JP2771276B2 - Semiconductor optical integrated device and manufacturing method thereof - Google Patents

Description

The present invention relates to the structure and manufacturing method of a semiconductor optical integrated device,
In particular, the present invention relates to a structure and a manufacturing method of a semiconductor optical integrated device using a multiple quantum well (MQW) structure.

[Conventional technology]

A semiconductor optical integrated device in which a light emitting region and a modulation region for modulating light emitted from the light emitting region are integrated on one semiconductor substrate is important as a small and high performance light source in high-speed optical fiber communication. . Among them, a semiconductor integrated device that integrates a distributed feedback semiconductor laser (hereinafter referred to as DFB laser) and an absorption type optical modulator is expected to play a central role as a light source for optical fiber communication of several Gb / s or more. ing. There are roughly the following three types of integrated elements of a conventional DFB laser and an optical modulator, each of which is characterized by an optical modulator. The first is the use of the Franz-Keldysh effect in the optical modulator, which passes by applying an electric field to the semiconductor layer with a slightly larger energy gap than the energy of the DFB laser formed in the optical modulator area. Modulates the laser light. This semiconductor optical integrated device is reported by, for example, Suzuki et al. (M. Suzuki e
tal., IEEE J. Lightwave Tech. LT-5, (1987) 1277).
Second, the optical modulator utilizes the quantum confined Stark effect, and modulates the DFB laser light transmitted by applying an electric field to the MQW layer formed in the optical modulator region. Kawamura et al. Reported on this semiconductor optical integrated device (Y.
Kawamura et al. IEEE J. Quantum Electron. QE-23, (19
87) 915). In the first and second conventional examples described above, the DFB laser region and the optical modulator region are composed of semiconductor layers having different compositions. Therefore, in manufacturing, first, on a semiconductor substrate
After the crystal growth of the DFB laser region, a method of selectively growing the optical modulator region is used. The third conventional example uses gain modulation in an optical modulator. The optical modulator region has an active layer having the same composition as the DFB laser region, and is injected into the active layer in the optical modulator region. The gain is changed by modulating the current to modulate the transmitted DFB laser light.
This semiconductor optical integrated device is reported, for example, by Yamaguchi et al. (M. Yamaguchi et al., Electron. Lett. 23, (198
7) 190). In the third conventional example, since the DFB laser region and the optical modulator region are composed of semiconductor layers having the same composition, the active layers in the two regions can be crystal-grown at the same time, and selective crystal growth is unnecessary. is there.

[Problems to be solved by the invention]

The conventional example described above has the following problems. First, in the first and second conventional examples, since it is necessary to use selective crystal growth when forming the optical modulator region, the production is difficult and the optical output from the optical modulator is small. There is. Liquid crystal epitaxial growth (LPE), vapor phase epitaxial growth (VPE), molecular beam epitaxial growth (MBE), etc. are used for selective crystal growth.
Either method tends to cause abnormal growth at the boundary between the DFB laser region and the optical modulator region. Further, since it is difficult to grow a uniform crystal of the semiconductor layer at the boundary, the optical coupling efficiency between the DFB laser region and the optical modulator region is as small as about 10% to 50%. As a result, the scattering loss of the laser light at the boundary increases, and the light output from the optical modulator decreases.
On the other hand, in the third conventional example, since selective crystal growth is not used, manufacture is relatively easy, and a coupling efficiency close to 100% can be realized. However, the modulation band is limited to 1 GHz or less because the optical modulator uses a gain change due to current injection.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the conventional example, to facilitate manufacture, realize an optical coupling efficiency close to 100%, and to perform modulation of several Gb / s or more. To provide a structure and a manufacturing method of a semiconductor optical integrated device in which the optical modulator and the optical modulator are integrated.

[Means for solving the problem]

The semiconductor optical integrated device of the present invention includes a semiconductor optical integrated device having at least a multiple quantum well layer on a semiconductor substrate, and a layer thickness of the multiple quantum well layer is different between a light emitting region and a light modulation region. A diffraction grating is provided between the substrate and the multiple quantum well layer, a multiple quantum well layer is collectively stacked on the light emitting region and the light modulation region, and the multiple quantum well layer of the light emitting region is a light modulation region. The energy gap is smaller than that of the multiple quantum well layer.

The method of manufacturing a semiconductor optical integrated device according to the present invention is directed to a method of manufacturing a semiconductor optical integrated device in which at least a multiple quantum well layer is formed on a semiconductor substrate and the thickness of the multiple quantum well layer is different between a light emitting region and a light modulation region. Forming a diffraction grating between the substrate and the multiple quantum well layer in the light emitting region, providing masks on both sides of the growth region of the diffraction grating, and growing the multiple quantum well layer in a portion other than the mask. It is characterized by.

The method of manufacturing a semiconductor optical integrated device according to the present invention is directed to a method of manufacturing a semiconductor optical integrated device in which at least a multiple quantum well layer is formed on a semiconductor substrate and the thickness of the multiple quantum well layer is different between a light emitting region and a light modulation region. And irradiating the growth region of the light emitting region with a laser beam to grow a multiple quantum well layer in the light emitting region and the light modulation region.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of a semiconductor optical integrated device of the present invention, and FIG. 2 is a sectional view taken along the line AA 'in FIG. In this embodiment, the DFB laser region 1 integrated on one semiconductor substrate is used.
00 and an optical modulator area 200. A structural feature is that the DFB laser region 100 includes an active layer composed of the first MQW layer 30, and the optical modulator region 200 includes a second MQW layer 40 having a larger energy gap than the first MQW layer. It is. The first MQW layer and the second MQW layer having different energy gaps are formed simultaneously by crystal growth.
However, the well layer of the first MQW layer has a slightly thicker layer thickness than the well layer of the second MQW layer, and has the same composition. Further, the barrier layers of the two MQW layers also have different layer thicknesses and have the same composition. When an electric field is applied to the second MQW layer, the laser light emitted from the DFB laser region 100 is modulated by the quantum confinement Stark effect. The first MQW layer 30, which is the active layer of the DFB laser region 100, is optically connected to the second MQW layer 40 of the optical modulator region 200. There is almost no optical scattering at the boundary between the region 100 and the light modulation region 200.
A coupling efficiency close to 00% can be realized. Therefore, the light output from the light modulator region 200 is large.

Hereinafter, the element structure will be described in detail while following the manufacturing procedure. First, an n-type InP in which the diffraction grating 80 is partially formed
Metalorganic vapor phase epitaxial growth (MOVP)
E) method, the n-type InGaAsP light guide layer 20, the first and second
The MQW layers 30, 40, the p-type InP clad layer 50, and the p-type InGaAsP cap layer 60 are sequentially grown. Here, the first and second MQW layers 30,
40 is composed of a both 10 periods of InGaAs well layers InGaAsP barrier layer (photoluminescence wavelength λ _{g =} 1.15μm). In this crystal growth, the first MQW layer 30 and the second MQW
The thickness of the layer 40 is changed to change the energy gap of each layer. This crystal growth method will be described later in detail when an example of a manufacturing method is described later. Next, an embedded structure for controlling the lateral mode is formed. First
After etching the central portions of the DFB laser region 100 and the optical modulator region 200 into a mesa shape, a high-resistance InP buried layer 90 doped with iron is grown on both sides of the mesa by MOVPE. Next, after attaching the electrode 70, an isolation groove 300 is formed between the two regions by etching. Finally, the element is cut out by cleavage, and an anti-reflection coating film 95 is formed on the end face of the optical modulator region 200. The lengths of the DFB laser region 100 and the optical modulator region 200 are 300 μm and 200 μm, respectively. The wavelength of the DFB laser light is about 1.55 μm, and the photoluminescence wavelength of the second MQW layer in the light modulation region 200 is about 1.48 μm. In this embodiment, since any structure does not require selective crystal growth as used in the conventional example, manufacture is easy, and
The optical coupling efficiency between the DFB laser region 100 and the optical modulator region 200 is close to 100%. For this reason, the optical modulator area 200 to 10 mW
The above light output is obtained. Further, since the quantum confined Stark effect is used as a modulation method, high-speed modulation of several Gb / s or more is possible.

An embodiment of the method of manufacturing a semiconductor optical integrated device according to the present invention will be described below with reference to FIG. FIG. 3 (a) is a plan view showing a surface of a semiconductor substrate before crystal growth of an MQW layer in a process of manufacturing an optical integrated device of a DFB laser and an optical modulator using the manufacturing method of the present invention. FIG. 3B is a sectional view taken along the BB 'axis after the crystal growth. The point of this embodiment is that the fact that the growth rate of each layer differs depending on the area of the growth region during crystal growth is utilized. As shown in FIG. 3 (a), the narrow diffraction grating region 4 sandwiched between the regions covered with the dielectric film 500 in the DFB laser region 100
The growth rate of the dielectric film 500 in the light modulator region 200
Faster than the growth rate of the region without. Therefore, FIG. 3 (a)
When a MQW layer is crystal-grown using MOVPE or the like on a semiconductor substrate partially covered with a dielectric film 500 as shown in
The thickness of the well layer of the first MQW layer grown in the laser region 100 (that is, the diffraction grating region 400) is larger than the thickness of the well layer of the second MQW layer grown in the optical modulator region 200. Therefore, the energy gap of the first MQW layer is smaller than the energy gap of the second MQW layer. The specific manufacturing procedure will be described below. First, a dielectric film 500 such as SiO ₂ is formed on the n-type InP substrate 10 on which the diffraction grating 80 is partially formed as shown in FIG. The width of the diffraction grating region 400 sandwiched between the regions covered with the dielectric film 500 is 10 μm.
Next, an n-type InGaAsP optical guide layer 20, first and second MQW layers 30, 40, a p-type InP cladding layer 50, and a p-type InGaAsP layer 60 are sequentially grown on this substrate by MOVPE (third type). Figure (b). Here, the first and second MQW layers 30, 40 are both 10
InGaAs well layers and InGaAsP barrier layers of the period (λ _{g =} 1.15μ
m). The thickness of the well layer of the first MQW layer 30 is about 8 nm
And the photoluminescence wavelength is 1.53 μm. Second
The thickness of the well layer of the MQW layer 40 is about 5 nm, and the photoluminescence wavelength is 1.48 μm. The subsequent manufacturing process is the same as the manufacturing method described in the embodiment shown in FIG. In this growth method, the light guide layer 20 other than the MQW layer is used.
Although the layer thickness such as that differs between the DFB laser region 100 and the optical modulator region 200, the difference in these layer thicknesses does not significantly affect the characteristics of the device.

There are several methods for simultaneously crystal-growing MQW layers having different well layer thicknesses on a semiconductor substrate in addition to the method using the patterned dielectric film 400 as described above. Even when used, the semiconductor optical integrated device of the present invention can be manufactured. For example, during crystal growth by MOVPE, D
There is also a manufacturing method that utilizes the fact that, when laser light is irradiated only to the FB laser region 200, the growth rate of the irradiated region increases and becomes larger than the layer thickness of the region not irradiated.

As described above, the structure and manufacturing method of the semiconductor optical integrated device of the present invention have been described in detail using the semiconductor optical integrated device of the DFB laser and the optical modulator as an example. It can be applied to optical integrated devices, such as an optical integrated device such as a tunable distributed Bragg reflection semiconductor laser and an optical modulator. In terms of crystal growth, MOVPE
Other than the method, for example, a hydride VPE method can be used. In terms of crystal material, the present invention can be applied to a semiconductor integrated device using another material system such as InGaAlAs.

〔The invention's effect〕

As described above, the present invention uses the MQW layer formed simultaneously by crystal growth in the light emitting region and the light modulation region, so that high optical coupling efficiency can be obtained easily and with high manufacturing efficiency.
This has the effect of realizing a semiconductor optical integrated device. In an embodiment in which a DFB laser and an optical modulator are integrated on a single semiconductor substrate, a semiconductor optical integrated device having a coupling efficiency close to 100% can be obtained without using a difficult manufacturing method such as selective crystal growth. Obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of the structure of a semiconductor optical integrated device of the present invention, FIG. 2 is a sectional view taken along line AA 'of FIG. 1, and FIG. It is a figure for explaining. In the figure, 100: DFB laser area, 200: Optical modulator area, 300: Separation groove, 400: Diffraction grating area, 500:
Dielectric film, 10 substrate, 20 light guide layer, 30 first
MQW layer, 40 ... second MQW layer, 50 ... clad layer, 60 ...
... cap layer, 70 ... electrode, 80 ... diffraction grating, 90 ... buried layer, 95 ... non-reflective coating film.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-321677 (JP, A) JP-A-1-319986 (JP, A) JP-A-61-107781 (JP, A)

Claims (3)

(57) [Claims] 1. A semiconductor optical integrated device having at least a multiple quantum well layer on a semiconductor substrate, wherein a thickness of the multiple quantum well layer is different between a light emitting region and a light modulation region. A diffraction grating is provided between the light emitting region and the light modulation region, and a multiple quantum well layer is collectively laminated on the light emitting region and the light modulation region. A semiconductor optical integrated device having a smaller energy gap than that of a semiconductor optical integrated device. 2. A method of manufacturing a semiconductor optical integrated device in which at least a multiple quantum well layer is formed on a semiconductor substrate and a thickness of the multiple quantum well layer is different between a light emitting region and a light modulation region. Forming a diffraction grating between the substrate and the multiple quantum well layer, providing masks on both sides of a growth region of the diffraction grating, and growing the multiple quantum well layer in a portion other than the mask. Device manufacturing method. 3. A method of manufacturing a semiconductor optical integrated device in which at least a multiple quantum well layer is formed on a semiconductor substrate and a thickness of the multiple quantum well layer is different between a light emitting region and a light modulation region. Forming a multiple quantum well layer in the light emitting region and the light modulation region while irradiating the semiconductor light with a laser beam.