JPH0740621B2 - Method for manufacturing surface-emitting type semiconductor laser - Google Patents

Description

The present invention relates to a method for manufacturing a surface-emitting type semiconductor laser having an internal current confinement structure.

[Prior art]

Generally, a surface-emitting type semiconductor laser has a structure in which a resonator is formed between the substrate surface and the epitaxial growth layer surface and emits light in the surface direction.
Alternatively, it is possible to integrate the laser element and the peripheral electronic circuit, and it becomes possible to perform monolithic processing that does not require manual work for cleavage, and it is easy to obtain single longitudinal mode oscillation.
In addition, since the light emission spot is large, it has advantages such as a sharp beam emission angle, and the development thereof has been advanced in recent years.

Even in such a surface-emitting type semiconductor laser, it has been attempted to adopt an internal current confinement structure capable of partially concentrating the current density to reduce the threshold current and improve the light emission efficiency.

The internal current confinement structure itself has already been widely adopted in inner stripe type semiconductor lasers and the like, and it is already known to use the meltback method, which requires a small number of man-hours, for manufacturing (Spring Society of Applied Physics, 1983. 7P-H-
7).

FIG. 8 is a cross-sectional structural view of a conventional inner stripe type semiconductor laser, in which a block layer 12 made of AlGaAs having a conductivity type of p-type is formed on a GaAs substrate 11 having a mesa stripe structure and a conductivity type of n-type. Then, the whole is melted back by contacting with an unsaturated Ga-As melt. Since the p-type AlGaAs layer grown on the peripheral surface of the mesa is thin, the substrate is first formed at this part.
11 is exposed and a V groove 11a is formed.

Therefore, following this, the cladding layer 1 made of n-type AlGaAs
3, an AlGaAs active layer 14 and a p-type AlGaAs clad layer 15 are grown in this order to manufacture an inner stripe type semiconductor laser having a refractive index guiding structure and a current constriction structure.

[Problems to be solved by the invention]

By the way, in the method of forming the current constriction structure using the meltback method as described above, since the mesa portion 11a made of GaAs is directly formed on the surface of the substrate 11, the substrate itself is partially removed by etching. There is a problem that it cannot be applied as it is to the surface emitting semiconductor laser.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method of manufacturing a surface-emitting type semiconductor laser in which an internal current constriction structure can be easily built by using a meltback method. It is in.

[Means for solving problems]

A method of manufacturing a surface-emitting type semiconductor laser according to the present invention comprises a blocking layer for stopping meltback on a substrate, a first crystal growth step of forming one or a plurality of layers on the blocking layer, and a surface layer. After an etching step of forming a mesa portion on the film, and forming a current blocking layer on the layer on which the mesa portion is formed,
A step of selectively melting back the current blocking layer in the mesa portion and a portion corresponding to the mesa portion to form a concave hole so as to reach the blocking layer; and a step of backfilling the concave hole on the current blocking layer. And a second crystal growth step of forming an active layer and another cladding layer on the cladding layer in this order.

In particular, the method is characterized in that a step of etching a window reaching the blocking layer is formed under the concave hole of the substrate, and the blocking layer stops this etching.

[Action]

According to the method of the present invention, the crystal growth step can be performed in two steps, and the characteristics can be greatly improved by the internal current confinement structure.

〔Example〕

The present invention will be specifically described below with reference to the drawings showing the manufacturing process thereof. FIGS. 1 to 7 are process diagrams of the method of the present invention. First, as shown in FIG. 1, in the first crystal growth process, a p-type GaAs substrate 1 of conductivity type is formed by a liquid phase epitaxial growth method.
The conductivity type is the same as that of the substrate 1, that is, p-type Ga _1-x Al _x As (x ≧ 0.
A blocking layer 2 for stopping the melt-back and etching of 1) and a mesa portion forming layer 3 of p-type GaAs which also serves as an anti-oxidant of the blocking layer 2 are laminated in this order.
Then, in the etching process, as shown in FIGS. 2 and 3, a diameter of 5 to 10 μm and a height of 0.5 are formed in the substantially central portion of the surface of the mesa portion forming layer 3.
A mesa portion 3a having a thickness of 2 μm is formed.

Next, in the second crystal growth step, similarly, as shown in FIG. 4, the n-type Ga of the n-type conductivity type is first formed over the entire surface of the p-type GaAs layer 3 including the mesa 3a as shown in FIG.
After forming the block layer (current block layer) 4 made of _1-y Al _y As (y ≧ 0.1), the mesa portion 3a and the corresponding block layer 4 as shown in FIG. The mesa portion forming layer 3 is removed from the surface side to the surface of the blocking layer 2 so that a cylindrical concave hole 3b is formed.

The meltback method utilizes the fact that the Ga _1-y Al _y As crystal forming the block layer 4 and the GaAs crystal forming the mesa portion forming layer 3 have large meltback speeds in the As unsaturated melt. And the As unsaturated on the surface of the block layer 4.
When the Ga-As melt is brought into contact, the block layer 4 first melts, and when the block layer 4 melts to a predetermined thickness, the surface of the mesa 3a is exposed in the thin mesa 3a forming portion of the block layer 4. The melting rate of the GaAs crystal forming the mesa 3a is AlGa
As a result of being significantly larger than that of As crystal, the mesa portion 3a melts rapidly, and a cylindrical concave hole reaching the surface of the blocking layer 2 there.
3b will be formed.

Subsequently, as shown in FIG. 6, the conductivity type is p-type Ga _1-z Al _z As
An internal current constriction structure is formed by forming a cladding layer 5 made of (z ≧ 0.3) to a required thickness on the surface of the block layer 4 in a manner of filling the cylindrical concave hole 3b, and further forming a conductive type layer thereon. Is a p-type Ga _1-w Al _w As (w ≦ 0.15) active layer 6 and a conductivity type is an n-type Ga _1-z Al _z As clad layer 7, and is a double heterojunction layer consisting of three layers. Of the conductivity type n
The cap layer 8 made of Ga _1-v Al _v As (v ≦ 0.15) of the mold is laminated.

Finally, as shown in FIG. 7, the lower surface of the substrate 1 and the cap layer 8 are formed.
Electrodes 9u and 9d are formed on the upper surface, and a reflecting mirror 10u is provided at the center of the electrode 9u and at a position corresponding to the internal current constriction.
In addition, an emission window 1a that penetrates the substrate 1 and reaches the blocking layer 2 is formed by etching in the center of the electrode 9d, and a reflecting mirror 10d is formed on the exposed surface of the block layer 2 to form an internal current constriction structure. A surface-emitting type semiconductor laser having

In such surface emitting semiconductor lasers, electrodes 9u and 9d
By applying a required voltage in between, a current flows through the narrowed portion, and light is repeatedly moved between both reflecting mirrors 10u and 10d to be resonated, and emitted in the direction of the white arrow.

Next, specific numerical examples of the electric conductivity, component composition, and film thickness in the case of using the p-type GaAs substrate for each layer are as follows.

Substrate 1 ... p-type GaAs substrate Blocking layer 2 ... p-type Ga _0.6 Al _0.4 As blocking layer (film thickness: within 1 to 10 μm) Mesa portion forming layer 3 ... p-type GaAs mesa portion forming layer (film thickness: 1.5 μm
Mesa part 3a… Diameter: 5μm, Height: within 1μm Block layer 4… n-type Ga _0.6 Al _0.4 As block layer clad layer 5… p-type Ga _0.6 Al _0.4 As clad layer active layer 6… p-type Ga _0.9 Al _0.1 As active layer Clad layer 7 ... N-type Ga _0.6 Al _0.4 As clad layer Cap layer 8 ... N-type Ga _0.85 Al _0.15 As cap layer In the above-mentioned embodiment, the case of using p-type GaAs for the substrate has been described. N-type GaAs may be used. In this case, the p-type of each of the above layers may be n-type, and the n-type may be p-type.

In the above embodiment, the case of manufacturing a GaAs surface emitting semiconductor laser has been described.
Of course, it can be applied to an InP-based surface-emitting type semiconductor laser.

〔effect〕

As described above, according to the method of the present invention, a surface-emitting type semiconductor laser having an internal current confinement structure is manufactured by the three steps of the first and second crystal growth steps and the etching step for forming the mesa portion. And the manufacturing process is simplified, and the characteristics can be greatly improved, which is an excellent effect.

[Brief description of drawings]

1 to 7 are explanatory views showing the manufacturing process of the method of the present invention, and FIG.
FIG. 1 is a sectional structural view of an inner stripe type semiconductor laser having a conventional internal current confinement structure. 1 ... Substrate, 2 ... Blocking layer, 3 ... Mesa portion forming layer, 3a ... Mesa portion, 3b ... Recessed hole, 4 ... Block layer, 5 ... Clad layer, 6 ...
Active layer, 7 ... Clad layer, 8 ... Cap layer

Claims (2)

[Claims] 1. A first crystal growth step of forming a blocking layer for stopping meltback on a substrate and one or a plurality of layers on the blocking layer, and an etching step of forming a mesa portion in a surface layer. And forming a current blocking layer on the layer on which the mesa portion is formed, and then selectively melting back the current blocking layer in the mesa portion and the portion corresponding to the mesa portion so as to reach the blocking layer. A second crystal growth in which a clad layer is formed on the current blocking layer in a manner of backfilling the concave hole, and an active layer and another clad layer are laminated in this order on the clad layer. And a step of manufacturing a surface-emitting type semiconductor laser. 2. A step of etching a window reaching the blocking layer under the recessed hole of the substrate, wherein the blocking layer stops the etching.
A method for manufacturing the surface-emitting type semiconductor laser described.