JPH0116035B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing an AlGaAs/GaAs semiconductor laser that oscillates in a fundamental transverse mode with a low threshold current.

(Prior Art) Various structures of this type of AlGaAs/GaAs semiconductor laser have been proposed. Literature: "Report of the Institute of Electrical Communication Engineers", ED81-42, (1981), p31~
39 discloses a semiconductor laser device with a V-groove as an example. FIGS. 3A and 3B are process diagrams for explaining the manufacturing method.

First, the (100) plane 10a of the p-GaAs substrate 10
After crystal-growing the n-GaAs layer 11 on top, SiO ₂
Apply a suitable etching mask such as
A groove 1 with a V-shaped cross section and a stripe direction in the <011> direction is formed using a normal photolithography method.
2 to obtain a wafer structure as shown in the perspective view of FIG. 3A. This V-groove 12 allows n-GaAs
Layer 11 is separated into two parts 11a and 11b, each serving as a current confinement layer.

Next, p-
A lower cladding layer 13 of AlGaAs, an active layer 14 of AlGaAs, an upper cladding layer 15 of n-AlGaAs,
A cap layer 16 of n-GaAs is grown by continuous liquid phase epitaxial growth to obtain a wafer structure as shown in the cross-sectional view of FIG. 3B.

According to this structure, when a voltage is applied so that the cap layer 16 side is the negative electrode and the substrate 10 side is the positive electrode, the current confinement layers 11a and 1 outside the V-groove 12 are
1b and the lower cladding layer 13 is reverse biased, the active layer 14 at the top of the V-groove 12
oscillation region 17 (shown with diagonal lines in FIG. 3B)
The injection current is efficiently injected into the oscillator, and therefore oscillates at a low threshold current.

In addition, the n-GaAs current confinement layers 11a and 11
b also acts as a light absorption layer. Therefore, if the film thickness of the p-AlGaAs lower cladding layer 13 on the current confinement layers 11a and 11b is set to be as thin as about 0.3 μm, the wave will oscillate from the oscillation region 17 and be guided outside the V-groove 12. The light is not confined in this part,
Absorbed by the lower light absorbing layer. Therefore, an effective refractive index difference is created between the oscillation region 17 and the region of the active layer 14 outside this region, and therefore, it is possible to oscillate in a stable transverse fundamental mode.

Considering the above points, when manufacturing a semiconductor laser with this conventional structure, it is necessary to grow crystals of the lower cladding layer 13 outside the V-groove 12 in a well-controlled manner to a thickness of about 0.3 μm, and to grow the AlGaAs active layer 14 in a well-controlled manner. It is necessary to grow crystals to a uniform thickness, for example, 0.05 to 0.10 μm, over the entire substrate.

(Problems to be Solved by the Invention) However, in the conventional manufacturing method as described above, a lower cladding layer of p-AlGaAs is grown by liquid phase epitaxial growth on a wafer with a V-groove.
There is a difference in growth rate between the inside and outside of the V-groove,
For this reason, it was technically difficult to control the film thickness outside the groove to about 0.3 μm and grow an AlGaAs active layer with a uniform thickness above it.

An object of the present invention is to create a semiconductor laser that can grow the lower cladding layer and the active layer while controlling their film thickness without losing the conventional low threshold and stable transverse fundamental mode oscillation characteristics. The purpose of this invention is to provide a method for manufacturing the same.

(Means for Solving the Problems) In order to achieve this objective, according to the present invention, first, a
The first layer for the lower cladding layer, the active layer and the upper cladding layer respectively made of AlGaAs, and for current confinement.
GaAs layers are grown sequentially.

Next, first and second grooves having a dovetail cross-sectional shape (these grooves are also referred to as double dovetail grooves) are formed in the GaAs layer for current confinement so that they form stripes in the <011> direction and both grooves. are formed so that they are parallel to each other.

Next, on this grooved GaAs layer, make sure that the GaAs layer is exposed between these two grooves.
Grow an anti-meltback layer of AlGaAs.

Next, in the second crystal growth, meltback is performed using the difference in solubility between the AlGaAs layer and the GaAs layer in the GaAs solution, and the gap between the two grooves is
The GaAs layer region is removed down to the first cladding layer to form a third trench.

A second layer for the upper cladding layer is then grown within the third groove and on the anti-melt back layer.

Thereafter, each required component is formed to obtain a semiconductor laser.

In this case, the GaAs layer and the anti-melt back layer separated by the third groove form a current confinement layer.

(Function) As described above, according to the present invention, the lower cladding layer, the active layer, and the first layer for the upper cladding layer are grown on a flat substrate surface, so that the film thickness of these layers can be grown with good control. Therefore,
The thickness of the first layer for the upper cladding layer can be controlled to a thickness of about 0.3 μm, and the thickness of the active layer can be controlled to a thickness of 0.05 to 0.10 μm with good reproducibility. Furthermore, double dovetail grooves (first and second grooves) are etched in the GaAs layer for the current confinement layer, and an AlGaAs anti-meltback layer is grown on the grooved GaAs layer. This anti-melt back layer can be prevented from growing on the mesa-type GaAs portion between the second groove and the second groove, and therefore,
GaAs meltback can be performed with good reproducibility.

(Example) Hereinafter, with reference to the drawings, AlGaAs/
A method for manufacturing a GaAs-based semiconductor laser device will be explained. 1A to 1D are manufacturing process diagrams for explaining the method of manufacturing a semiconductor laser of the present invention, and FIG. 2 is an explanatory diagram of a double dovetail type groove used in the present invention. Each figure schematically shows the state of the wafer structure at the main manufacturing stage of this process.

First, in the step shown in the perspective view of FIG. 1A,
A p-GaAs substrate 20 with (100) plane orientation is prepared,
On the flat substrate surface 20a of this substrate 20, p-
AlGaAs lower cladding layer 21, AlGaAs active layer 22, n-AlGaAs upper cladding first layer 2
3. Serves as a light absorption layer and also serves as a current confinement layer.
GaAs layers 24 are sequentially grown by liquid phase epitaxial growth to obtain a wafer structure as shown.

Next, the GaAs layer 24 is formed with a stripe direction in the <011> direction by a normal photolithography etching method. First and second grooves 25 and 26 having a dovetail cross-sectional shape are formed in parallel and at a depth up to the middle of the thickness of the GaAs layer 24 (these grooves 25 and 26 are referred to as double dovetail grooves), A wafer structure as shown in the perspective view of FIG. 1B is obtained.

In this case, as shown in a partially enlarged view in FIG. 2, the groove width w ₁ of the first and second grooves 25 and 26 and the width w 2 of the mesa-type GaAs layer region ₂₇ between these grooves 25 and 26. On these grooved GaAs layers 24, an anti-melt back layer, which will be described later, is formed.
The ratio relationship is set so that the anti-melt back layer does not grow on the surface of the mesa region 27 when AlGaAs is grown. In this example,
The groove width w ₁ is 5 to 10 μm, and the width w ₂ of the mesa-shaped region 27 is
is 4 μm. In this case, the depth of the groove does not have much influence on the growth of the anti-melt back layer, but the deeper the groove, the better.

Next, the entire surface of this grooved GaAs layer 24 is covered with p-
An anti-melt back layer 28 of AlGaAs is grown. In this case, in order to cause the growth layer 28 to have an anti-meltback effect against an unsaturated GaAs solution, which will be described later, AlGaAs is used with an Al composition ratio of 0.3 mole fraction or more. In this case, the AlGaAs solution sufficiently contacts the surfaces 24a and 24b of the GaAs layer 24 outside the two grooves 25 and 26, the bottom surfaces 25a and 26a and the side surfaces 25b and 26b inside the grooves 25 and 26, and starts growing. (Figure 2). but,
This growth is faster at the bottom and sides of grooves 25 and 26 because more solute flows into grooves 25 and 27. On the other hand, when the width w ₂ is narrower than the groove width w ₁ ,
There is no solute on the surface 27a of the mesa-type GaAs layer region 27, so AlGaAs does not grow at all.

Therefore, through this AlGaAs growth process, a wafer having a structure as shown in the cross-sectional view of FIG. 1C is obtained.

Note that although the groove in the GaAs layer 24 is a double dovetail type groove, other grooves such as a mesa type can be used.
If both sides of the GaAs layer region 27 are removed and the flat surfaces are formed, there are only two sides of the GaAs layer region 27 where AlGaAs grows quickly, and therefore the surface of the mesa-type GaAs layer region is Such a structure is not preferred because it tends to grow on 27a.

Next, before growing the second layer 29 for the upper cladding layer of n-AlGaAs, an unsaturated GaAs solution is grown.
When melt-backed, the AlGaAs anti-melt-back layer 28 is hardly melted back.
Only the mesa-shaped region 27 of the GaAs layer is melted back, and this meltback reaches the lower first layer 23 for the upper cladding layer made of n-AlGaAs.

Generally, it is difficult to perform liquid phase growth on an AlGaAs layer once exposed to air, but growth is possible immediately after performing such meltback. Therefore, in this case, the second layer 29 for the upper cladding layer made of the same AlGaAs can be easily grown on the first layer 23 for the upper cladding layer made of AlGaAs. With this first layer 23 and second layer 29,
A sufficiently thick upper cladding layer is formed above the oscillation region 31. Next, on this second layer 29, n-
A cap layer 30 is formed by growing GaAs to obtain a wafer structure as shown in FIG. 1D. In this case, the GaAs layer 24 and the anti-melt back layer 28
becomes a current confinement layer. Moreover, this GaAs layer 24
also acts as a light absorption layer. Next, although not shown, an upper electrode and a lower electrode are attached to this wafer structure to obtain a semiconductor laser.

A bias voltage is applied between the electrodes of this semiconductor laser, the n-GaAs cap layer is used as a negative electrode, and the substrate 2 is
When operated with the 0 side as the positive electrode, n-AlGaAs
The first layer 23 for the upper cladding layer and the current confinement layer 2
4 is in a reverse bias state, and the active layer 22
is efficiently concentrated in the central oscillation region 31. In addition, the first layer 23 of n-AlGaAs immediately below the GaAs layer 24 as a current confinement layer is as thin as about 0.3 μm, so light cannot be confined in this part, and the upper
It is absorbed by the GaAs layer 24. Therefore, oscillation occurs only in the oscillation region 31 at the center of the active layer 22, resulting in stable oscillation in the transverse fundamental mode.

In the above-described embodiments, the conductivity type of the substrate is n-type, but it is also possible to use a p-type substrate and manufacture a laser element having a structure in which the conductivity types of each layer are inverted correspondingly.

(Effects of the Invention) As is clear from the embodiments described above, according to the present invention, the first layer for the lower cladding layer, the active layer, and the upper cladding layer is formed on the flat surface of the substrate before forming the grooves. Since these layers are grown in a liquid phase, the thickness of these layers can be easily and easily controlled to be thin, and each layer can be grown flat.

In addition, double dovetail grooves were dug in the GaAs for the current confinement layer with appropriate groove width and groove spacing.
Since the anti-meltback layer AlGaAs is grown on the GaAs layer, this AlGaAs can be prevented from growing at all on the mesa-shaped GaAs layer region between the two grooves, and therefore meltback can be performed with good reproducibility. I can do it.

In addition, the
AlGaAs on first layer for upper cladding layer of AlGaAs
Since the second layer is grown, the growth can be performed satisfactorily.

[Brief explanation of drawings]

1A to 1D are manufacturing process diagrams showing an example of a method for manufacturing a semiconductor laser according to the present invention, FIG. 2 is an explanatory diagram for explaining a double dovetail groove used in the present invention, and FIGS. 3A and B are FIG. 2 is a manufacturing process diagram for explaining a conventional semiconductor laser manufacturing method. 20...Substrate, 20a...Substrate surface, 21...Lower cladding layer, 22...Active layer, 23...First layer for upper cladding layer, 24...GaAs layer for current confinement (or current confinement layer), 24a, 24b...GaAs surface of the layer, 25
...First groove, 25a, 26a... Bottom surface of groove, 26... Second groove, 25b, 26b... Side surface of groove, 27... Mesa-shaped region, 27a... Surface of mesa-shaped region, 28... Anti-melt back layer, 29... Second layer for upper clad layer, 30... Cap layer, 31... Oscillation region.

Claims (1)

[Claims] 1. Manufacture an AlGaAs/GaAs semiconductor laser comprising a GaAs current confinement layer on a GaAs substrate, and a lower cladding layer, an active layer, and an upper cladding layer each formed of AlGaAs and forming a double heterostructure. In order to do this, there is a step of sequentially growing a lower cladding layer, an active layer, a first layer for the upper cladding layer, and a GaAs layer for current confinement on the flat surface of the substrate, and a step of growing the GaAs layer with a dovetail cross-sectional shape. forming first and second grooves in a stripe shape and parallel to each other on the grooved GaAs layer;
A step of growing an anti-meltback layer of AlGaAs so that the GaAs layer is exposed, and a step of removing the GaAs layer region between the two grooves down to the first cladding layer using the difference in meltback speed between AlGaAs and GaAs. A method for manufacturing a semiconductor laser, comprising the steps of: forming three grooves; and growing a second layer for an upper cladding layer in the third groove and on the anti-melt back layer.