JPS6290969A - Manufacture of optical integrated circuit - Google Patents

Abstract

PURPOSE:To eliminate the influence of thermal damage by forming a protective layer of specific band gap wavelength on an active layer, removing the protective layer of an optical guide and the active layer, melting back the protective layer, and growing an intermediate layer. CONSTITUTION:A Te-doped N<+> type InP buffer layer 2, an InGaAsP active layer 3, and an InGaAsP or InGaAs protective layer 10 of lambdag=1.5-1.7mum are sequentially epitaxially grown on an S-doped N<+> type InP substrate 1. Then, with a laser A as a mask the layer 10 of an optical guide and the layer 3 are removed. The protective layer is melt back by the second epitaxial growth with the substrate, and a Zn-doped P<-> type intermediate layer 9, Zn-doped P<-> type InGaAs optical guide layer 6, a Zn-doped P<+> type InP clad layer 4, a Zn-doped P<+> type InGaAsP layer are sequentially grown. Thus, since the layer 3 is covered with the layer 10 at soaking time at high temperature in case of second LPE grown, no defect occurs in the boundary of the active layers.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an integrated external cavity laser (MEC-LD).
The present invention relates to a method of manufacturing an optical integrated circuit (semiconductor laser integrated with an optical waveguide), which is the basic structure of a semiconductor laser integrated with a monolithic optical switch, etc.

Conventional technology The technology for chemically coupling an optical waveguide and a semiconductor laser on the same substrate is the above-mentioned Ml! :C-LD or DBR-LD
Furthermore, it is indispensable for the formation of optical integrated circuits such as semiconductor lasers integrated with monolithic optical switches. Until now, this coupling technology has been advanced mainly in the development of DBR-LD. Among these, Bun published by Tokyo Tech in 1986
die -Integrated -Guide (
The DBR-LD (BIG) type has a planar structure and can achieve a coupling efficiency of 97% under optimal conditions, making it the most promising structure compared to other structures. A cross-sectional view of the structure of this element is shown in FIG. Here 1 is S-doped n+
-InP substrate, 2 is Te-doped n+-InP buffer layer, 3 is InG2LAsP active layer with λg = 1.3μ @,
4 is a Zn-doped p-InP cladding layer, 6 is a Zn-doped p-InGlLAsP:17 tact layer, and 6 is a Zn-doped p-InGa with λg=1.1 fi@.
AsP ml contact layer, plus 9 Zn-doped p
--InP intermediate layer.

The feature of this structure is that a thin p--InP intermediate layer 9 exists between the active layer 3 and the optical waveguide layer 6 in the Japanese laser, and the optical waveguide layer 6 and the p-InP cladding layer 4 are in the Japanese laser and the optical waveguide B. This is Hiroshi, who is a common layer. A method for manufacturing this structure using the liquid phase epitaxy method (LPIC method) is shown in FIG. First, as the first growth, an S-doped n-InP substrate 1
Above is a To-doped n+-InP buffer layer 2, λg=1.
3 μm InGamsP active layer 3 with a film thickness of 0.16 μm
1 more. , Zn-doped p-In with a film thickness of 1 μm
P grows to the intermediate layer (Figure 3 (2L)). Next, the intermediate layer 9 and active layer 3 are removed using a selective etchant using a laser mask (FIG. 3(b)). After removing the mask, Zn with λg = 1.1 μm was grown for the second time.
Doped p-InGaAsP optical waveguide layer 6 (film thickness 0.3μ
m), Zn-doped p-InP cladding layer 4, λg=
A 1.1 μm InG & Human SP:I77 tact was sequentially grown (Figure 3(C)). In this way, the surface can be almost completely flattened (planar structure), and subsequent processes such as buried epitaxial growth, other current confinement, three-dimensional confinement of light, and electrode formation and wiring are extremely difficult. can be easily carried out. Also in this case.

The coupling efficiency between the Japanese laser and the optical waveguide section B was as high as 97%, and the loss at the coupling section was almost negligible.

Problems to be Solved by the Invention However, in this manufacturing method, I
The nP intermediate layer 9 is exposed and is susceptible to thermal damage. This is because P easily dissociates at high temperatures of 650°C or higher (many gas bits are formed in InP, and the depth of these pits is several microns.rnP cover and P
Although the introduction of H can suppress this thermal damage, it does not essentially solve it. There is also a method of preventing heat damage by using a Ga-MuS cover, but in this case, an altered layer is formed on the surface. In this structure, the InP intermediate layer must be 0.1 μm or less, so such InP O
The influence of thermal damage extends to the InP intermediate layer/InG&MusP active layer interface, resulting in a decrease in luminous efficiency due to the introduction of defects.
This will adversely affect the characteristics of the laser, such as an increase in the threshold value.

As described above, the conventional manufacturing method of the BIG structure has the problem that it is difficult to obtain an element with good LD characteristics.

Means for Solving the Problems The present invention aims to overcome the above-mentioned problems by forming an InGaAsP layer with a bandgap wavelength λg of 1.5 μm to 1.7 μm on the InGaAsP active layer in the first epitaxial growth.
Or, after forming an InGaAs protective layer and removing the protective layer and active layer of the leading waveguide, the protective layer is selectively melted back in the second liquid phase epitaxial growth, and InP or a transparent layer to laser light is grown. InGaAs P interlayer of composition, also transparent InGa
This is a manufacturing method in which a Mu-sP optical waveguide layer, an InP cladding layer, and an rnGa-mu SP contact layer are sequentially grown.

Effect: By the means described above, it is possible to easily obtain an optical integrated circuit (semiconductor laser integrated with a guided waveguide) having good LD characteristics without being affected by thermal damage at high temperatures before the second growth.

EXAMPLE Below, a method for manufacturing a semiconductor laser having a BI structure in an example of the present invention will be described. FIG. 1 is a process diagram showing this manufacturing method. First, Te Doped n+-InP buffer layer 2 with a thickness of 5 μm
, the InGaAsP active layer 3 with λg=1.3 μm was formed with a thickness of 0.0 μm.
1s μ71. InGaAs protective layer 1o 023m
are sequentially grown epitaxially using a liquid phase or vapor phase growth method (Fig. 1('a-)). Next, the laser beam is masked and the InGaAa protective layer 10, In(rl
LAsP active layer 3 is removed using a selective etchant (first
Figure (b)). Using this epitaxial substrate having minute steps, a Zn-doped p-InP intermediate layer 9 was grown to a thickness of 0.1 μm in a second epitaxial growth.

Zn-doped p-InGaA with λg = 1.1 μm
sP optical waveguide layer 6, Zn-doped p-InP cladding layer 4
2 μ@, Zn-doped p-InGaAsP layer 0.5
711 is grown sequentially by liquid phase growth method (Fig. 1(C)
).

The InGaAs protective layer 10 is instantaneously melted back and removed when the p--InP intermediate layer 9 is grown.

This InGaAs protective layer 1o is made of InG having a composition of 1.7 μm ≧λg≧1.5 μm instead of InGaAs.
aAsP may also be used. In addition, the p-InP intermediate layer 9
For example, InGaLASP with 1.1 μm≧λg≧0.92 μm may be used instead of InP.

The device fabricated using this manufacturing method is made of InGaAsPnGaAs during the high temperature soak during the second LPE growth.
Since the protective layer 3s is covered with the protective layer 10, defects will not be introduced to the active layer interface and reduce the luminous efficiency of the semiconductor laser. This is because unlike InP, InGaA
Near the InGaAsP structure length temperature where s and λg are large (
This is because there is almost no thermal damage at temperatures of 650 to 670°C. As described above, the BIG structure optical integrated circuit manufactured by the manufacturing method of this example exhibits good laser characteristics, has a planar structure, and can have high coupling efficiency.

In this example, an n-type substrate was used, but a p-type substrate was used.
The same applies when a mold substrate is used. InG still in active layer
The composition of aAsP is also not limited to 1.3 μm.

Effects of the Invention As described above, in the present invention, the laser section is made of an InP substrate, an InP substrate, and an InP substrate.
Pn flange 2 fluff layer, InGaAs P optical waveguide layer, InP cladding layer,
When manufacturing an optical integrated circuit composed of an InGaAs P contact layer and an optical waveguide section composed of an InP substrate, an InP buff 77 layer, an InGaAs P optical waveguide layer, an InP cladding layer, and an InGaAs P contact layer, the first By growing a buffer layer and an active layer on the substrate, a further 2 μm1
, 5-1.7 μm InGamusP or InCa
After growing the As protective layer, the protective layer and active layer in the optical waveguide are removed, the protective layer is melted back in the second growth, and the guiding wave layer, cladding layer, and contact layer are sequentially grown. As a result, it is possible to obtain an optical integrated circuit that exhibits good semiconductor laser characteristics with no defects introduced at the active layer interface and has a planar structure with high coupling efficiency, and various devices based on this can have long-lasting characteristics. can be obtained.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing a method for manufacturing a Bl(, structured MEC laser) according to an embodiment of the present invention, and FIG.
FIG. 3 is a cross-sectional structural diagram of a structured MEC laser, and is a process diagram showing a method of manufacturing the conventional laser. 1.=-S-doped n-InP substrate, 3-.=InG
aAsP active layer, 6 --- --- Z n-doped p
-InGaASP optical waveguide layer, 9...Zn-doped p--InP intermediate layer, 10...InGaAs
Protective layer, A: laser section, B: optical waveguide section. Name of agent: Patent attorney Toshio Nakao and 1 other person i1
Figure (cL) Figure 2

Claims (1)

[Claims] One element monolithically has a laser section and an optical waveguide section, and the laser section is made of an InP substrate, an InGaAsP active layer, an InP or InGaAsP intermediate layer, an InGaAs
The optical waveguide is composed of an optical waveguide layer, an InP cladding layer, and an InGaAsP contact layer.
nGaAsP optical waveguide layer, the InP cladding layer, the I
When manufacturing an optical integrated circuit having a structure composed of an nGaAsP contact layer, the InGaAsP layer is first grown on the InP substrate by liquid phase or vapor phase epitaxial growth.
The active layer further has a bandgap wavelength (λg) of 1.5~
After forming a 1.7 μm InGaAsP or InGaAs protective layer and selectively removing the protective layer and the active layer of the optical waveguide, the InP or InGaAs intermediate layer is grown by a liquid phase epitaxial growth method using a melt. The protective layer is selectively melted back, the intermediate layer is formed, and the InGaAs
P optical waveguide layer, the InP cladding layer, the InGaAs
A method for manufacturing an optical integrated circuit, comprising sequentially forming P contact layers.