeper than the active layer. In a buried heterostructure semiconductor laser formed by forming a mesa stripe and growing the mesa stripe, a predetermined semiconductor layer is formed only on the upper side of the active layer of the mesa stripe, and the height of the mesa stripe is adjusted to the image side of the groove. It is characterized by being constructed higher than a multilayer film.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 (alt (b+, (cl) is a cross-sectional view shown in the order of manufacturing steps of the first embodiment of the present invention. First, as shown in FIG. 1(a), (100) n-InP On the substrate 1, an n-InP buffer layer 2, a phase 10 active N3 with an emission wavelength of 1.55 μm, and a second semiconductor layer with emission wavelengths 1 and 3.
p-Ino, yz Gao, z corresponding to ti m
The sAso, alpo, s* meltback prevention layers 4 and the p-InP layer 5, which is the first semiconductor layer, are laminated in this order.

Here Ino, se Qaa4t Asaso
P (LIO active layer 3 has a thickness of 0.15 μm, p-111o
, y2Qaα211 Aso, alpo, ss The meltback prevention layer 4 has a thickness of 0.3 μm% The p-InP cladding layer 5 has a thickness of about 1 μm. An etching mask 6 having a width of about 15 μm is formed in parallel to the <011> direction on the multilayer structure semiconductor wafer laminated in this manner, and the p-InP cladding layer 5 other than the portion covered by this etching mask 6 is selectively etched. Remove. For this selective etching, a small solution of HCJ-based elatin, which can etch InP, may be used. For example, 4H(J+H,0
By etching between 3C and 19 using a mixed etching solution of
The nP cladding layer 5 can be processed and removed.

At this time, p-Inayz Gaazs Aso, a
The anti-etching layer 4 is not etched at all, and the etching can be stopped at the interface between these two semiconductor layers.

Next, as shown in FIG. 1, etching grooves and mesa stripes are formed using a conventional photoresist technique. First, the mesa stripe 9 with a width of 2 μm is formed by forming the p-InP cladding layer 5 which was previously covered with the etching mask 6.
are formed in the remaining portions of the etching grooves 7 and 8.
The width of the mesa stripe 9 is approximately 10 .mu.m, and the p-InP layer 5 is not left on either side of the mesa stripe 9. This needs to be etched deeper than active layer 3, but
Etching can be easily performed with good reproducibility using a Br methanol-based etching solution. For example, etching can be carried out in 3 minutes at 3C using a mixed etching solution consisting of 50 cc of methyl alcohol and 1 cc of BrO.

Finally, as shown in FIG. 1(C), a buried growth electrode is formed. In buried growth, p-InP current pro, reHA 10. The n-InP current shield layer 11 is laminated so as not to cross the upper surface of the mesa stripe 9, and the p-InP buried layer 12 has p-Ino, t 2 Qao, which corresponds to the emission wavelength of 1.3 μm,
zs-Asae! Po, m * 91 pole r @ 13
Make a p-Cff layer on the entire surface.
The InP current blocking layer 10 and the n-InP current shielding layer 22 layer 11 are laminated except for only the upper surface of the stripe 9 (this is detailed in Japanese Patent Application No. 166666/1983). This can be done easily and with good reproducibility by using a two-phase solution method in which an InP source is floating in an In melt. Next, a BH-LD can be obtained by forming a p-type ohmic electrode 14 and an n-type ohmic electrode 15.

In this first embodiment, only the mesa stripe 9 includes the p-InP cladding layer 5 with a thickness of 1 μm, and the mesa stripe 9 is formed 1 μm higher than the portions on both sides of the etching grooves 7 and 8. ing. p-Ino, yzGao, zsAs of the third semiconductor layer is formed so that this mesa stripe 9 is formed 1 μm higher than its surroundings.
cLatPo,ss A meltback prevention layer 4 is formed, and therefore selective etching plays a major role. For this reason, in the buried growth, the two current conductor layers do not cover the upper surface of the mesa stripe 9, and moreover, the etched groove 7. It can be grown smoothly without interruption on both sides of the tree. That is, by forming only the mesa stripe 9 to be higher than its surroundings by lltm using selective etching, the tolerance in forming the current block layer during buried growth is greatly improved, and the BH-
The reproducibility of the LD characteristics can be improved and the manufacturing yield can be greatly improved.

Figure 2 (al, (bl) is a distributed feedback buried heterolaser (DFB-BHLD) which is the second embodiment of the present invention.
FIG. 2 is a cross-sectional view in a direction perpendicular to the resonance axis of the semiconductor device and a cross-sectional view in a direction parallel to the resonance axis of the semiconductor device. K to obtain this DFB-BHLD is first a (Zoo)n-InP substrate 1 and a diffraction grating 2.
form 2. In this diffraction grating 22, the resonance axis direction of the DFB mode is repeated parallel to (011),
The pitch may be an integral multiple of A of the oscillation wavelength in the active layer. For example, using the laser interferometry of He-Cd gas laser and the ordinary chemical etching method, the pitch is 0.40μ.
m, a diffraction grating with a depth of 0.12 μm can be created. On the n-InP substrate 1 on which such a diffraction grating 22 is formed, H-IHo and soGao corresponding to an emission wavelength of 1.05 μm are placed.
, 1IA80.24P0.76 light guide layer 23 with thickness 0
．． Non-doped I corresponding to 3 μm 1 emission wavelength 1°3 μm
no, yzGao, zsAs aatpast active layer 2
4 has a thickness of 0.1 μm, and p-InP is the second semiconductor layer.
The cladding layer 25 has a thickness of 0.8 μm and a first semiconductor layer corresponding to an emission wavelength of 1.2 μm.
Aso, n5Po, and sz layers 26 are sequentially laminated to a thickness of 0.8 μm. In the multilayer structure semiconductor wafer obtained in this way, p-I was applied, leaving only the stripes of @15 μm around the part that would become the mesa stripe, as in the first example.
no, ys C3Bo2zAso, aspo, sz layer 26 is etched off. Etching can also be stopped on the upper surface of the p-InP crat layer 25 by selective etching. For example, sulfuric acid-based mixed Elachan)
Etching is performed for 4001 minutes using 5H, 80, +H10, +H1O.

Next, two etched grooves 7 and 8 and a mesa stripe 9 parallel to the <011> direction are formed in the same manner.

At this time, as in the first embodiment, only the mesa stripe 9 is p
-In(L78Gao, z 2AS0.48PO, lI
Etching is performed to include two layers 26. Finally, buried growth is performed and p-InP current current clock 2 layer 1
0tnnP current current clock 2 layer 11 is also shifted except for the top surface of mesa stripe 9, and further p-InP buried layer 1
21 corresponding to emission wavelength 1.3 μm p-Ino, yz
Qao, zsAso, aIPo, and as electrode layers 13 are sequentially laminated over the entire surface.

In this second embodiment as well, only the mesa stripe 9 has a p-Ino material, compared to the parts on both sides of the grooves 7 and 8.
,ysGao,z2AS0.48PO,! Since the current blocking layer is formed as high as 12 mm (0.8 μm), it is easy to form the current blocking layer, and the manufacturing yield is greatly improved. Furthermore, in order to prevent the appearance of the Fabry-Bello resonance mode, a non-injected region is partially formed or the reflection at the end face is appropriately reduced in order to prevent reflection from at least one end face. In this embodiment, as shown in Figure 9, one end surface 27 is etched with an incline.
Eliminates reflection of laser light from one end face.

The DFB-BHLD made in this way has a CW oscillation threshold current of 40 mA at room temperature, a differential quantum efficiency of 40%,
The wavelength temperature dependence of DFB mode is 0.8X/d e
g, and can be obtained with good reproducibility. In this second embodiment as well, only the mesa stripe 9 is made of p-Ina, ysGao, zzAs with a thickness of 0.8 μm as the first semiconductor layer.
o, 4sPo, s2F@26, the tolerance for buried growth is increased, and the two current hook layers cover the upper surface of the mesa stripe 9, which may cause the etching grooves 7. This makes it easy to grow the crystals in a discontinuous manner, greatly improving manufacturing yields.

Note that this embodiment uses an InP substrate and an old-xGaxAsy
Although an optical semiconductor device with a wavelength band of 1 μm using a P1-y active layer has been shown, the semiconductor material used is not limited to this. Although the end face was etched diagonally, there are methods in which the p-type impurity is diffused only in the injection region of the n-type electrode layer, or the width of the etching groove is narrowed only near one end face, so that the current blocking layer forms a mesa stripe only in this part. It is also possible to use methods such as growing the material so as to cover it to form a non-implanted region. In addition, in Examples (・te is p-InP
, two current blocking layers of n-InP were laminated, but
In addition to the mesa stripe, impurity diffusion may be performed in advance on the semiconductor wafer after mesa etching to laminate a single current blocking layer. −.

We have shown two types of BHLD semiconductor lasers, but these include optical performance devices such as optical bistable devices that use H-LD as a basic device, or composite types that monolithically combine BH-LDs, PDs, FETs, etc. Of course, it can also be quickly applied to optical semiconductor devices.

A feature of the present invention is that in the semiconductor wafer before buried growth, only the mesa stripe has the first semiconductor layer, and the thickness of the first semiconductor layer is larger than the thickness of the mesa stripe on both sides of the etching groove. However, because the mesa stripes are formed high, during buried growth, the current blocking layer does not cover the top surface of the mesa, and at the same time, there is no possibility that the current blocking layer will grow at both sides of the two etched grooves. The tolerance of current block layer growth is greatly improved, and B
The reproducibility of characteristics and manufacturing yield in H-LD are greatly improved.

[Brief explanation of drawings]

Figure 1 (a), (b), (cl is a cross-sectional view shown in the order of manufacturing steps of the first embodiment of the present invention, Figure 2 (al, (
bl is a cross-sectional view of the second embodiment of the present invention and a cross-sectional view of the mesa stripe in the direction of the resonance axis. In the figure, 1...n-■nP substrate, 2...n-I
nP buffer layer, 3--...-Ino, 5sGaα4
1ASO, 1lopolo active layer, 4...p
-In0. y zQao, z 5Aso, a tPo,
s *Melt, (slip prevention layer, 5...p-techn
P cladding layer, 6... Etching mask, 7.8...
...Etching groove, 9 mesa stripes, 10...
...p-InP current current clock 2 layers 1......n
-InP current current clock 2 layers 12...p-In
P buried layer, 13-=-p-In O, 72GaO,
2! l A S 0.6 l p a 39 electrode layers, 1
4. Fist...p-type ohmic electrode, 15...
N-type ohmic electrode, 22...diffraction grating, 23 ・-
----n-Ino, a *Gao, t xAso, z
4Pθ76 light guide layer, 24----InoFzQa
o, zs AsO, 1lIP0.39 active layer, 25
・----p-InP cladding layer, 26---
・-p-Ino, tsQBo, zzAso4g Po
, 82 layers, 27... are etched surfaces.

Claims (1)

[Claims] A mesa stripe sandwiched between two parallel grooves formed deeper than the active layer is formed on a multi-1M structure semiconductor wafer in which a semiconductor multilayer film including an active layer is laminated on a semiconductor substrate. In a semiconductor laser with a buried heterostructure formed by growing a stripe in a buried manner, a predetermined intermediate conductor layer is formed only above the active layer of the mesa stripe to adjust the height of the mesa stripe to a multilayer film on both sides of the groove. A semiconductor laser characterized by having a structure higher than that of the semiconductor laser.