JPH067622B2 - Method for manufacturing semiconductor laser device - Google Patents

Description

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

Structure of conventional example and its problems Chemical etching of compound semiconductors of GaAs or GaAlAs system has been studied for a long time, and there are many reports on its etching characteristics. Etchant, etching rate, Ga
The details of As or GaAlAs selective etching solutions and etching profiles are known. Using such chemical etching technology, GaAs surface treatment and GaAs
/ GaAlAs wafers have been selectively etched. Further, such a technique has also been used for producing a cavity surface of a semiconductor laser or the like.

A semiconductor laser generally has a cavity surface formed by a cleavage method. However, when a semiconductor laser and an element such as a detector or a driving circuit are to be monolithically integrated like an optical IC, the cleavage method should not be used at all. Can not. Therefore, a wet etching method using a chemical etching method and a dry etching method such as a reactive ion etching (RIE) have been studied. The chemical etching method is excellent in terms of mass production and reliability, and due to its ease, attempts have been made to produce a cavity surface by various methods. The problems in the production of the cavity surface by the chemical etching method are the verticality of the cavity surface and the flatness of the surface.

1A and 1B show the relationship between the inclination θ of the cavity surface and the normalized reflectance. As can be seen from the figure, the reflectance decreases by 50% only by tilting the cavity surface by about 5 °, which leads to an increase in the threshold value and a decrease in the external differential quantum efficiency. Further, the reflectance is significantly lowered due to the roughness of the surface of the cavity surface. Due to such a problem, the laser manufactured by the conventional chemical etching method has a higher threshold current density than that of the cleavage method, and continuous oscillation is extremely difficult.

SUMMARY OF THE INVENTION In view of the above drawbacks, the present invention provides a method of manufacturing a semiconductor laser device in which a vertical and flat cavity surface is formed by an etching method.

To achieve this object, in the method for manufacturing a semiconductor laser device of the present invention, after removing a part of the cap layer, a mask having an open end in the <011> direction is formed on the cladding layer. , Forming a cavity surface by etching through the openings.

Description of Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 2 shows the experimental results on the tilt angle of the etching profile when a Ga _1-x Al _x As layer was grown on a (100) GaAs substrate and etched through a stripe-shaped mask along the <011> direction. Shows. The tilt angles θ ₁ and θ ₂ largely change depending on the AlAs mixed crystal ratio x. When the value of x is near 0.2 and near 0.4, the tilt angle θ
₁ becomes about 90 °. On the other hand, the angle θ ₂ generated at the interface with the GaAs substrate is almost 0 at x <0.1 and x to 0.4.
Has become. Focusing on x near 0.4, θ ₁ ~
At 90 °, θ _{2 to} 0 ° C., and the etching end surface becomes a vertical and flat surface. If this result is applied to a semiconductor laser, a cavity surface almost equivalent to the cleavage surface can be obtained.

As one of the examples, a method for producing the AlAs mixed crystal ratio of the clad is set to 0.4 from the result shown in FIG.

As shown in FIG. 3 (a), an n-type Ga _0.6 Al _0.4 As clad layer 2, a GaAs active layer 3 and a p-type are formed on an n-type GaAs (100) substrate 1.
Ga _0.6 Al _0.4 As clad layer 4 and p-type GaAs cap layer 5
To grow continuously.

After that, a stripe-shaped photomask 6 is formed along the <011> direction, and only the GaAs cap layer 5 is selectively etched through the mask (FIG. 3 (b)).

Further, after removing the resist 6, the exposed p-type Ga _0.6 Al
_0.4 As Striped photomask 6 on clad layer 4
Are formed along the <011> direction, and the substrate is etched through this mask (FIG. 3 (c)). Incidentally, the etchant used is _{1H 2 SO 4: 8H 2 O} 2: 1H 2 O (20
℃).

When the etching is performed by the above method, an end face which becomes a cavity face is obtained as a mirror face which is perpendicular to the pn junction face and is extremely flat. By the way, in the wafer of FIG. 3 (a), p-type GaA
When etching is performed from above the s cap layer 5 through a photomask, an etching profile having an inverted mesa shape is shown as shown in FIG. 4, and the cavity surface of the semiconductor laser becomes extremely low.

After forming the positive electrode 7 on the cap layer of the wafer obtained in FIGS. 3 (a) to 3 (c) and the negative electrode 8 on the substrate side, the substrate is broken at the etched groove to form the fifth electrode. A semiconductor laser device is obtained as shown in the figure.

The optical output-current characteristics of the semiconductor laser device of FIG. 5 are shown in FIG. It is obtained with continuous oscillation at a very high yield, and the typical oscillation threshold is 72 mA (70 mA in the cleavage method).
The differential quantum efficiency is 29% per side (30 in the cleavage method).
%) And a characteristic that is almost the same as the cleavage method was obtained.

EFFECTS OF THE INVENTION A feature of the present invention is that a cavity surface which is perpendicular to the joint surface and which is a mirror surface can be produced by a chemical etching method. The advantage of obtaining a cavity surface equivalent to the cleavage surface by the chemical etching method is that other elements can be easily integrated on the same substrate, a short cavity laser can be manufactured, and a protective film for the laser end surface is formed by batch processing. What can be done and that the inspection of the characteristics can be done with the wafer as it is, and the practical effect is great.

[Brief description of drawings]

1 (a) and 1 (b) show the relationship between the tilt of the cavity surface and the reflectance, and FIG. 2 shows Ga _1-x Al _x As on a (100) GaAs substrate.
FIG. 3 (a), FIG. 3 (b), and FIG. 3 (c) are views showing the inclination of the etching end face when a layer is grown and etching is performed through a stripe-shaped mask along the <011> direction. Showing a method for manufacturing a cavity surface by etching of FIG. 4, FIG. 4 is a view showing an etching profile of a wafer by conventional etching, FIG. 5 is a perspective view of a semiconductor laser manufactured by the manufacturing method of the present invention, and FIG.
The figure shows the optical output-current characteristics of the same semiconductor laser. 1 ... n-type GaAs (100) substrate, 2 ... n-type Ga _0.6 Al _0.4
As clad layer, 3 ... GaAs active layer, 4 ... p-type Ga _0.6 Al
_0.4 As clad layer, 5 ... p-type GaAs cap layer, 6 ...
Photomask, 7 ... Positive electrode, 8 ... Negative electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yuichi Shimizu, 1006 Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. (72) Takashi Sugino, 1006, Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] _1. A Ga _1-x Al having an active layer and a mixed crystal ratio x sandwiching the active layer on a (100) GaAs substrate with 0.15 ≦ x ≦ 0.25 or 0.35 ≦ x ≦ 0.45. _x As clad layer, a cap layer is further formed on the clad layer, a part of the cap layer is removed to expose the surface of the clad layer, and A mask having stripe-shaped openings along the 011> direction is formed, and a vertical and flat cavity surface is formed by etching the GaAs substrate through the openings with an etching solution containing sulfuric acid, hydrogen peroxide solution and water. A method of manufacturing a semiconductor laser device, comprising: