JPS61202488A - Manufacture of buried semiconductor laser - Google Patents

Abstract

PURPOSE:To improve a manufacturing yield by growing a paired substrate reverse conductive type block layers for burying both sides of strip mesa which contains an active layer of double hetero junction thickly to become higher than the upper surface of the mesa, thereby suppressing the improper growth. CONSTITUTION:An InGaAsP active layer 2 and a P<+> type InP clad layer 3 are grown on an InP substrate 1. A mask film 5 of SiO2 is formed to form a strip thereon, with it as a mask it is mesa etched to form a mesa 6 in a reverse mesa. Then, P<+> type InP block layers 9 are grown at both sides of the mesa 6, and then an N<+> type InP block layer 8 a P-type InP layer 13 are grown. Then, the film 5 is removed, a P<+> type InP layer 13 and a P<+> type InGaAsP contacting layer 14 are grown on the entire surface, and metal electrodes 9, 10 ohmically contacted with the upper and lower surfaces are coated to complete a semiconductor laser.

Description

DETAILED DESCRIPTION OF THE INVENTION (Summary) A method for manufacturing a buried semiconductor laser, in which a blocking layer of opposite conductivity to the substrate is filled on both sides of a band-shaped mesa including an active layer forming a double heterojunction, and By growing the block layer thicker to a higher thickness, it is possible to suppress the occurrence of defective growth spots, which have conventionally occurred frequently in the block layer, and improve the manufacturing yield.

[Industrial application field]

The present invention relates to a method for manufacturing a buried semiconductor laser in which both sides of a band-shaped mesa including an active layer forming a double heterojunction are buried with a block layer, and particularly to a method for forming the block layer.

□Semiconductor lasers have come to be widely used as optical signal sources for optical communication and information processing, which use light as a medium to handle large amounts of information.

The semiconductor laser used in this way has good characteristics (
For example, it is desired that the oscillation threshold current is small and the efficiency is high) and that the manufacturing yield is also high.

(Prior Art) As a typical conventional semiconductor laser with low threshold current and high efficiency, the manufacturing procedure is shown in the process-order side cross-sectional views of FIGS. 3(a) to (C). There is a semiconductor laser.

That is, first of all, [see figure (al)], n-type indium phosphide (InP
) on a substrate l of indium gallium arsenide phosphide (InGa
AsP) active layer 2, p + type InP cladding layer 3, p
A contact layer 4 of + type 1nGaAsP is grown. A band-shaped mask film 5 of silicon dioxide (Si02) is formed on top of the mask film 5, and this is used as a mask for mesa etching, resulting in a band-shaped mesa whose lower part is narrower than its upper part (a so-called reverse mesa) 6.
form.

The reason why the mesa 6 is an inverted mesa is that it becomes easy to reduce the width of the active layer 2 in order to improve the characteristics of the semiconductor laser.

Next [see figure (b)], p+ type 1nP is placed on both sides of mesa 6.
The block layer 7 is grown to be as thin as possible so as to fill the active layer 2, and the n+ type InP block layer 8 is grown thereon to the extent that the mesa 7 is just filled.

Next (see Figure (C)), the mask film 5 is removed and metal electrodes 9 and 10 are deposited on the upper and lower surfaces, respectively, in ohmic contact to complete the semiconductor laser.

In this semiconductor laser, the active layer 2 forms a double heterojunction, and when a current is passed between electrodes 9 and 10 with electrode 9 being positive, a current flows at the P-N junction between blocking layers 7 and 8. Also, since the junction area between the cladding layer 3 and the block layer 7 is small and the rise voltage at the junction surface between the block layer 7 and the substrate 1 is larger than the rise voltage at the active layer 2 region, the leakage current shown by a is The current is suppressed and concentrated in the active layer 2 region, and laser light is emitted from the active layer 2 with a low threshold current and high efficiency.

[Problem that the invention seeks to solve]

However, in the above manufacturing method, in the growth of the block layer 7 shown in Figure (b), since the thickness of the block layer 7 is thin, there are often defective growth spots 11 as shown in Figure 4, which corresponds to Figure (C). There is a problem in that the manufacturing yield is reduced due to the leakage current shown by b.

[Means for solving problems]

The above problem can be solved by growing a multilayer semiconductor film including an active layer 2 forming a double heterojunction on a -conductivity type semiconductor substrate 1, and then using mesa etching to solve the above problem, as shown in the cross-sectional side view of FIG. A step of forming a band-shaped mesa 6 including the active layer, and forming a blocking layer 7 of a semiconductor of an opposite conductivity type on both sides of the mesa 6.
This problem is solved by a manufacturing method including a step of growing the mesa 6 until it becomes higher than the upper surface of the mesa 6.

[Effect]

In conventional manufacturing, in order to suppress the leakage current a shown in FIG.
The growth thickness of the block layer 7 was made thinner in hopes of increasing the rise voltage at the junction surface with the substrate 1, but as explained in FIG.
(indicated by a broken line in Fig. 1).

In the present invention, the leakage current a is suppressed depending on the bonding surface between the block layer 7 and the substrate 1, and the thickness of the block layer 7 is made thick so as to prevent the occurrence of defective growth portions 11. When forming the mesa 6, the thickness is sufficient to eliminate the occurrence of defective growth spots 11 by growing it to a height higher than the upper surface of the mesa 6.

The inventor of the present application believes that a semiconductor laser manufactured using the present manufacturing method has almost the same characteristics as a good semiconductor laser manufactured using the method shown in FIG. It was confirmed that the manufacturing yield was improved.

This means that the leakage current a can be suppressed between the blocking layer 7 and the substrate 1.
This proves that the leakage current shown in FIG. 4 has been significantly reduced.

〔Example〕

An example of manufacturing a semiconductor laser by the method of the present invention will be described below with reference to step-order side cross-sectional views of FIGS. 2A to 2C showing the manufacturing procedure.

That is, first of all, see [Figure +8]], n-type indium phosphide (InP
) on the substrate 1 of indium gallium arsenide phosphide (InGa
A silicon dioxide (Si02
) is formed, and mesa etching is performed using this as a mask to form a mesa 6 forming an inverted mesa similar to that shown in FIG. 3fa).

Next [see figure (b)], p+ type 1nP is placed on both sides of mesa 6.
The block layer 7 is grown until it becomes higher than the upper surface of the mesa 6. By doing so, the block layer 7 becomes thick enough to eliminate any defective growth areas. Subsequently, an n+ type InP block layer 8 and a p type 1nP layer 12 are formed thereon.
and grow.

Next [see figure (C)], after removing the mask film 5 and growing a ρ1-type 1nP layer 13 and a ρ"-type InGaAsP contact layer 14 on the entire surface, metal electrodes 9 are formed to make ohmic contact with each of the upper and lower surfaces. and 10 are deposited to complete the semiconductor laser.

In this semiconductor laser, the concave shape of the mesa 6 on the top surface due to the growth shown in Figure (b) is compensated for by the p+ type InP layer 13 to make the top surface flat, making it easier to mount the finished product. There is. Note that the p-type 1nP layer 12 is p+ type I
It functions to suppress diffusion of high concentration impurities in the nP layer 13 into the n+ type block layer 8.

The inventor of the present application has proposed the method of the illustrated embodiment in FIG. 2 and the conventional third method.
By the method shown in the figure, the cross-sectional dimension of the active layer 2 is set to a width of about 1 μm.
m, a semiconductor laser with a thickness of about 0.15 μm was manufactured,
The characteristics of both good products are that the oscillation threshold current is approximately 20mA.
It was confirmed that there was no difference in the differential quantum efficiency of about 25%. Furthermore, the defect rate due to leakage current when using the method of this embodiment is reduced by about one order of magnitude compared to when using the conventional method.

〔Effect of the invention〕

As explained above, according to the configuration of the present invention, leakage can be prevented without deteriorating the characteristics in manufacturing a buried semiconductor laser in which both sides of a band-shaped mesa including an active layer forming a double heterojunction are buried with blocking layers. It is possible to provide a manufacturing method that reduces defects caused by current, and has the effect of making it possible to improve the manufacturing yield of the semiconductor laser suitable for an optical signal source.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view showing the gist of the present invention, and Fig. 2 (al~
(C) is a process-order side cross-sectional view showing an example of semiconductor laser manufacturing by the method of the present invention; FIGS. 3 is a side sectional view showing problems in the manufacturing shown in FIG. 3. In FIGS. 1 to 4, 1 is an n-type substrate, 2 is an active layer, 3 is a p+-type cladding layer, 6 is a mesa, 7 is a ρ" type block layer, 8 is an n+ type block layer, 11 is a growth failure area, and a and b are leakage currents. Agent: Patent attorney Hiroshi Matsuoka Figure 17: Side cut showing the layer point 2 g, $4

Claims (1)

[Claims] A step of growing a multilayer semiconductor film including an active layer (2) forming a double heterojunction on a semiconductor substrate (1) of one conductivity type, and forming a band-shaped mesa (6) including the active layer (2) by mesa etching. and growing block layers (7) of opposite conductivity type semiconductors on both sides of the mesa (6) until they are higher than the upper surface of the mesa (6). manufacturing method.