JPH06132609A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a distributed feedback (DFB) type semiconductor laser from which the high monochromaticity of spectrum can be obtained and also to provide the manufacture thereof. CONSTITUTION:A process of forming semiconductor layer 14 for stopping etching, a semiconductor layer 15 for modulating a refractive index and a semiconductor layer 16 for transferring a pattern on a semiconductor multilayer film including an underlying cladding layer on a compound semiconductor substrate 11, an activated layer 13 and an upside cladding layer 12, a process of forming a diffraction grating on the layer 15 for modulating a refractive index and a process of burying the semiconductor layer 15 for modulating a refractive index in which a diffraction grating is formed and the semiconductor layer 16 for transferring a pattern with a semiconductor layer 18 are provided. Thereby, the patterns of diffraction grating are formed to make a semiconductor laser device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed feedback (DFB) semiconductor laser device which can obtain high monochromaticity of a spectrum and a manufacturing method thereof.

[0002]

2. Description of the Related Art In manufacturing a distributed feedback semiconductor laser having a diffraction grating (hereinafter abbreviated as "DFB laser"), a photoresist is formed on a semiconductor substrate or a guide layer grown on the semiconductor substrate, and interference exposure is performed. After the diffraction grating pattern is formed on the resist by using the method or electron beam exposure method, the diffraction grating is transferred and formed on the semiconductor guide layer by wet etching with a chemical solution or dry etching with a reactive gas.

[0003]

However, although dry etching is superior to wet etching in controllability and uniformity, it is possible to obtain a diffraction grating having a uniform grating shape over a wide area with good reproducibility regardless of which etching method is used. It was difficult to form. In particular, when the diffraction grating is filled with a semiconductor layer, the shape of the diffraction grating is slightly deformed due to crystal growth, so that it is difficult to accurately control the coupling efficiency based on the shape. The present invention is DFB
An object of the present invention is to provide a semiconductor laser device which can form a laser diffraction grating with high precision and can remarkably improve the spectral characteristics of the laser, and a manufacturing method thereof.

[0004]

The structure of a semiconductor laser device according to the present invention for achieving the above object is a semiconductor laser device comprising a semiconductor multilayer film in which an active layer formed on a compound semiconductor substrate is sandwiched by cladding layers. A semiconductor pattern transfer layer, a semiconductor refractive index modulation layer, and a semiconductor etching stop layer are provided adjacent to the guide layer, the refractive index modulation layer has a diffraction grating, and the semiconductor multilayer film layer is embedded. And

The first aspect of the present invention for manufacturing the same
In the method for manufacturing a semiconductor laser device, a compound semiconductor substrate is provided with a semiconductor clad layer, an active clad layer and a semiconductor multilayer film including an upper clad layer, a semiconductor etching stop layer,
Forming a semiconductor refractive index modulation layer and a semiconductor pattern transfer layer, forming a diffraction grating in the semiconductor pattern transfer layer, forming a diffraction grating in the semiconductor refractive index modulation layer, and forming the diffraction grating And a step of filling the semiconductor refractive index modulation layer and the semiconductor pattern transfer layer with a semiconductor layer.

The second method of manufacturing a semiconductor laser device includes a step of forming a semiconductor refractive index modulation layer and a semiconductor pattern transfer layer on a compound semiconductor substrate, and a step of forming a diffraction grating in the semiconductor pattern transfer layer. A step of forming a diffraction grating in the semiconductor refractive index modulation layer, a step of embedding the semiconductor refractive index modulation layer in which the diffraction grating is formed and the semiconductor pattern transfer layer with a semiconductor layer, a lower clad layer, an active layer and an upper clad And a step of forming a semiconductor multilayer film including layers.

[0007]

According to the present invention, by providing a semiconductor pattern transfer layer, a semiconductor refractive index modulation layer and a semiconductor etching stop layer having different compositions formed on a semiconductor substrate, a fine diffraction grating pattern can be selectively etched in a semiconductor thin film. To achieve a semiconductor laser with excellent wavelength characteristics, which has a high etching controllability and can form a diffraction grating pattern in the shape as designed because the etching is completed in the semiconductor etching stop layer. You can

[0008]

EXAMPLES The present invention will be described in detail below based on examples.

Embodiment 1 FIG. 1 shows a first embodiment of the present invention. Here, a procedure for manufacturing a long wavelength band DFB laser using InP as a substrate will be described, but a DFB laser can be manufactured by the same method in the case of a short wavelength band using GaAs as a substrate.

First, the InP substrate 11 is set as a semiconductor substrate in the substrate holder in the ultra-high vacuum apparatus, and the temperature is about 450.degree.
To about 550 ° C. After that, triethylindium (TEIn), triethylgallium (TEGa),
A semiconductor raw material such as arsine (AsH3) or phosphine (PH3) is supplied, and the following semiconductor multilayer film is formed by a molecular beam epitaxy method using an organometallic gas.

As shown in FIG. 1A, on the InP substrate 1
InGaAsP optical guide layer 12 as the lower clad layer, InGaAsP active layer 13 and InGaAsP optical guide layer 12 as the upper clad layer are quasi-formed in 1 and then the InP etching stop layer 14 and InGaAsP A semiconductor multilayer film of the refractive index modulation layer 15 and the semiconductor pattern transfer layer 16 of InP is formed. Here, as the active layer 13 of InGaAsP, an active layer having a quantum well structure of a multi-element mixed crystal is used, and specifically, the barrier layer 1 made of In _x Ga _1-x As _1-y P _y.
00Å and a well layer 40Å made of In _x Ga _1-x As
And were alternately laminated in 4 to 6 layers.

Next, as shown in FIG. 1B, a photoresist thin film is formed on the uppermost InP pattern transfer layer 16, and then a diffraction grating having a predetermined grating interval is formed by an interference exposure method or an electron beam drawing method. The pattern 17 is formed.

Next, as shown in FIG. 1C, a diffraction grating is formed on the InP pattern transfer layer 16 using a hydrochloric acid-based etching solution with the diffraction grating pattern 17 of this resist as an etching mask. Then, the resist is removed.

Next, as shown in FIG. 1D, a diffraction grating is formed on the refractive index modulation layer 15 by using a sulfuric acid type etching solution with the pattern transfer layer 16 as an etching mask. In these etching processes, the film thickness is 50Å-10
Since selective etching is performed with semiconductor thin films having different compositions of about 0Å, and an etching stop layer is formed on each, a highly accurate diffraction grating can be produced with good reproducibility.

After the diffraction grating of the refractive index modulation layer 15 can be formed on the etching stop layer 14, a semiconductor crystal thin film is grown again by the molecular beam epitaxy method using an organic metal gas. That is, as shown in FIG.
A cladding layer 18 made of InP and a contact layer 19 made of InGaAsP are formed.

Through the above steps, a DFB laser structure having a diffraction grating embedded therein can be realized. A DFB laser in which the active layer has a ridge structure or a current confinement region is embedded can be realized by a conventional technique using this substrate.

Embodiment 2 FIG. 2 shows a second embodiment of the present invention. The manufacturing process is basically the same as that of the first embodiment, but here, the diffraction grating is formed on the InP substrate 11 side and embedded.

As shown in FIG. 2A, I is deposited on the InP substrate 11 by the molecular beam epitaxy method using an organometallic gas.
A semiconductor thin film of a refractive index modulation layer 15 made of nGaAsP and a pattern transfer layer 16 made of InP is grown. Here, as the etching stop layer, the InP substrate 11 is used.
Have that function.

Next, as shown in FIG. 2B, after forming a diffraction grating pattern 17 on the photoresist, using this as an etching mask, a hydrochloric acid type etching solution is used,
As shown in FIG. 2C, a diffraction grating pattern is formed on the InP pattern transfer layer 16. Further, as shown in FIG. 2D, a diffraction grating is formed on the refractive index modulation layer 15 using the pattern transfer layer 16 as an etching mask and using a sulfuric acid-based etching solution.

Then, as shown in FIG.
After the refractive index modulation layer 15 in which the diffraction grating is formed is embedded with InP by the molecular beam epitaxy method using an organic metal gas, the InGaAsP guide layer 12 and InGaAsP are formed.
The semiconductor thin film layers of the active layer 13, the guide layer 12, the cladding layer 18, and the contact layer 19 having the quantum well structure of P multi-element mixed crystal are crystal-grown to realize the DFB laser structure. Similar to the first embodiment, a DFB laser in which the active layer has a ridge structure or the current confinement region is buried can be realized by the conventional technique using this substrate.

The refractive index modulation layer 15 of the present invention can function even if it has the same composition as the guide layer, but it may have a desired composition in consideration of the change in refractive index and the height of the diffraction grating. Further, the InP pattern transfer layer 16 also has a function of suppressing deformation of the refractive index modulation layer 15 at the time of embedded growth.

Although the present invention has been described above based on the embodiments, in the case of the upper type in which the diffraction grating is formed on the active layer of the first embodiment, the composition and the film thickness of the semiconductor multilayer film after the crystal growth are changed. There is an advantage that a diffraction grating can be manufactured.
On the other hand, in the case of the lower type in which the diffraction grating is formed in advance on the substrate of Example 2, the semiconductor multilayer film must be formed in the subsequent crystal growth step so as to match the characteristics of the diffraction grating. Therefore, a crystal growth technique with high controllability is required.

[0023]

According to the present invention, the controllability and uniformity of the diffraction grating are dramatically improved, and in particular, the long resonator in which the uniformity within the resonator of the diffraction grating affects the unity of the spectrum. It is possible to remarkably improve the spectral line width of a distributed feedback (DFB) semiconductor laser of the type. Therefore, the present invention is the core of the basic technology for improving the DFB laser characteristics in the future, and is expected to make a great contribution to the development of the system by improving the device characteristics.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a manufacturing method according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a manufacturing method according to a second embodiment of the present invention.

[Explanation of symbols]

 11 InP Substrate 12 Optical Guide Layer (InGaAsP) 13 Active Layer (InGaAsP) 14 Etching Stop Layer (InP) 15 Refractive Index Modulating Layer (InGaAsP) 16 Pattern Transfer Layer (InP) 17 Diffraction Grating Pattern 18 Cladding Layer (InP) 19 Contact Layer (InGaAsP)

Claims (3)

[Claims] 1. A semiconductor laser device comprising a semiconductor multilayer film in which an active layer formed on a compound semiconductor substrate is sandwiched by cladding layers, and a semiconductor pattern transfer layer, a semiconductor refractive index modulation layer, and a semiconductor etching stop are adjacent to a guide layer. A semiconductor laser device, wherein a layer is provided, the refractive index modulation layer has a diffraction grating, and the semiconductor multilayer film layer is embedded. 2. A lower clad layer on a compound semiconductor substrate,
On the semiconductor multilayer film composed of the active layer and the upper clad layer,
A step of forming a semiconductor etching stop layer, a semiconductor refractive index modulation layer, and a semiconductor pattern transfer layer; a step of forming a diffraction grating in the semiconductor pattern transfer layer; and a step of forming a diffraction grating in the semiconductor refractive index modulation layer, And a step of embedding the semiconductor refractive index modulation layer having the diffraction grating and the semiconductor pattern transfer layer with a semiconductor layer. 3. A step of forming a semiconductor refractive index modulation layer and a semiconductor pattern transfer layer on a compound semiconductor substrate, a step of forming a diffraction grating in the semiconductor pattern transfer layer, and a diffraction grating in the semiconductor refractive index modulation layer. A step of forming, a step of embedding the semiconductor refractive index modulation layer having the diffraction grating formed therein and the semiconductor pattern transfer layer with a semiconductor layer, and a step of forming a semiconductor multilayer film layer including a lower clad layer, an active layer and an upper clad layer A method for manufacturing a semiconductor laser device, comprising: