JPS61265888A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To enable a coating on the numerous end faces of a semiconductor laser to be performed at a time and to very simplify the coating onto the end faces by a method wherein plural grooves are kept formed by a reactive ion etching method and a dielectric film is formed in such a way as to cover at least the sidewalls of the grooves. CONSTITUTION:An N-type Al0.3Ga0.7As buffer layer 2 of 3mum thickness, a non-doped Al0.1Ga0.9As active layer 3 of 0.1mum thickness, a P-type Al0.3Ga0.7As clad layer 4 of 2mum thickness and a P-type GaAs cap layer 5 of 1mum thickness are made to epitaxially grow in order on an N-type GaAs substrate 1, and after that, a P-side electrode 6 consisting of Cr and Ar and an N-side electrode 7 consisting of Au, Ga and Ni are respectively formed on the P-type GaAs cap layer 5 and under the N-type GaAs substrate 1. Then, 20mum wide grooves 8, each having its side surface vertical to the active layer 3, are formed in the semiconductor wafer deeper than the active layer 3 at an interval of 300mum by an RIE method, and after that, an about 2,800Angstrom thick SiO2 film 9 is formed on the whole surface. Moreover, parts of the SiO2 film 9, which are located at a flat part 10 other than the grooves 8, are removed, the electrode 6 is made to expose and the wafer is cut at the groove parts 8, whereby the semiconductor laser in the desired groove parts 8, whereby the semiconductor laser in the desired constitution is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a method of manufacturing a semiconductor laser in which the end facets are easily coated.

(Prior art and its problems) Various characteristics of semiconductor lasers cannot be improved by coating their end faces. For example, in AjGaAs/GaAs semiconductor lasers that oscillate in a short wavelength band, it is difficult to improve the laser output In this case, end face damage (hereinafter referred to as COD) occurs on the end face due to oxidation of HP, etc., but this COD can be prevented by coating the end face with a dielectric film or the like. Therefore, it is common knowledge that semiconductor lasers using this material are coated with a coating on the end facets.In addition, the front facet of the semiconductor laser has an anti-reflection coating (hereinafter referred to as R-coating), and the rear facet has a reflective coating (hereinafter referred to as R-coating). ),
The end face reflectance becomes asymmetric, and high-output laser light can be obtained from the AR cocoing end face with low end face reflectance (No. 9).
International Semiconductor Laser Conference, lecture number C1). In addition, there is a method of applying an R coating to the output end face in order to improve the noise characteristics of a semiconductor laser with respect to the return light (Proceedings of the 31st Spring Conference on Applied Physics, No. 29a-M-9).
), or a method of ultra-multimode oscillation by applying FiA1'L coating (same as above, number 29p-M
-7)′! Nido is actually being tried.

By the way, when applying such a coating to the end face of a conventional semiconductor laser, the wafer for the semiconductor laser, which has even the busy electrodes formed, has a par shape with a total width of about 300 μm! ? The method used was to open the arm and coat the open surface with a dielectric film. At this time, care must be taken to prevent the coating film from wrapping around the electrode side, and it is dangerous to handle each extremely thin par by hand. Furthermore, one par is equivalent to ten semiconductor lasers. This process requires a lot of man-hours! L. Not suitable for mass production (Objective of the Invention) In order to solve these problems, the object of the present invention is to provide a manufacturing method in which coating the end face is extremely simple.

(Structure of the Invention) The manufacturing method according to the present invention includes the steps of forming a multilayer structure including at least an active layer, and forming a plurality of grooves that are deeper than the active layer and have sides perpendicular to the active layer. The present invention is characterized by comprising at least a step of forming a dielectric film, a step of forming a dielectric film so as to cover at least the side surfaces of the groove, and a step of cutting the multilayer semiconductor phenol at the groove portion.

(Principle of the invention) In recent years, reactive ion etching method (hereinafter referred to as RIFi)
Many attempts have been made to form the end face of a semiconductor laser using the method (referred to as the method). Electro Letters magazine, March 1983, Volume 19, Issue 6, Pages 213~
An example is shown at 215. Since the RIE method allows vertical etching of a semiconductor wafer, the etched surface can be used as a reflecting mirror in place of the arm-opening surface of a conventional semiconductor laser. In fact, the above paper states that a semiconductor laser having end faces formed by the RIB method achieved oscillation characteristics comparable to those of a device having arm openings at both ends. If this RIII method is used, the end face of a laser can be formed in the state of a semiconductor wafer, and if the entire dielectric film is formed on the semiconductor phenol thus obtained, the end face of several hundred semiconductor lasers can be formed at once. can be coated. Additionally, semiconductor wafers are easier to handle than conventional wafers. In this way, in this invention, a plurality of grooves are formed by etching, and a dielectric film is formed to cover at least the side walls of these grooves, making it possible to coat a large number of laser beam end faces at once. . This results in improved productivity.

(Example 1) The present invention will be explained in detail below using the drawings.

FIG. 1(d1) is a cross-sectional view of a semiconductor laser which is a first embodiment of the present invention, and FIGS. 1(a) to (c) are diagrams for explaining its manufacturing method. ), n-Ga
n-AA with a thickness of 3 μm on the As substrate 1! 0.3GaO
, 7As buffer layer 2, non-doped A with a thickness of 0.1μ
76, lGa0. gAs active layer 3, 2μ thick p-A
After epitaxially growing a 3Ga (1,7As) cladding layer 4 and a 1μ thick p-GaAs cap layer 5, a p-side electrode 6, n made of Cr/Au is applied onto the p-GaAs cap layer 5. -K AuGe under GaAs substrate 1
An n-side electrode 7 made of Ni is formed. In (b), grooves 8 with a width of 20 μm and deeper than the active layer 3 and perpendicular to the active layer 3 are formed in the semiconductor wafer at intervals of 300 μm using the RIB method.
Two films 9 are formed. In (C), the film 9 is removed from the flat portion 10 other than the groove 8, and the electrode 6 is exposed. By cutting the semiconductor wafer obtained in this way at the groove portion 8, a semiconductor laser having the desired structure shown in (d) is obtained. Therefore, even if the laser is operated at a high output of 100 mW or more, the COD characteristic of the AJGaAs7 aAs semiconductor laser will not occur. Furthermore, this semiconductor laser has an 810. The thickness of the films 11 and 12 is set to the oscillation wavelength of 0.
Since it is 1/2n6 times 81 μm (n6 is the refractive index of the 8i0. film and is approximately 1.45), the two end faces 11 and 12
The reflectance of is almost the same as that without coating, and there is no change in oscillation threshold current, external differential quantum efficiency, etc. due to coating. It is a sectional view of a semiconductor laser which is a second embodiment, and FIGS. 2(a) to 2(e) explain the manufacturing process thereof. It is a diagram. At (,), on the Fin-InP substrate 21, a buffer layer 22 with a thickness of 3 layers and a thickness of 0.1μ
m, a non-doped InGaAsP active layer 23 with a wavelength composition of 1.3 μm, a p-InP cladding layer 24 with a thickness of 2 μm, and a p”-In(hAsP) cap layer 25 with a thickness of 1 μm are sequentially epitaxially grown.
above the cap layer 25)? : A p-side electrode 6 made of Cr/Au and an n-side electrode 7 made of AuGeNi are formed under the n-InP substrate 1. In (b), trenches 8 with a vertical side surface and a width of 20 μm are formed in this semiconductor wafer at intervals of 300 μm, deeper than the active layer 23, by the RIFt method. to be accomplished. In addition, 930 thick + 1D8i film and 2200 thick Xosto,
A dielectric film 27 having a four-layer structure in which films are alternately repeated is deposited by sputtering from diagonally above the wafer. At this time, one side surface of the four-layer structure dielectric film 27Fi groove 8 and the flat part 10
Formed only in In (c), the flat portion 1004 layer structure dielectric film 27 and the 8iN film 26 are removed to expose the p-side electrode 6. By cutting the multilayer semiconductor wafer thus obtained at groove portions 8, the desired semiconductor laser shown in (d) was obtained. This semiconductor laser Kt? Including S
The thickness of the IN film 26 is 1/6 nN times the oscillation wavelength of 1.3 μm (nHtl; the refractive index of tSiN is approximately 1.85). The reflectance is as low as about 10%, and the 4-layer dielectric film 2
7, the thickness of the Si film and the 8i01 film was set to 1/4 ns of the oscillation wavelength (ns is about 3.5 with the refractive index of 8i).
) and 1/4n0 times, a four-layer dielectric film 27 is formed and the reflectance of the end surface is as high as about 80 cm. Therefore, due to the asymmetry of the end face reflectance, a high output of 100 mW or more can be obtained from the low reflectance end face 11 side.90 (Example 3) In the above example, the semiconductor wafer Kp side electrode 6 is formed. Although the method of forming the groove 8 and the dielectric films 9, 26, and 27 after the above steps has been described, in the third embodiment, a method of forming the p-side electrode 6 afterward will be described.

FIG. 3(d) is a sectional view of a semiconductor laser according to a third embodiment of the present invention, and FIGS. 3(a) to 3(.) are diagrams showing the manufacturing process thereof. The semiconductor laser is of the AlGaAs/can As type as in the first embodiment. In (3), □−
On a GaAs substrate 1, n-AjO, 30io, 7Aa layer 2, non-doped A4. lGa0. gAs active layer 3, p-person! . ,3GIO,7AI cladding layer' ,P
- GaAs cap layer Sfe is grown epitaxially. The thickness of each layer is the same as in the first embodiment. In (b), grooves 8 having a width of 20 μm and having a side surface perpendicular to the active layer 3 and which are deeper than the active layer 3 are formed at intervals of 300 μm in the semiconductor wafer. Furthermore, the entire surface is covered with 8i0. After forming the film 9, a window is opened in the 8i0z film 9 of the flat portion 10. (
In c), the p-side electrode 6 made of Cr/Au is formed only on the flat portion 10. The method for forming the p-side electrode 6 is to first form the p-side electrode 6 on the entire surface and then remove it in the groove portion 8, or to fill the groove portion 8 with resist, and then to form the p-side electrode 6 on the entire surface. , and then remove the p-side electrode 6 in the groove portion 8 by a step-off method. Furthermore, n-GaA
An n-side electrode 7 made of AuGeNi is formed under the s-substrate 1. By cutting the semiconductor wafer thus obtained at the groove portion 8, the desired semiconductor laser shown in (d) can be obtained. Similarly to the device shown in the first embodiment, this semiconductor laser did not cause any COD or the like even when operated at a high output of 100 mW or more.

Incidentally, in the embodiment of the present invention, the RIE method is used to form the grooves 8, but the formation method is not limited to this, and for example, an ion milling method or a wet etching method may be used. Further, in the embodiment of the present invention, by cutting the semiconductor wafer at the groove portion 8, two etched end faces 11, 1 are formed.
However, according to the present invention, it is also possible to manufacture a semiconductor laser in which only one end face is formed by etching and the other end face is formed by a groove. 8 should be approximately 600 μm apart, and the semiconductor wafer may be placed between the bones near the center of the groove portion 8 and the flat portion 10. Further, the semiconductor laser may be a DFB laser having a diffraction grating inside the element.

(Effects of the Invention) The process of coating the end face of a semiconductor laser according to the present invention has the advantage that the semiconductor laser can be handled in a wet state and a large number of devices can be coated at once. is easy and suitable for mass production. However, by manufacturing a large number of devices at once, variations in the reflectance of the coated end faces of each device can be suppressed to a small extent, and therefore, the uniformity of device characteristics is also improved.

[Brief explanation of drawings]

1 to 3 are diagrams showing the structure and manufacturing method of semiconductor lasers according to the first to third embodiments of the present invention. In each figure, (d) is a cross-sectional view of the semiconductor laser, and (a)
) to (C) are diagrams illustrating the manufacturing method. 1 in the diagram
is n-GaAs substrate, 2 is n-A (L3Gao, 7A
s buffer layer, 3 is non-doped AA! o, IGa□, g
As active layer, 4 is I'-A"0.3o"0.7" cladding layer, 5 is p-GaAs cap layer, 6 is p-side electrode, 7
ijn side electrode, 8 Fi groove, 9 FiSift film, 10 is flat part, 11, 12 I/i end face, 21 is n-InP substrate, 22 tl;t n-InP buffer layer, 23 is non-doped InGaAsP active layer, 24 is p-InP cladding layer, 25 is p+-InGaAsP cap layer, 26 is bud.

Claims (1)

[Claims] forming a multilayer stacked structure including at least an active layer;
forming a plurality of grooves in the multilayer stacked structure that are deeper than the active layer and having side surfaces perpendicular to the active layer; and forming a dielectric film to cover at least the side surfaces of the grooves. . A method of manufacturing a semiconductor laser, comprising at least the steps of cutting the multilayer structure semiconductor wafer at the groove portion.