JPH05121829A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser which has a first cladding layer, an active layer, a second cladding layer, a third cladding layer and a contact layer which are formed on a substrate and whose third cladding layer has a stripe-shape and whose second cladding layer thickness is accurately controlled to stabilize the operation. CONSTITUTION:In a first type semiconductor laser, compound semiconductor of which the third cladding layer 18 is made has a higher etching speed than compound semiconductor of which the second cladding layer 16 is made. In a second type semiconductor laser, the respective cladding layers 12, 16 and 18 are made of compound semiconductor containing aluminum. The aluminum content in the compound semiconductor of the third cladding layer 18 is higher than the aluminum content in the compound semiconductor of the second cladding layer 16.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to improvements in semiconductor lasers.

[0002]

2. Description of the Related Art In a refractive index guided semiconductor laser,
The active layer is continuous over the entire device, and the transverse mode is confined by providing an effective refractive index difference in the vicinity of the active layer.

A cross-sectional view of such a semiconductor laser is shown in FIG. This semiconductor laser includes a substrate 100, a first
Cladding layer 102, active layer 104, second cladding layer 10
6, a contact layer 110, a stop layer 112, a lower electrode 114, and an upper electrode 116. The upper portion of the second cladding layer 106 has a protruding strip portion 108, and the contact layer 110 is formed on the upper portion 108. This controls the current constriction and the transverse mode.

In order to stably control the transverse mode, it is important to accurately control the effective refractive index difference in the vicinity of the active layer or the injection current distribution. For this, the second
Portion 106A of the cladding layer 106 other than the strip portion 108
It is necessary to make the thickness t of H.sub.2 uniform according to the design value. That is,
Accurate control of the thickness t is essential for stabilizing the operation of the semiconductor laser having the structure shown in FIG. Further, when the thickness t is thicker than about 1 μm, the semiconductor laser becomes a gain waveguide type, but in this case also, the thickness t
It is important to control accurately.

[0005]

Conventionally, in order to manufacture a semiconductor laser having a structure shown in FIG.
The second clad layer 106 and the contact layer 110 are formed. Next, the strip-shaped mask material 130 is applied to the contact layer 11
0 (see FIG. 3B), the contact layer 110 is etched using the mask material as a mask.
Further, a part of the second cladding layer 106 has a thickness t '(= T-
Etch only t). Therefore, the second cladding layer 10
Variations in the thickness T of 6 or variations in etching conditions cause variations in the etching thickness t ′. As a result, the thickness t varies, which causes a problem that the operation of the semiconductor laser becomes unstable.

A semiconductor laser having a structure as shown in FIG. 4 is also known. In such a semiconductor laser, an etching stop layer 120 and a third clad layer 122 are provided between the second clad layer 106 and the contact layer 110. In the etching process, the third cladding layer 122 is etched into the shape shown in FIG. 4, but the etching stopper layer 120 does not etch the second cladding layer 106. The components indicated by other reference numerals in FIG. 4 are the same as those in FIG.

The etching stop layer 120 is made of GaInP or the like having a slow etching rate, but there is a drawback in that the apparatus for growing GaInP or the like has a complicated structure.
In addition, the number of steps for additionally providing the etching stop layer is increased.

Therefore, an object of the present invention is to form a semiconductor in which a first clad layer, an active layer, a second clad layer, a third clad layer and a contact layer are formed on a substrate, and the third clad layer has a stripe shape. (EN) Provided is a laser, in which the thickness of the second cladding layer is accurately controlled and the operation is stable.

[0009]

According to the first aspect of the present invention, the above-mentioned object is that the compound semiconductor forming the third cladding layer has a higher etching rate than the compound semiconductor forming the second cladding layer. It is achieved by a semiconductor laser characterized in that

It is preferable that the compound semiconductor forming the second cladding layer is made of AlGaInP or AlGaInAs, and the compound semiconductor forming the third cladding layer is made of AlGaAs.

Further, according to the second aspect of the present invention, the above object is such that each cladding layer is made of a compound semiconductor containing aluminum, and the aluminum content in the compound semiconductor of the third cladding layer is equal to that of the second cladding layer. Achieved by a semiconductor laser characterized by having a higher aluminum content in the compound semiconductor.

The compound semiconductor of the second cladding layer and the third cladding layer is made of, for example, AlGaAs, and the aluminum content of the compound semiconductor of the third cladding layer is 0.1 than the aluminum content of the compound semiconductor of the second cladding layer.
It is desirable that it is 5 or higher. That is, the composition of the third clad layer is Al _X Ga _1-X As, and the composition of the second clad layer is Al _Y.
When Ga _1-Y As, it is desirable that XY ≧ 0.15.

[0013]

According to the first aspect of the semiconductor laser of the present invention,
The compound semiconductor forming the third clad layer has a higher etching rate than the compound semiconductor forming the second clad layer. Therefore, only the third cladding layer is etched, and the etching stops at the interface between the third cladding layer and the second cladding layer. Therefore, the second clad layer can substantially maintain the thickness as it is formed, and is hardly affected by etching. As a result, the operating characteristics of the semiconductor laser are stabilized and the manufacturing yield of the semiconductor laser is improved.

According to the second aspect of the semiconductor laser of the present invention, the aluminum content in the compound semiconductor of the third cladding layer is higher than the aluminum content in the compound semiconductor of the second cladding layer. Therefore, if an appropriate etching solution is selected, only the third cladding layer is etched, and the etching stops at the interface between the third cladding layer and the second cladding layer. Therefore, the second clad layer can substantially maintain the thickness as it is formed, and is hardly affected by etching. As a result, the operating characteristics of the semiconductor laser are stabilized and the manufacturing yield of the semiconductor laser is improved.

The aluminum content in the AlGaAs layer of the second cladding layer may be set higher than the aluminum content of the AlGaAs layer in the third cladding layer.
If an appropriate etching solution is selected, etching can be stopped at the interface between the third cladding layer and the second cladding layer. However, in this case, the refractive index of the third clad layer is higher than that of the second clad layer, and the vertical light confinement of the semiconductor laser is deteriorated. As a result, the characteristics of the semiconductor laser deteriorate.

[0016]

EXAMPLE 1 A sectional view of a semiconductor laser according to the first aspect of the present invention is shown in FIG. The semiconductor laser is
The lower electrode 24, the substrate 10, the first clad layer 12, the active layer 14, the second clad layer 16, the third clad layer 18, the contact layer 20, the stop layer 22, and the upper electrode 26. These configurations are as follows. Substrate 10: n-GaAs first cladding layer _{12: n-Al 0.4 Ga 0.6} InP active layer 14: undoped GaAs second clad layer _{16: p-Al 0.4 Ga 0.6} InP third clad layer 18: p-Al _0.6 Ga _0.4 As contact layer 20: p + -GaAs

This semiconductor laser can be manufactured by the following method.

[Step A-1] First, MOCVD, MB
The first clad layer 12, the active layer 14, the second clad layer 16, the third clad layer 18, and the contact layer 20 are formed on the substrate 10 by the first crystal growth using E, LPE, or the like.
Are sequentially formed. Here, if necessary, a buffer layer or the like can be provided between the substrate 10 and the first cladding layer 12, or between the third cladding layer 18 and the contact layer 20.

[Step A-2] Next, a mask material such as SiO ₂ is formed on the contact layer 20 by ordinary CVD and patterning steps to form a mask 30 (see FIG. 2A).

[Step A-3] Next, the mask 30
The contact layer 20 and the third cladding layer 18 are etched by using. An etching solution having a higher etching rate for the third cladding layer 18 than that for the second cladding layer 16 is used. As such an etching solution, an etching solution composed of an acid such as sulfuric acid or hydrochloric acid, hydrogen peroxide and water can be used. Such an etchant etches the third cladding layer about 10 times faster than the second cladding layer. The etching stops at the interface between the third cladding layer 18 and the second cladding layer 16 due to the difference in the composition of the compound semiconductors of the second cladding layer 16 and the third cladding layer 18, which is a feature of the present invention ((B) in FIG. reference).

[Step A-4] Next, using SiO ₂ as a mask, a second crystal growth is selectively performed to form a stop layer. It is also possible to smooth the stop layer after performing the second crystal growth without using a mask to form the stop layer. After that, the semiconductor laser is completed by forming the upper electrode and the lower electrode, forming the reflecting surface, pelletizing and the like by a conventional method.

Example 2 Next, a semiconductor laser according to the second aspect of the present invention will be described. The sectional view of this semiconductor laser is similar to that of FIG. The structure of such a semiconductor laser is as follows. Substrate 10: n-GaAs first cladding layer _{12: n-Al 0.45 Ga 0.55} As active layer 14: undoped GaAs second clad layer _{16: p-Al 0.45 Ga 0.55} As third cladding layer 18: p-Al _0.70 Ga _0.30 As contact layer 20: p + -GaAs

This semiconductor laser can be manufactured by the following method. During the manufacturing process, [Process B-1] and [Process B-2] are the same as [Process A-1] and [Process A-2] of Example-1, and the description thereof will be omitted.

[Step B-3] Following the step B-2, the contact layer 20 and the third cladding layer 18 are etched using the mask material as a mask. An etching solution having a higher etching rate for the third clad layer than that for the second clad layer is used. An HF-based etching solution can be used as the etching solution. The HF-based etchant etches the third cladding layer about 10 times faster than the second cladding layer. AlG of the second clad layer and the third clad layer, which is a feature of the present invention
Due to the difference in the aluminum content in aAs, etching stops at the interface between the third cladding layer and the second cladding layer.

The subsequent [Step B-4] is the same as [Step A-4] and the description thereof is omitted.

Although the present invention has been described above based on the preferred embodiments, the present invention is not limited to these embodiments.

For example, AlGaInAs can be used as a compound semiconductor forming the first cladding layer and the second cladding layer of the semiconductor laser according to the first aspect of the present invention.

For example, AlGaInP is used as a compound semiconductor forming the first cladding layer, the second cladding layer and the third cladding layer of the semiconductor laser according to the second aspect of the present invention.
And AlGaInAs can be used. The aluminum content of the compound semiconductor depends on the combination with the etching solution as long as etching stops at the interface between the third clad layer and the second clad layer, but an appropriate content can be selected.

The semiconductor laser of the present invention can be applied to a twin stripe type semiconductor laser.

[0030]

According to the semiconductor laser of the present invention, if the proper etching solution is selected, only the third cladding layer is etched, and the etching stops at the interface between the third cladding layer and the second cladding layer. Therefore, the thickness of the second clad layer can be almost maintained as it is, and the thickness of the second clad layer can be accurately controlled without being affected by etching. As a result, not only the operating characteristics of the semiconductor laser are stabilized, but also the manufacturing yield of the semiconductor laser is improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor laser of the present invention.

FIG. 2 is a cross-sectional view of a semiconductor laser for showing a manufacturing process of the semiconductor laser of the present invention.

FIG. 3 is a sectional view showing an example of a conventional index-guided semiconductor laser.

FIG. 4 is a sectional view showing another example of a conventional index-guided semiconductor laser.

[Explanation of symbols]

 10 substrate 12 first clad layer 14 active layer 14 16 second clad layer 18 third clad layer 20 contact layer 22 stop layer 24 lower electrode 26 upper electrode

Claims (2)

[Claims] 1. A semiconductor laser comprising a first clad layer, an active layer, a second clad layer, a third clad layer and a contact layer formed on a substrate, wherein the third clad layer has a stripe shape. A semiconductor laser, wherein the compound semiconductor forming the 3 clad layer has a higher etching rate than the compound semiconductor forming the second clad layer. 2. A first clad layer, an active layer, a second clad layer, a third clad layer and a contact layer are formed on a substrate, each clad layer being made of a compound semiconductor containing aluminum, and the third clad layer. Is a stripe-shaped semiconductor laser, wherein the aluminum content in the compound semiconductor of the third cladding layer is higher than the aluminum content in the compound semiconductor of the second cladding layer.