JPS6119185A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To control an active layer in a V groove reaching to an N type substrate thinly by a method wherein a P layer is superposed onto the substrate, the V groove is formed, and the surface of a P type current block layer except the V groove at a slow crystal growth rate is etched, and changed into a surface, a crystal growth rate thereof is faster than that of the surface in the V groove. CONSTITUTION:P-InP2 is superposed onto an N-InP(100) face 1a, a V groove 3 is formed through etching, and the layer 2 on the outside of the V groove 3 is etched by HCl+H3PO4 to shape grooves 11. The depth of the groove 11 takes size in which the surface is not formed in a (100) face through a burying with the next N-InP4, and a V shape may not be adopted as a form when the crystal growth rate of the surface of the groove 11 is faster than that of the upper section of the surface of the V groove 3. An N-InP clad 4, a GaInAsP active layer 5, a P-InP clad 6 and a P-GaInAsP cap 7 are shaped in an epitaxial manner in the liquid phase, and a residual section in the layer 2 is used as a current block. According to said constitution, a solute 9 is also employed for the growth of the active layer in the groove 11, and does not move concentrically into and near the V groove 3, thus controlling the growth of the active layer in the groove 3 extremely thinly.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a semiconductor laser that has a low threshold current and oscillates in a transverse fundamental mode.

(Prior art) Regarding the conventional manufacturing method of such a semiconductor laser, see 1.
For example, literature (IEEE Journal of Qua
ntumElectronics, QE21B,
[103, (11382), p, 1704-171
1). The structure and manufacturing process of this conventional semiconductor laser will be briefly explained with reference to FIGS. 3(A) and 3(B).

As shown in FIG. 3A, p-InP crystals are grown as a second conductivity type layer 2 on a (100) substrate surface 1a of an n-1nP substrate 1 having a first conductivity. The surface of this p-1nP layer 2 is a (100) plane in this case. Next, using etching mask such as 5i02, grooves 3 with a stripe direction in the (011) direction and a figure-7 cross section are formed at a depth reaching a part of the substrate 1 from the surface of this p-1nPJij2. Form by etching.

The etchant used for this etching is HI:JL.
When H3PO4 is applied, the surface of the v-groove 3 becomes the (111) B surface.

Next, liquid phase epitaxial growth is performed on the surface of the V groove 3 and the remaining portions 2a and 2b of the p-1nP layer 2 to form n-InPn chips and Ga InAsP as the first conductivity type cladding layer 4. The active layer 5, the P-InPn chip 9 as the second conductivity type cladding layer 6, and the p-Ga1nAsP cap layer as the second conductivity type cap layer 7 are crystal-grown in sequence, and the cross-sectional view shown in FIG. 3(B) is obtained. Obtain a wafer structure as shown.

This wafer structure has its cap layer 7 as a positive electrode, and
When the substrate 1 is used as a negative electrode, ■ p -In outside the groove 3
The interface between the P block layer 2 and the n -1nP cladding layer 4 is reverse biased, and the structure is such that current flows only inside the V groove 3, thereby enabling low threshold oscillation.

Also, from the above-mentioned literature, in this structure, the width W of the region of the active layer 5 inside the V groove 3 is about 1.5 JL, and the thickness d of the central part of this region is 0.5 JL. 1 gya
It is known that stable oscillation in the transverse fundamental mode can be obtained by setting the

(Problems to be Solved by the Invention) However, in the case of this conventional structure, the thickness d of the central portion of the active layer 5 is set to 0.1 p for the following reason.
It was extremely difficult to reduce the thickness to about ta or less. That is, when growing the active layer 5, since the plane of the V-groove 3 is the (111) B plane, the active layer 5 grows on the n-1nP cladding layer 4 grown on this plane within the groove.
On the other hand, the plane of the current blocking layer 2 outside the structure is the (100) plane. In this case, as shown in FIG. 4, the solute 9 in the solution inside the V-groove 3 and in the vicinity of the growth solution 8 is more likely to be generated as nuclei than the solute 9 in other parts, and the concentration of the solute 9 is becomes thinner, and therefore, the solute 9 in the solution portion on the flat surface outside the V-groove 3 moves to the vicinity or inside the V-groove 3 as shown by the arrow IO. Therefore, in this growth, nuclei are more likely to be generated inside the V-groove 3, and the growth rate is considerably faster than that outside the groove. Therefore, even if the growth time is about 1 second, the growth will be 0.2071 m or more. As described above, it is extremely difficult to accurately control the thickness of the active layer 5 grown within the V-groove.

An object of the present invention is to provide a method for manufacturing a semiconductor laser that can control the thickness of an active layer grown in a groove to be thin.

(Means for Solving the Problems) In order to achieve this object, according to the present invention, the surface of the current blocking layer, which is a second conductivity type layer outside the structure, and which conventionally had a slow crystal growth rate, is etched. The gist is to change the surface to a surface where the crystal growth rate is higher than that of the surface inside the V-groove.

Therefore, according to the present invention, after a second conductivity type layer is grown on the substrate surface of the first conductivity type substrate, etching is performed from the surface of the layer until reaching a part of the substrate to form a current path. After that, a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer are grown by liquid phase epitaxial growth to form a striped first groove having a figure-7 cross section. In manufacturing a semiconductor laser in which the remaining portion of the conductivity type layer is used as a current blocking layer, in a step before or after forming the first groove, the second conductivity type layer outside the first groove is etched to form a crystal. Continuously forming a plurality of second grooves having surfaces whose growth rate is the same as or higher than the crystal growth rate on the surface of the first groove, and then
The method is characterized in that the liquid phase epitaxial growth is performed on the surfaces of the first groove and the second groove under the same growth conditions.

(Function) By doing this, (1) the growth of the active layer on the surface of the current blocking layer outside the structure will be as fast as or faster than the growth inside the V-groove, so that the solute will (1) be absorbed into the groove and its vicinity. Since concentration can be suppressed and the growth rate of the active layer within the groove can be slowed down, an active layer with a thickness of about 0.1 gm or thinner can be grown with good control.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIGS. 1A and 1B are main manufacturing process diagrams for explaining the manufacturing method of the present invention, and FIG. 2 is a diagram for explaining the invention. In addition, in these figures, the same components as those shown in FIGS. 3 (A) and (B) and FIG. .

(100) of n-InP substrate 1, which is the first conductivity type substrate.
A p-1nP layer 2, which is a second conductivity type layer, is laminated on the substrate surface la. In this case, the surface of this layer 2 also becomes a (100) plane. According to this invention, after forming the groove 3 (in this case, this groove 3 is the -th groove) by etching for forming a current path, or before forming the groove 3, The surface of the p-1nP layer 2 outside the V-groove 3 is HC-treated.
A plurality of second grooves 11 are continuously formed by etching using a mixed etchant of fL, H, and PO. and,
The surface of the second groove 11 obtained by this etching is made into a surface such that the crystal growth rate on this surface is the same as or faster than the crystal growth speed on the V-groove 3 surface. Since the surface of the V groove 3 is the (111) B surface, if the surface of the second groove 11 is set as the (+11) B surface, it becomes the same surface as the −th groove 3 surface. Therefore, by this etching, the surface of the p-InP layer 2 is changed to a surface where the crystal growth rate of the second grooves 11 formed continuously is high.

The size of the second groove 11 needs to be such that when the n -1nP layer 4 is grown, it will not be buried and the surface will not become a (100) plane.

Further, the shape of the second grooves 11 may be striped or other shapes, and as described above, the surfaces formed by etching of the second grooves 11 increase the crystal growth rate. It is sufficient that the surface has a growth rate higher than that of the V-groove 3 surface.

On each surface of these first and second grooves 3 and 11, a first conductivity type cladding layer is formed under normal conditions as in the past.
-1nP cladding layer 4, GaInAsP active layer 5, p-1nP layer 6 which is a second conductivity type cladding layer, and p-Ga
InAsP cap layer 7 is sequentially grown by liquid phase epitaxial growth to obtain a semiconductor laser wafer structure in which the remaining portion of p -1nP layer 2 is used as a current blocking layer.

As described above, the growth of the Ga InAsP active layer 5 is fast on the surface of the second groove 11 of the p-InP layer 2, so that the solute 9 in the portion outside the V groove 3 of the growth solution 8 is is used for active layer growth in the second groove 11, so there is no concentrated movement of the solute 9 into the V groove 3 and its vicinity as in the conventional case, and the solute 9 does not move anywhere on the V groove 3 and the second groove 11. The growth conditions are almost the same.

Therefore, the active layer 5 does not grow faster in the groove 3 than in other parts. Therefore, the growth of the active layer within the V-groove 3 can be controlled to a thickness of 0.1 gra or thinner within a few seconds.

The operating principle of the semiconductor laser having the structure thus obtained is the same as that of the conventional structure, and therefore the explanation thereof will be omitted.

In the embodiments described above, the first conductivity type is the n-conductivity type and the second conductivity type is the p-conductivity type, but the conductivity types may be opposite to each other.

Furthermore, in the above-mentioned embodiments, a Ga1nAsP/InP-based semiconductor laser using an InP substrate was described, but the invention is not limited to this.
The present invention can also be applied to aAs/GaAs semiconductor lasers. In the latter case, a mixture of NH40H, H2O2, and H2O can be used as the etchant.

(Effects of the Invention) As is clear from the above description, according to the present invention, by selecting the combination of the material and etchant used to form the current blocking layer, V for forming the current path can be reduced. Separately from the groove, a second groove is formed on the surface of the second conductivity type layer serving as the current blocking layer so that the crystal growth rate is the same as or higher than that on the V-groove plane. The surface of this second conductivity type layer is changed to the surface of the second groove mentioned above, and the active layer is laminated by liquid phase epitaxial growth on each surface of these first and second grooves. It is possible to avoid concentration of solutes in the growth solution in the vicinity. Therefore, (1) the growth of the active layer within the groove can be made slower than before, and therefore, the active layer can be grown more easily than before. It can be grown to ip, tm or thinner.

[Brief explanation of drawings]

1(A) and (B) are manufacturing process diagrams for explaining the manufacturing method of the semiconductor laser of the present invention, FIG. 2 is a diagram for explaining the present invention, and FIG. 3(A) and (B). ) is a manufacturing process diagram for explaining a conventional semiconductor laser manufacturing method, and FIG. 4 is a diagram for explaining the conventional method. l...First conductivity type substrate 1a...Substrate surface, 2...Second conductivity type layer 2a
, 2b...Current blocking layer 3...■groove (first groove) 4...First conductivity type cladding layer 5...Active layer, 6...Second conductivity type cladding layer 7... Second conductivity type cap layer 8...Growth solution 9...Solute 10...Arrow 11 (indicating movement of solute)...Second groove.

Claims (1)

[Claims] 1. After growing a second conductivity type layer on the substrate surface of the first conductivity type substrate, etching is performed from the surface of the layer until reaching a part of the substrate to form a current path. A stripe-shaped first groove having a V-shaped cross section is formed for the purpose of forming the second conductive type cladding layer, and then a first conductive type cladding layer, an active layer, and a second conductive type cladding layer are grown by liquid phase epitaxial growth. In manufacturing a semiconductor laser in which the remaining portion of the conductivity type layer is used as a current blocking layer, in a step before or after forming the first groove, the second conductivity type layer outside the first groove is etched to form a crystal. successively forming a plurality of second grooves each having a surface whose growth rate is the same as or higher than the crystal growth rate on the surface of the first groove; A method for manufacturing a semiconductor laser, characterized in that the liquid phase epitaxial growth is performed under the same growth conditions as above. 2. In the method for manufacturing a semiconductor laser according to claim 1, the substrate surface is a (100) plane, and the second conductivity type layer formed by the first groove surface and the second groove is A method for manufacturing a semiconductor laser, characterized in that each surface is a (111)B plane.