JPH01189185A - Manufacture of semiconductor laser having embedded structure - Google Patents

Abstract

PURPOSE:To eliminate abnormal growing in the vicinity of a mesa, to omit restriction on embedded growing due to the height of the mesa and to enhance reliability, by using dry etching when the mesa structure is formed. CONSTITUTION:An Se doped type InP buffer layer 1b, an undoped GaInAsP active layer 2 and a P-type GaInAsP cap layer 7 are grown on a (100)-face N-type InP substrate 1a. Then, a titanium oxide film 8 is attached. The stripe mask of the titanium oxide film is formed in the orientation of (011). A mesa structure is formed by using an argon-chloride based RIE device. Then, a P-type InP current blocking layer 4 and an N-type InP current blocking layer 5 are formed so as to embed a region other than the mesa structure selectively. The titanium 8 is removed. An electrode comprising Au/Zn/Ni is evaporated on the growing side and an electrode comprising Au/Ge/Ni is evaporated on the substrate side in a vacuum state. Since the dry etching is used in this way, a (111) face does not appear on the surface of the mesa side, and the restriction caused by the height of the mesa is not imposed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a buried structure semiconductor laser using an organometallic epitaxial method capable of growing an epitaxial film having a uniform composition and layer thickness over a large area. be.

[Conventional technology]

It is desirable that the laser oscillates at a low threshold and operates in a stable mode. As a device that satisfies these conditions, there is a buried structure semiconductor laser in which the active layer is surrounded by a material having a lower refractive index than the active layer.

FIG. 8 shows a typical structure of a buried structure semiconductor laser that has been reported so far.

Figure 8 is the one reported by M, Hirao et al. (J, Apprho, phys, 19
80. vol, 51. P453'9). In the figure, 1b is an n-type 1nP buffer layer, 2 is a GaInAsP active layer, 3 is a p-type InP cladding layer, 4 is a p-type InP current blocking layer, 5 is an n-type 1nP current confinement layer, and 7 is a p-type Ga1nAsP cap layer. be. The active layer 2 has a buried structure surrounded by an InP layer lb, 3.4.5 having a low refractive index. In this structure, block layer 4
The current confinement layer 5 is formed by liquid phase epitaxial method (LPE).
The LPE method takes advantage of the fact that crystals do not grow on the dielectric film attached to the top of the mesa.

[Method to solve the problem]

However, metal organic vapor phase epitaxial method (MOVPE)
When embedding an inverted mesa structure having a height of more than .mu.m with the Sing film 8 on the top surface of the mesa shown in FIG. 9 using the method shown in FIG. This is thought to be due to the presence of (111) planes on the sides of the mesa where epitaxial growth is difficult to occur. In order to perform buried growth to prevent abnormal growth on the mesa sides, the mesa sides are selectively buried using a mask on the top of the mesa in an inverted mesa structure with a mesa height of 1 μm or less, and after the mask is removed, the substrate Two steps are required to grow the entire surface. This can be seen, for example, in ``Kondo et al.
It is described in the 2018 Spring Science Proceedings 30P-ZH-8J.

For this reason, when manufacturing a buried structure laser using the conventional MOVPE method, it is necessary to control the mesa height to 1 μm or less, and it is quite difficult to uniformly perform this by wet etching. In addition, when a buried structure laser is manufactured in this way, the (111) plane, which is difficult for epitaxial growth to occur, appears on the side surface of the mesa, and as shown in Figure 10, growth does not proceed at the interface with the buried layer, resulting in a crystalline structure. This may cause problems with the reliability of the laser.

[Means to solve the problem]

The purpose of the present invention is to eliminate abnormal growth near the mesa caused by gas transport development peculiar to vapor phase growth, eliminate the limitation on buried growth due to mesa height, and provide a method for manufacturing a buried structure semiconductor laser with high reliability. Our goal is to provide the following.

The present invention involves selectively etching a first conductivity type semiconductor substrate having a multilayer structure including a first conductivity type buffer layer, an active layer, a second conductivity type cladding layer, or a second conductivity type cap layer. The main feature is that when forming the structure, dry etching is used instead of wet etching used in conventional techniques. By using dry etching, the (111) surface does not appear on the mesa side. It is possible to easily and uniformly form a nearly vertical mesa structure.

As a result, even when the mesa height is 2 μm or more,
It is possible to suppress abnormal growth in the vicinity of the mesa and embed the mesa flatly, and since the crystallinity on the side surfaces of the mesa is improved, defects at the interface are reduced and reliability is improved.

〔Example〕

1 to 3 show a method for manufacturing a semiconductor laser according to the present invention in order. First, as shown in Figure 1, (10
0) Se-doped n-type 1nP buffer layer 1b (d! 24m) on surface n-type 1nP substrate la, undoped GaInAs
P active layer 2 (d=Q.

1 μm), p-type InP cladding layer 3 (d=1.0μ
m), p-type Ga1nAsP cap layer? (d=0.5
μm) is grown by the MOVPE method.

Next, in FIG. 2, a titanium oxide film 8 is attached to the growth surface by sputtering method, and (0
11) Form a titanium oxide film stripe mask with a stripe width of approximately 1.5 μm in the direction.

Then, a mesa structure with a mesa height of 2.0 μm is formed using a chlorine-argon RIE device. At this time, the mesa side surface is at about 80 degrees with respect to the substrate surface, and the (111) plane is not exposed. Also, since it is almost vertical, the cladding layer 3 is 1μ
Even when the active layer width is about 2 μm, the active layer width is 2 μm or less,
Control of transverse mode is possible. Furthermore, due to the characteristics of dry etching, the mesa height can be formed uniformly within the surface.

Next, as shown in FIG. 3, a p-type InP current blocking layer 4 (d=l μ
m), n-type! An nP current confinement layer 5 (d: 1 μm) is formed. In this case, the MOVPE growth conditions include, for example, PH, :TMI-150:1 as the source gas.
DEZ is used as a doping gas when depositing P-type 1nP, H and Se are used as doping gases when depositing n-type 1nP, and hydrogen is used as a carrier gas. 50T0rr,
Deposition is performed at a substrate temperature of approximately 685°C.

In this growth, the mesa height is 1 μm or more, but no angular abnormal growth occurs on the sides of the mesa.

Next, the titanium oxide 8 on the upper surface of the mesa is removed using HF. Then, polish the substrate side to reduce the thickness of the wafer to approximately 80 μm.
After that, A u /Z n /Ni electrode was placed on the growth side,
Au/Ge/Ni electrodes are vacuum-deposited on the substrate side and heat treated in H2 at 420°C to form electrodes. Thereafter, the plane parallel to the plane of the paper is separated to produce a laser chip.

As shown above, if a laser device is manufactured by using dry etching to form a mesa structure, the (111) plane will not appear on the mesa side surface, so the MOVPE method can be used without being limited by the mesa height. The mesa can be buried flat without causing abnormal growth in the vicinity of the mesa, and a buried structure semiconductor laser can be easily manufactured using only the MOVPE method. Furthermore, by wet etching the side surfaces of the mesa before growth to remove areas damaged by dry etching, the interface condition can be improved and reliability can be improved.

Furthermore, in the above example, a buried structure laser device was fabricated by one-time buried growth using the MOVPE method, but as in the conventional method, a mesa structure with a low mesa height was used, and growth was selectively performed in areas other than that area. A buried structure laser may be manufactured by two-time MOVPE buried growth in which the mask is removed and growth is performed on the entire surface of the substrate. The process is shown in FIGS. 4 to 7. In addition, in this case, if n-type InP is used for the part that becomes the buried layer 6, Z
What is necessary is to perform n diffusion to make the p-type.

Furthermore, a Se-doped n-type InP layer 1 is used as the semiconductor substrate 1.
An n-type 1nP substrate 1a without b may also be used.

Furthermore, in the above embodiment, as the current block section, In
Although a pn reverse bias layer of P is used, a semi-insulating InP layer may be used instead of the p-type InP current blocking layer 4 and the n-type 1nP current confinement layer N5.

Furthermore, although we have described the GaInAsP/InP system,
Other crystal systems such as the GaAs/ARGaAs system may also be used.

Furthermore, although the explanation has been made using an n-type substrate, the same thing can be done using a p-type substrate.

〔Effect of the invention〕

As explained above, the present invention has a method for forming mesa on the side faces (11
1) By using dry etching that does not expose the surface, buried growth is possible without abnormal growth near the mesa, regardless of the mesa height, and the crystallinity of the mesa side surface is improved, improving the characteristics of laser denomination. increase. Furthermore, by using dry etching, which enables uniform etching, it is possible to make use of the advantage of the MOVPE method, which allows growth over a large area at one time, to make it possible to fabricate a large number of semiconductor laser devices. Further, since a uniform mesa can be formed, laser characteristics such as a narrow line width can be obtained and the laser characteristics can be improved.

In the present invention, unlike the buried structure laser using the conventional MOVPE method, the invention as claimed in claim 1 requires only one buried growth, which simplifies the manufacturing process.

Similarly, the invention described in item 2 requires buried growth twice, but it improves crystallinity on the mesa side surface more than the invention described in item 1, and further improves characteristics such as reliability. Similarly, the invention in item 3, compared to the inventions in items 1 and 2, is a high resistance Invention.
Since it is buried with a P layer, it is possible to stop current confinement to the active layer, and by eliminating the pn junction used as a current blocking part in the inventions of Items 1 and 2, It is possible to reduce the parasitic capacitance of the laser element and improve high frequency characteristics.

[Brief explanation of the drawing]

1 to 3 are process cross-sectional views for explaining one embodiment of the method for manufacturing a buried structure semiconductor laser device according to the present invention, and FIGS. 4 to 7 are for explaining a second embodiment thereof. Figure 8 is a cross-sectional view showing a conventional buried structure semiconductor laser fabricated by the LPE method, Figure 9, Figure 1.
FIG. 0 is a cross-sectional view for explaining a conventional manufacturing method using the MOVPE method. 1, la''-n type 1nP substrate, b...n type rnP buffer layer, 2...GaInAsP active layer, 3...p
TnP type cladding layer, 4...p type 1nP current blocking layer, 5...n type InP current confinement layer, 6...p type ■
nP buried layer, 7...p-type Ga1nAsP cap layer, 8...titanium oxide film Patent applicant Nippon Telegraph and Telephone Corporation agent Patent attorney Kugobe Tamamushi (2 others) Figure 1 Figure 2 Figure 2 3 Cross-sectional view of the second embodiment of the present invention 1 Figure 4 Wfri of the 12th embodiment of the present invention! Fig. 1 Fig. 5 A cross-sectional view of the second fruit of the present invention 6 Fig. 7 A cross-sectional view of the second fruit of the present invention Fig. 7 A cross-section of a semiconductor laser Fig. 8 A cross-sectional view of the second fruit of the present invention Cross-sectional view of the conventional manufacturing method Fig. 9 Cross-sectional view of the conventional manufacturing method according to MOVPE

Claims (3)

[Claims] (1) an active layer on a first conductivity type semiconductor substrate or a substrate having a first conductivity type buffer layer formed on the semiconductor substrate;
A step of depositing a second conductivity type cladding layer and a second conductivity type cap layer, and selectively etching the cap layer, the cladding layer, the active layer, the buffer layer, or the semiconductor substrate using dry etching to form a mesa. A step of forming a mesa structure whose side surfaces are at an angle close to perpendicular to the substrate surface at 90 degrees to 70 degrees and has a plane orientation different from the (111) plane, using a mask on the top surface of the mesa structure by an organometallic epitaxial method. A method for manufacturing a buried structure semiconductor laser, comprising the step of selectively growing a second conductivity type semiconductor layer and a first conductivity type semiconductor layer in a region other than the mesa structure. (2) a step of depositing an active layer and a second conductivity type cladding layer on a first conductivity type semiconductor substrate or a substrate having a first conductivity type buffer layer formed on the semiconductor substrate; and the cladding layer; The active layer, the buffer layer, or the semiconductor substrate is selectively etched using dry etching so that the mesa side surface forms a nearly perpendicular angle of 90 degrees to 70 degrees with the substrate surface (1
11) A step of forming a mesa structure having a plane orientation different from that of the plane, and selectively forming a second layer in a region other than the mesa structure using a mask on the top surface of the mesa structure by an organometallic epitaxial method.
A step of growing a conductive type semiconductor layer, a first conductive type semiconductor layer, and a step of removing a mask on the top surface of the mesa structure and growing a second conductive type semiconductor layer, a second conductive type cap layer on the entire surface of the substrate. A method for manufacturing a featured buried structure semiconductor laser. (3) an active layer on a first conductivity type semiconductor substrate or a substrate having a first conductivity type buffer layer formed on the semiconductor substrate;
depositing a second conductivity type cladding layer and a second conductivity type cap layer; selectively etching the cap layer, the cladding layer, the active layer, the buffer layer or the semiconductor substrate using dry etching; A process of forming a mesa structure in which the mesa side surface is at a near perpendicular angle of 90 degrees to 70 degrees with the substrate surface and has a plane orientation different from the (111) plane, using a mask on the top surface of the mesa structure by the organometallic epitaxial method. A method for manufacturing a buried structure semiconductor laser, comprising the step of selectively growing a semi-insulating semiconductor layer in a region other than a mesa structure.