JPS63318192A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To make only the region of both the ends of an active layer melt back so as to improve a yield by a method wherein a mesa section with only the active layer protruding outward at both sides is formed through the selective etching. CONSTITUTION:After an active layer 12 and a clad layer 3 are formed on a substrate 1, a mask 4 is formed and then a mesa section is built through etching and moreover formed into such a mesa shape as only both the ends 7 of the active layer 2 protrude outward through an etching solution which is slow in etching speed against the active layer 3. The mask 4 being removed, a first current block layer 5 and a second current block layer 6 are formed through the liquid growth using a melt supersaturated or non-saturated to a slight degree. Then, only the protrusions 7 are melted back during the liquid phase growth being performed. The both ends 7, which are deteriorated due to being exposed to the external atmosphere, can be stably removed, so that the semiconductor laser with a long life can be manufactured with an excellent yield.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a semiconductor laser, which can produce a semiconductor laser with a low threshold value and a long life with a high yield.

[Conventional technology]

FIG. 2 is a sectional view showing the structure of a conventional buried semiconductor laser disclosed in, for example, Japanese Patent Application Laid-Open No. 13588/1983.

In this figure, 1 is a substrate of the first conductivity type, and 2 is an active layer, which is formed into a rectangular shape in order to efficiently confine injected current and light therein. 3 is a cladding layer of the second conductivity type, 5 is a first current blocking layer of the second conductivity type, and 6 is a second current blocking layer of the first conductivity type.

Next, the operation will be explained.

When a voltage is applied across the substrate 1 and the cladding layer 3, electrons and holes are injected into the active layer 2, causing radiative recombination, and when the injection reaches a certain level, laser oscillation occurs. At this time, the carriers are constricted by the reverse junction formed between the second current blocking layer 6 and the first current blocking layer 5, and efficiently concentrate and flow into the active layer 2. For this reason, semiconductor lasers operate with low reactive current and high efficiency.

In addition, in the manufacturing process, in order to make the active layer 2 rectangular, the active layer 2 is first grown on the substrate 1 in the first crystal growth.
After sequentially growing the cladding layer 3 over the entire surface, etching is performed from the cladding layer 3 to the substrate 1 using photolithography to form a mesa portion, and the second crystal growth is performed on the substrate 1 on both sides of the mesa portion. 1st on top. Second current blocking layer 5.6
are gradually growing.

However, in such a manufacturing method, the crystal deteriorates due to exposure to outside air in the region of the active layer 2 in contact with the second current blocking layer 6 from after the formation of the mesa portion until the start of the second crystal growth. . That is, non-radiative recombination occurs in the regions where the crystals at both ends of the active layer 2 have deteriorated, leading to an increase in the laser oscillation threshold current and a decrease in the light emission efficiency, thereby shortening the operating life.

Therefore, as a countermeasure to this problem, conventionally, in the second crystal growth stage, prior to the growth of the first current blocking layer 5, an unsaturated melt is used to degrade the crystals at both ends of the active layer 2. The method used is to melt back the area.

[Problem that the invention seeks to solve]

In the conventional method for manufacturing a semiconductor laser as described above, the regions where the crystals at both ends of the active layer 2 have deteriorated are removed by meltback, but it is very difficult to control this, and it is difficult to remove not only the regions at both ends of the active layer 2 but also the regions where the crystal has deteriorated. Since the active layer 2 and the cladding layer 3 are melted back more than necessary, there is a problem in that the yield is low.

The present invention has been made to solve these problems, and is a semiconductor laser that can stably melt back only the regions at both ends of the active layer and provide a high-yield, high-performance buried semiconductor laser. The purpose is to obtain a manufacturing method.

[Means for solving problems]

A method for manufacturing a semiconductor laser according to the present invention includes a step of sequentially forming an active layer and a cladding layer of a second conductivity type on a semiconductor substrate of a first conductivity type, and etching using selectivity from the cladding layer to the semiconductor substrate. forming a mesa portion in which only the active layer protrudes from both ends; and applying a first current of a second conductivity type to the semiconductor substrate on both sides of the mesa portion using a melt having a small degree of supersaturation or non-saturation. block layer and first
The method includes a step of forming a conductive type second current blocking layer.

[Effect]

In this invention, 1. During crystal growth of the second current blocking layer, only the regions at both ends of the active layer protruding from the mesa portion are melted back.

(Embodiment) FIGS. 1(a) to 1(d) are cross-sectional views for explaining an embodiment of the method for manufacturing a semiconductor laser of the present invention.

In these figures, the same reference numerals as in FIG. 2 indicate the same parts, 4 is an etching mask, 7 is a region at both ends of the active layer 2, and 7a is a region disappeared due to meltback.

Next, the manufacturing process will be explained.

First, as shown in FIG. 1(a), an active layer 2 and a cladding layer 3 are sequentially grown on a substrate 1 in the first crystal growth. Next, as shown in FIG. 1(b), after forming an etching mask 4 on the cladding layer 3 using photolithography, etching is performed from the cladding layer 3 to the substrate 1 using this etching mask 4. to form a mesa part.

At this time, an etching solution with low selectivity is used as the etching solution. Next, as shown in FIG. 1C, a mesa portion in which only the active layer 2 protrudes from both ends is formed using an etching solution that etches the substrate 1 and cladding layer 3 at a higher etching rate than the active layer 2. do.

After that, after removing the etching mask 4, the etching mask 4 is removed.
), a first current blocking layer 5 and a second current blocking layer 6 are formed on the substrate 1 on both sides of the mesa by performing the second crystal growth using a melt with a small degree of supersaturation or nonsaturation. are formed sequentially. At this time, only the regions 7 at both ends of the active layer 2 are melted back due to the characteristic of liquid phase growth that "the protrusions are more likely to be melted back than other parts even if a supersaturated melt is used."

That is, in this embodiment, the regions 7 at both ends of the active layer 2 that have been exposed to the outside air and have deteriorated are removed by meltback, so that almost no non-radiative recombination occurs.

In the above embodiment, the case where wet etching was used was explained, but dry etching may also be used.

In addition, in the above embodiment, etching with low selectivity and etching with high selectivity are performed in two stages to form the active layer 2.
Although a case has been described in which a mesa portion is formed with only a single protruding portion at both ends, it is also possible to form the mesa portion described above by one-time etching using an etching liquid having medium selectivity.

〔Effect of the invention〕

As explained above, this invention includes a step of sequentially forming an active layer and a cladding layer of a second conductivity type on a semiconductor substrate of a first conductivity type, and etching using selectivity from the cladding layer to the semiconductor substrate. A step of forming a mesa portion in which only the active layer protrudes from both ends, and a step of forming a second mesa portion on the semiconductor substrate on both sides of this mesa portion using a melt with a small degree of supersaturation or unsaturation.
A 175th block layer of conductivity type and a second block layer of first conductivity type.
Since the step of sequentially forming current blocking layers can reduce defects that are formed by oxidation and cause non-radiative recombination during operation, it is possible to create a semiconductor laser that operates with a low threshold value, low operating current, and has a long life. It has the effect of being able to be obtained at a high yield.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view for explaining an embodiment of the semiconductor laser manufacturing method of the present invention, and FIG. 2 is a cross-sectional view showing the structure of a conventional buried semiconductor laser. In the figure, 1 is a substrate, 2 is an active layer, 3 is a cladding layer,
4 is an etching mask, 5 is a first current blocking layer, and 6 is a second current blocking layer. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Masuo Oiwa (2 others) Figure 1 (a) Figure 1 (d) Figure 2 procedural amendment (voluntary) 1. Display of the incident Patent Application No. 154106/1982 2.
Title of invention: Method for manufacturing a semiconductor device; 3. Representative of the person making the amendment Moriya Shiki 4, Agent 5, Brief description of drawings in the specification to be amended and Drawing 6, Contents of the amendment (1) “6” on page 8, line 14 of the specification is the second current blocking layer.'' is corrected as follows. [6 is the second current blocking layer, 7 is the region at both ends of the active layer,
7u is an area that disappeared due to meltback. (2) In the drawings, Figure 1 should be amended as shown in the attached sheet. Figure 1 (a) l Diagram of both ends of the active layer Figure 1

Claims (1)

[Claims] A process of sequentially forming an active layer and a cladding layer of a second conductivity type on a semiconductor substrate of a first conductivity type, and selectively etching from this cladding layer to the semiconductor substrate so that only the active layer is etched at both ends. A step of forming a protruding mesa portion, and forming a first current blocking layer of a second conductivity type and a second current blocking layer of the first conductivity type using a melt having a small degree of supersaturation or non-saturation on the semiconductor substrate on both sides of the mesa portion. 1. A method of manufacturing a semiconductor laser, comprising the step of sequentially forming current blocking layers.