JPS6349918B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention has a current blocking layer (100)
A stripe groove is formed in the [011] direction of a plane InP substrate, and an InP cladding layer of the first conductivity type is formed on the substrate.
InGaAsP active layer, second conductivity type InP cladding layer,
This invention relates to a semiconductor laser having a structure in which a crescent-shaped active layer is buried in a groove by sequentially epitaxially growing a second conductivity type InGaAsP contact layer.

Conventionally, the manufacturing method for this type of semiconductor laser is as follows:
There is a method of manufacturing a semiconductor laser having the structure shown in FIG. 1b or 2b using a substrate having a groove having a cross-sectional shape shown in FIG. 1a or 2a.

To manufacture the semiconductor laser shown in FIG. 1b,
First, InGaAsP layer 2, InP layer 3, and
An InGaAsP layer 4 is formed. Note that the InP layer 3 is a current blocking layer that functions to prevent current from leaking to areas other than the active layer when a semiconductor laser is manufactured.
Its thickness is about 1 to 3 μm. next,
InP layer 3 was etched using concentrated hydrochloric acid using InGaAsP layer 4 as an etching mask (mask width: 1.5 to 2 μm) [011]
Stripe grooves are etched in the direction of the pattern. At this time, the InP layer 3 is etched much faster in the depth direction than in the width direction.
Due to the presence of the InGaAsP layer 2, a groove 5 having a dovetail cross-sectional shape is formed as shown in FIG. 1a. In this case, since the InGaAsP layer 4 is not easily immersed in the hydrochloric acid-based etching solution, there is almost no side etching and a groove with a narrow width of about 2 μm can be formed. After that, this dovetail groove 5
Using a substrate with n-InP cladding layer 6,
InGaAsP active layer 7, p-InP cladding layer 8, p-
By epitaxially growing the InGaAsP contact layer 9 in sequence, a semiconductor laser having a structure in which the crescent-shaped active layer 7 is buried in the groove 5 of the substrate as shown in FIG. 1B can be manufactured. In addition, in FIG. 1b, the groove 5 that existed when forming the groove 5 on the substrate
A case is shown in which parts of the InGaAsP layer 2 and the InGaAsP layer 4 are melted back and disappear during the next crystal growth. However, in the semiconductor laser configured in this manner, the side surface 10 of the dovetail groove 5 is not a plane indicated by the plane index of the crystal, so when the side surface of the groove 5 is observed along the [011] direction, it is uneven. , and since the crystal is grown using a substrate having grooves 5 with these unevenness, the end portion of the crescent-shaped active layer 7 is [011]
The active layer 7 has a uneven distribution in the direction, and the width of the active layer 7 has a distribution in the [011] direction, making it difficult to obtain a smooth far-field image.

In order to manufacture the semiconductor laser shown in FIG. 2b, first, a wafer having a p-InP layer 11 formed on the n-InP substrate 1 which functions as a current blocking layer is coated with a silicon oxide (SiO ₂ ) film. A V-shaped groove 12 is created by etching the silicon oxide film, which is the mask, with a hydrochloric acid-based etching solution (3HCl:H ₃ PO ₄ ) to create an undercut using a mask. Using a substrate having grooves 12, an n-InP cladding layer 6, an InGaAsP active layer 7, and a P
The -InP cladding layer 8 and the p-InGaAsP contact layer 9 are epitaxially grown in sequence, and the crescent-shaped active layer 7 is buried in the groove 12 of the substrate.

However, in the semiconductor laser configured in this way, the side surfaces of the V-shaped groove 12 are (111) of the crystal.
Although the B-side is exposed and a smooth surface is obtained, the V-shaped groove 12 is formed due to strong side etching of the silicon oxide film used as an etching mask, and it is difficult to narrow the width of the groove 12. Therefore, it is difficult to narrow the width of the crescent-shaped active layer 7, and there is a drawback that the active layer thickness conditions for oscillation in the transverse fundamental mode become strict. In other words, the conditions for higher-order mode oscillation are determined by the relationship between the width and thickness of the active layer 7, and the active layer thickness is set to 0.1 to 0.15 μm.
This is because when the active layer grows to a certain extent, the width of the active layer must be suppressed to about 2 μm in order to stably perform fundamental lateral oscillation.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and the current blocking layer has an exposed (111) B plane, which is a smooth crystal plane, on the lower part, and a current blocking layer on the upper part. By forming a groove with a narrow and restricted structure in the current blocking layer and providing a crescent-shaped active layer within this groove, it is possible to obtain a smooth far-field pattern and a margin for the conditions for transverse fundamental oscillation. The purpose of this invention is to provide a semiconductor laser that can be used.

An embodiment of this invention is shown below in Figures 3 and 4.
To explain based on the figure, the same reference numerals as those shown in FIG. (111) B side 14
A striped groove with a narrow width at the top and a crescent shape in cross section where the end part touches the boundary between the area where the (111) B plane appears in the groove and the area where the groove width is restricted. An InGaAsP active layer 7 having a shape is formed therein.

Next, a method for manufacturing the semiconductor laser shown in FIG. 3 will be described. First, similarly to the method shown in FIG. After epitaxially growing layer 3 and InGaAsP layer 4,
InGaAsP layer 4 is masked (mask width is 1.5 to 2μ)
As m), InP layer 3 was etched with concentrated hydrochloric acid.
The cross-sectional shape shown in FIG. 4 in the [011] direction of the InP layer 3,
In other words, a striped groove 13 having a lower part where the smooth (111)B plane of the InP layer 3 is exposed and an upper part having a narrow and limited width is formed. This groove 13 has a smooth InP layer 3 (111)B at the bottom.
The surface is exposed and can be used as an etching mask.
Since the InGaAsP layer 4 is used, there is almost no side etching and the groove width can be narrowed.
When etching to form the groove 13, as the etching time becomes longer, the (111)B plane of the InP layer 3 exposed at the bottom is also etched, and the shape of the groove approaches the shape shown in FIG. Therefore, the bottom has the (111)B plane of InP layer 3, and the bottom edge is
The etching time is set so that the etching ends when the InGaAsP layer 2 is reached.

After forming a substrate having grooves 13 as shown in FIG. 4 in this way, the n-InP cladding layer 6,
The InGaAsP active layer 7, the p-InP cladding layer 8, and the p-InGaAsP contact layer 9 are epitaxially grown in sequence, and the (111) layer of the InP layer 3 is grown in the groove 13.
It is possible to fabricate a semiconductor laser having the structure shown in FIG. 3, which has a crescent-shaped active layer 7 whose end portion touches near the boundary between the area where the B plane is exposed and the area where the groove width is restricted. .

In a semiconductor laser manufactured in this way, in order to reduce leakage current, it is necessary to grow the active layer 7 within a certain range of the current blocking layer 3 (if it has a multilayer structure). 7
The position of n-InP is determined by the thickness of the n-InP cladding layer 6 grown before the active layer.
Although it is necessary to control the layer thickness of the InP cladding layer 6, the growth rate of the n-InP cladding layer 6 (here, it means the speed at which the growth layer thickness increases over time) depends on the relationship with the area, etc. , the range where the (111)B plane of the InP layer 3 forming the lower part of the groove 13 is exposed (range below the broken line A shown in FIG. 4)
The groove width forming the upper part of the groove 13 is different in the restricted range (range above the broken line A shown in FIG. 4), and the growth rate in the latter is slower than that in the former, so the active layer 7 can be easily controlled near the boundary 15 between the former and the latter, and the smooth crystal plane ((111)B of InP layer 3
It is possible to produce a narrow active layer 7 at a position where the surface of the active layer 7 is exposed.

Therefore, for this semiconductor laser,
The active layer 7 is grown in the (111) B plane of the InP layer 3 where the smooth crystal plane is exposed, and the active layer 7 has little or almost no unevenness distribution at the end portion in the [011] direction. Since the width of the active layer is narrow, it has a smooth far-field pattern and stable transverse fundamental oscillation, and can be manufactured under flexible conditions. It is something.

In addition, in the above embodiment, the lower end of the groove 13
The case where InGaAsP layer 2 exists is shown, but this
It is also possible to omit the InGaAsP layer 2, in which case the groove 13 will have an arrowhead shape as shown in FIG. 5, but the same effect can be obtained.

Also, instead of the InGaAsP layer 4 used as an etching mask for forming the groove 13 in FIG.
A similar effect can be obtained when using a substrate in which grooves 13 as shown in FIG. 6 are formed using a film with almost no side etching as a mask for the etching process.

As described above, this invention has a stripe groove in the [011] direction of the current blocking layer, the lower part of which has a surface where the (111) B plane of the current blocking layer is exposed, and the upper part of which has a striped groove whose width is narrowly limited. is formed, and an active layer having a crescent-shaped cross section is formed within this groove, which has the effect of providing a smooth far-field pattern and stable transverse fundamental mode oscillation.
Furthermore, during fabrication, it is possible to provide a margin for the conditions for oscillation in the transverse fundamental position.

[Brief explanation of the drawing]

Figures 1a and 2b and 2a and 2b respectively show conventional semiconductor laser manufacturing methods.
Figures a and 2a are cross-sectional views of the grooved substrate used, Figures 1b and 2b are cross-sectional views of the fabricated semiconductor laser, respectively, and Figures 3 and 4 are sectional views of the grooved substrate used.
The figures show one embodiment of the present invention, FIG. 3 is a sectional view, FIG. 4 is a sectional view of a grooved substrate used in the one shown in FIG. 3, and FIGS. FIG. 3 is a cross-sectional view of a grooved substrate showing an example of the present invention. In the figure, 1 is an n-InP substrate, 2 is InGaAsP
layer, 3 is current blocking layer, 4 is InGaAsP layer, 6
is the n-InP cladding layer, 7 is the InGaAsP active layer, and 8 is the n-InP cladding layer.
9 is a p-InP cladding layer, 9 is a p-InGaAsP contact layer, 13 is a stripe groove, and 14 is a [111]B plane of the InP crystal. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Formed in the [011] direction of the current blocking layer,
A semiconductor laser having a stripe groove whose lower part has an exposed (111) B plane of a current blocking layer and whose upper part has a narrowly restricted width, and an active layer formed in this stripe groove and having a crescent-shaped cross section. .