JPS58137283A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To form a crystal grown layer with excellent reproducibility by forming a groove with a flat bottom onto a substrate and using the groove as a nucleus for crystal growth. CONSTITUTION:Grooves 22, 23 are formed in parallel onto the N-GaAs substrate 21. An N-GaAlAs layer 24, a P-GaAs layer 25 and a P-GaAlAs layer 26 are grown onto the substrate 21 in succession by using a liquid epitaxial crystal growth method, and a double hetero-junction layer 27 is formed. An N-GaAlAs layer 28 is crystal-grown while a SiO2 film 29 is formed onto the layer 28. The built-in guide type laser is obtained by forming electrodes 30, 31 and a diffusion layer 32.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for manufacturing a semiconductor laser having a built-in waveguide structure [Technical Background of the Invention and Problems thereof] A semiconductor laser as a light source for an optical disk. In view of this, it is desirable that the laser structure is built-in in the form of a waveguide. The built-in structure is the simplest as a waveguide laser.
A channeled substrate planar (CEP) laser is known, which is manufactured by forming a V-shaped groove on a semiconductor substrate and performing two-way crystal growth.

The thirteenth figure is a schematic structure of a conventional G1JA-based CSP laser. A double heterojunction (DH) junction layer S is grown.

A current narrowing layer 1 and an insulating layer 8 are formed on the DH junction layer σ. In the figure, 9.10 is an electrode, and 11 is a diffusion layer [indicated at 0]. In such a C8P laser, when considering the waveguide mode t in the direction perpendicular to the bonding surface, there is a waveguide outside the V-shaped groove 2. The wave path light permeates to the substrate crystal 1, where the absorption loss of the substrate crystal 1 with a narrow bandgap [feels 0].
Message mode horizontally on the joint surface [When thinking 9 times, V-shaped groove 2
There is a large difference in loss (difference in gain) between the inside and outside of the joint, and this difference also causes a V
The effect of confining light in the groove 2 occurs. Since the difference in gain or loss caused by the presence of the V-groove 2 is created as a crystal, unlike a so-called gain waveguide laser, stable transverse mode control is possible even in the direction horizontal to the junction surface. You can expect good results.

By the way, in order to realize the above-mentioned transverse mode control effect with the C8P laser, it is necessary to make sure that the mode sufficiently oozes out from the substrate crystal 1t in the outer part of the V-shaped groove 2. Therefore, the thickness of the active layer 4 and the thickness of the cladding layer between the active layer 4 and the substrate 1 must be extremely thin, 1 degree or less. At present, the liquid phase epitaxial crystal growth method (LPIC method) is normally used for crystal growth, which is the ninth step in manufacturing C8P lasers. Crystal growth [Good control] is not easy to perform.Especially in CAP lasers, grooves are formed in the substrate crystal, and the shape of these grooves is the melt of the crystal growth.

To prevent melting and deformation due to a phenomenon called dopatsuku,
When it is necessary to grow crystals under conditions of high supersaturation, it is extremely difficult to achieve well-controlled crystal growth of the thin film.

Recently, a twin mesa substrate (TMS) laser, as shown in Figure 2, has been developed to solve the above problems in CSP lasers. ◇In the case of this laser, it plays the same role as the C8P laser. The V-shaped groove 2 is formed on the diagonal convex portion 12 of the substrate crystal 1. This is because in the LPE method, the crystal formation rate of the Methi convex portion 12 is slowed down, and it becomes easy to grow the thickness of the cladding layer 3 and the thickness of the active layer 4 at the outer part of the V-shaped groove 2 to be thinner. . The reason why the growth of the methi convex portion 12 is slow is as follows.
When crystal growth is carried out under conditions close to the equilibrium state with low supersaturation, it is difficult to generate crystal growth nuclei on the top surface of the mesa, whereas at the bottom of the mesa, the concave area formed by the mesa bottom and mesa glue surface facilitates crystal growth. Role as a nucleus [This is because the pericarp is denser, and as a result, crystal growth is faster at the bottom of the pericarp. Therefore, even if the crystal growth is performed under conditions of high supersaturation so that the V-shaped groove 2 is not deformed due to meltback, it is possible to prevent the crystal growth layer from becoming thicker in the upper part of the mesa.

However, such a 7MS laser has the following problems: The crystal growth layer on the top surface of the mesa [although it is easy to make it thin, it is difficult to accurately control the thickness of the layer] It is difficult. The reason for this is that there is no particular place on the top surface of the mesa that serves as a crystal growth nucleus like the bottom of the mesa, and the degree of edge growth is not constant. For example, the influence of edge growth from an abnormally grown layer that often occurs at the edge of a wafer may affect the edge growth state. . This method made it difficult to manufacture semiconductor lasers with good reproducibility.
[Object of the Invention] An object of the present invention is to provide a semiconductor laser that can form a desired crystal growth layer with good reproducibility and improve manufacturing yield when manufacturing a semiconductor laser having a built-in waveguide structure. The purpose of this invention is to provide a method for manufacturing the same.

[Summary of the invention]

Does the present invention have a built-in waveguide structure? When manufacturing a semiconductor laser with a semiconductor laser, a first groove with a flat bottom is formed on the semiconductor substrate by selective etching, and a second groove is formed at the bottom of the first groove parallel to the groove. In this method, a Peter junction layer consisting of an active layer and a two-layer layer is formed on the semiconductor crystal substrate by a liquid phase epitaxial method.

〔Effect of the invention〕

According to the present invention, the first groove serves as a nucleus for crystal growth on a semiconductor substrate crystal, thereby eliminating uncertain factors in crystal growth and controlling the thickness of crystal growth. [Crystal growth can be determined by controllable factors such as supercooling of the melt and cooling rate. Therefore, the crystal growth layer can be formed with good reproducibility and the manufacturing yield can be improved. Manufacturing process mt - is a cross-sectional view showing 0 First, jI
As shown in Fig. 3-), N whose main surface is the (001) plane
- On the GaAm substrate (semiconductor substrate crystal) 21, a wide groove (III groove) 22 and a figure 7 groove ($12 groove)
23t each formed in parallel. The width of the groove 22 of JIll is 50 [μm], the depth is 2Cf1tt), and the 20th
The width of the grooves 23 is 3 (μl).
．． :! 3 was formed using a photoresist mask and an etchant with remarkable selectivity to the surface index of phosphoric acid dihydrogen peroxide: methanol = 1:1:3, and the etching was performed in the <01> direction. Next, using the LPE method, as shown in FIG. 93(b), the substrate 21 is
On top is a layer of N-G a L layer (2 layers) 24,
P-G a A 8 layer (active layer) 25 and P-G
The aAtAs layer (cladding layer) is grown to form a DH junction layer zv5. At this time, the second groove 23 is filled in the very early stage of crystal growth, and then the first groove z
Crystal growth also starts from the steps on both sides of the substrate crystal 21. The growth of the first layer of Is begins after slow cooling at a rate of 7 [°C/min].
9. Using a method of bringing the substrate into contact with the 1i melt and lowering the cooling rate to 1 by 0.2 (°C/min), the temperature of the substrate 21 is approximately 2 [°C].
The first layer of N-GaAtAs contacts the crystal growth melt under supercooled conditions, and under these conditions grooves are formed and the substrate 21 is hardly melted back.
The contact time of the active layer 25 is approximately 20 seconds. Even with this short contact, crystal growth proceeds until the second groove 23 is approximately flattened. In the case of growth of the zero-order active layer 25, Groove 2
The ribs on both sides of 2 play an important role [0 In other words, edge growth occurs from the walls on both sides, IJlt) @z
Every time you dig one by one from the bottom of the go, it becomes -. Since the edge growth generated from the wall surface of the groove 22 of o-JLa is created as a substrate, there are fewer uncertain factors compared to the case of crystal growth on a conventional substrate in which only a figure-7 groove is formed. Therefore, it is possible to form each crystal layer at the bottom of the Isl groove with good reproducibility. If it is, it is undesirable because it will be affected by edge growth from the walls on both sides of the groove 220. #
! It is better to form the second groove 23 on one side of the wall on either side of the first groove 22 to obtain a preferable result in terms of reproducibility. As shown in the same figure (C), N-GaAtA easy 7Hz m5 crystals were grown on the sample shown,
810 on the corpse layer 28! 29 films (insulating layers) are formed. Furthermore, by forming the electrodes 20, 31 and the diffusion layer 32, a built-in waveguide-shaped laser is realized.The semiconductor laser thus formed has good reproducibility in the thickness of the cladding layer 24 and the active layer 25. It has been confirmed that the manufacturing yield is high.

FIGS. 4(a) to 4(C) show a semiconductor laser manufacturing process 11 according to another embodiment. [It is a sectional view shown in FIG. This embodiment differs from the previously described embodiment in that the grooves 22 and 23f are formed above the mesa convex portion 4. In this case, there is a portion where crystal growth is likely to occur outside the mesa convex portion Therefore, the crystal growth rate in the vicinity of the second groove 23 can be made slower than in the previous embodiment. For this reason, the film thicknesses of the 2D layer 24 and the active layer 25 can be controlled more accurately.

be able to.

Note that the present invention is not limited to the embodiments described above, and can be implemented with various modifications without departing from the gist thereof. For example, the width, depth, etc. of the first and second grooves may be determined as appropriate according to specifications. In addition, not only GaAtAs-GaAg laser but also InG laser
Of course, it can also be applied to an aAsP-I IIP laser.

[Brief explanation of drawings]

93 (a) to (C) are cross-sectional views showing the manufacturing process of a semiconductor laser according to an embodiment of the present invention;
Figures F44-) to (c) are cross-sectional views showing the manufacturing process of a semiconductor laser according to another embodiment. 21...N-GaAs substrate (semiconductor substrate crystal), 22...first groove, 23...second groove, 24...
N-GaAjAs layer (cladding layer), ZS-...P-
-G a A a layer (active layer), 26 ・” P-Ga
AtAs layer (cladding layer), 27...double terror (DH) jealousy layer, 2 g-N-GaAtAs layer, 29
-810°all (insulating layer), 30.31...electrode,
32... Diffusion layer, 41... Mesa convex portion. 1. Applicant's agent Patent attorney Takeshi Suzue Disciple 1 Figure 3 (b) 1

Claims (1)

[Claims] (1) On the semiconductor substrate crystal [Selective etching is performed to form #It of III with a flat bottom on the substrate, and at the same time, a groove of Is2 is formed at the bottom of the groove of Jll in parallel with the groove. A method for manufacturing a semiconductor laser characterized by forming a heterojunction layer consisting of an active layer and a layer on a crystal substrate by liquid phase epitaxial method 0 (2)
) The ill groove is formed in a convex portion provided on the semiconductor crystal substrate.
A method for manufacturing a semiconductor laser according to item 1111.