JPH084185B2 - Method of manufacturing embedded semiconductor laser device - Google Patents

Description

The present invention relates to a method for manufacturing an embedded semiconductor laser device.

[Conventional technology]

Liquid-phase epitaxy (LPE), vapor-phase epitaxy (VPE), and molecular beam epitaxy (MBE) are available as double-heterojunction crystal growth methods required for embedded semiconductor laser devices. Among these methods, the metal organic chemical vapor deposition (MOCVD) method is a crystal growth method that is attracting attention because it has excellent mass productivity and excellent controllability of film thickness and composition. The manufacturing process of the buried type semiconductor laser device using this MOCVD method is, for example, as shown in FIGS. 2 (a) to 2 (c), an n-type InP substrate (1).
An n-type InP clad layer (2) is formed thereon, a non-doped GaInAsP active layer (3) is formed on the clad layer, and a P-type InP clad layer (4) layer is formed on the active layer. Next, after forming a SiO ₂ film (5) on the p-type InP clad layer, mesa etching is performed by a wet etching method to remove portions other than the stripe region, and p-type InP is again formed on the portion.
A current blocking layer (6) and an n-type InP current blocking layer (7) are formed, and finally a p-type GaInAsP contact layer (8) is formed. In this structure, the active layer (3) is filled with InP layers (6) and (7) having a smaller refractive index than the active layer, so that the transverse mode can be controlled and the current can be confined.
This is realized by utilizing the reverse bias characteristic of the pn junction of the InP layers (6) and (7), and low threshold current is possible.

[Problems of conventional technology]

However, since the mesa etching is performed by the wet etching method, there are the following problems. That is, it is difficult to control the width of the active layer with good reproducibility, and since etching progresses to a specific crystal plane when performing selective etching, unevenness is generated on the side of the mesa and deterioration of crystallinity near the active layer occurs. In addition, when the adhesion between the SiO ₂ film and the semiconductor layer is poor, side etching occurs, which causes a problem when growing the buried layer.

[Means to solve the problem and its action]

The invention was made in light of the above points.
The purpose is to provide a buried semiconductor laser device having a narrow active layer width with good reproducibility and a good buried layer, and the gist thereof is to form a double heterojunction portion including the active layer in a mesa shape. In the method for manufacturing an embedded semiconductor laser device in which the double heterojunction portion is embedded with an embedded layer of a semiconductor having a smaller refractive index than the active layer, the mesa shape is formed by dry etching, and then the dry-etched active layer is formed. A side surface of the layer is selectively wet-etched, and then a preliminary burying layer is embedded on the side surface of the active layer by using a mass transport method such that the active layer etched by the wet etching is restored to its original state. An embedded semiconductor characterized by being embedded in a semiconductor embedded layer having a refractive index smaller than that of the active layer and a high resistance. It is a manufacturing method of over laser device.

With dry etching, the width of the active layer can be accurately controlled. In wet etching, if the etching is isotropic, side etching occurs under the resist film by the same dimension as the depth.
In addition, the selectivity of materials and crystal planes due to chemicals is also high. However, when dry etching is used, the selectivity is lost, and InP and GaInAsP can be etched at a constant rate, and vertical sidewalls without steps at the hetero interface can be obtained. In order to eliminate the influence of ion irradiation damage, which is one of the problems of dry etching, the active layer exposed to plasma is selectively etched by wet etching.

Next, the current blocking layer must be formed by the buried layer. A reverse bias of a pn junction can be used as the current blocking layer, but this method is inferior in high frequency characteristics, so
In the present invention, the buried layer is formed of a high resistance layer of semiconductor.
The high resistance layer of the semiconductor contains impurities, and it is necessary to cover the side surfaces of the active layer in advance by a mass transport method in order to prevent the impurities from adversely affecting the active layer.

〔Example〕

The present invention will be described below based on embodiments shown in the drawings.

FIGS. 1 (a) to 1 (e) are sectional views showing, in order of steps, a main part of an embedded semiconductor laser device manufactured by the manufacturing method according to the present invention.

Next, this manufacturing method will be described in order of steps with reference to the drawings. (1) An n-type InP clad layer (12) and a wavelength of 1.3 μm are formed on the n-type InP substrate (11) by the crystal growth by the MOCVD method of FIG.
GaInAsP active layer (13), p-type I with a composition corresponding to the emission of m
nP clad layer (14), p-type GaInAsP contact layer (15)
Grow continuously. (Fig. 1 (a)) (2) A two-layer resist (photoresist (17)) and a SiO ₂ film (16) pattern with a width of about 1.5 μm were formed by photolithography and reactive ion etching (RIE) with CF ₄ gas. Form. (Fig. 1 (b) (3) n-type InP was used as a two-layer resist mask by reactive ion beam etching (RIBE) using Cl ₂ gas.
Etch to the cladding layer (12). At this time, the wafer is installed so as to have an inclination angle of 21 ° with respect to the ion beam, and etching is performed while rotating the wafer, whereby a substantially vertical etching surface can be obtained. (First
(C)) (4) The uppermost photoresist (17) is removed by ashing the wafer after etching.

(5) Using a mixed solution of 3H ₂ SO ₄ : H ₂ O: H ₂ O ₂ , the active layer (13)
Are selectively etched. (FIG. 1 (d)) (6) After cleaning the wafer, the InP layer is formed on both side surfaces of the selectively etched active layer so as to restore them by the mass transport method using PH ₃ gas. (18) Embed the preliminary embedding layer. Then, using the SiO ₂ film (16) as a mask for selective growth, a high-resistance InP layer (19) containing Fe is grown by the low pressure MOCVD method. At this time, SiO ₂ film (16)
No crystals grow on the mesa stripes. (FIG. 1 (e)) (7) After peeling off the SiO ₂ film, electrodes are formed and cut into chips. The manufacturing method of the embedded semiconductor laser device according to the present invention is not limited to the above-mentioned embodiment, and the RIBE
May be carried out mesa etching by RIEI method instead of the law, instead of the Cl ₂ gas as the etching gas, it may be used after addition of a gas such as Ar Cl ₂ gas and the photoresist / SiO as an etch mask Instead of the combination of _2, the combination of TiO ₂ / SiO ₂ may be used. The emission wavelength of the active layer is not limited to 1.3 μm,
The desired emission wavelength of 1.6 μm can be selected.

〔The invention's effect〕

As described above, according to the present invention, since the mesa shape is formed by dry etching, the width of the active layer can be accurately controlled, and the buried layer is a semiconductor layer having high resistance, which is favorable. There is an excellent effect that high frequency characteristics can be obtained.

[Brief description of drawings]

1 (a) to 1 (e) are cross-sectional views showing the main part of an embedded semiconductor laser device manufactured by the manufacturing method according to the present invention in the order of steps, and FIGS. 2 (a) to 2 (c) are conventional manufacturing processes. FIG. 6 is a diagram showing a cross-section of a main part of an embedded semiconductor laser device by the method in the order of steps. 1,11 …… n-type InP substrate, 2,12 …… n-type InP clad layer, 3,
13 …… GaInAsP active layer, 4,14 …… p-type InP clad layer, 5,
16 …… SiO ₂ film, 6 …… p type InP current blocking layer, 7 …… n type I
nP current blocking layer, 8,15 ... p-type GaInAsP contact layer, 17
...... Photoresist, 18 …… InP pre-filling layer, 19
...... High resistance InP layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-54-154984 (JP, A) JP-A-58-143596 (JP, A) JP-A-60-163489 (JP, A) JP-A-61- 288481 (JP, A) JP 61-147592 (JP, A) JP 62-84581 (JP, A) JP 64-66988 (JP, A)

Claims (2)

[Claims] 1. A method of manufacturing an embedded semiconductor laser device, wherein a double heterojunction portion including an active layer is formed into a mesa shape, and the double heterojunction portion is embedded with a semiconductor burying layer having a refractive index smaller than that of the active layer. The mesa shape is formed by dry etching, then the side surfaces of the dry-etched active layer are selectively wet-etched, and then the mass-transport method is used to restore the active layer etched by the wet-etching to the original state. A method of manufacturing an embedded semiconductor laser device, comprising: burying a preliminary burying layer on a side surface of the active layer, and then burying a semiconductor burying layer having a refractive index smaller than that of the active layer and a high resistance. 2. The burying by the mass transport method and the burying by a burying layer of a semiconductor having a high resistance are performed by a metal organic chemical vapor deposition method.
6. A method for manufacturing an embedded semiconductor laser device according to the item.