JPH1084166A - Integrated optical semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a modulation signal from being leaked and to inhibit an increase in a wavelength chirp to make a long-distance optical transmission possible by a method wherein electrodes are provided on an optical waveguide path and a laser region and a modulation region are electrically separated from each other. SOLUTION: An integrated optical semiconductor device is constituted of an N-type InP substrate 1, a well active layer 2, a diffraction grating 3, a light absorption layer which is also used as an optical waveguide layer 4, a P-type InP clad layer 5, P-type contact layers 61 , 62 and 63 , P-type ohmic electrodes 71 , 72 , and 73 , an N-type ohmic electrode 8, insulating films 9, a high reflective film 10 and a non-reflective film 11. Moreover, the device is electrically separated into a laser region 12 and a modulation region 13 by an electrode separation region 14. When a reverse bias voltage is applied to the region 13, a leakage current from the region 13 is made to flow to the outside via the electrode 73 . Thereby, even if the voltage, which is applied to the region 13, is modulated, a modulation signal is prevented from being leaked in the region 12 and an increase in a wavelength chirp is inhibited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical semiconductor device, and more particularly to an optical semiconductor device in which a plurality of optical semiconductor elements are integrated.

[0002]

2. Description of the Related Art In recent years, research and development on long-distance and large-capacity trunk optical communication systems have been actively pursued. Semiconductor optical modulators that can achieve low chirp operation even during high-speed modulation,
It is a key device of a trunk optical communication system. In particular, the transmission light source can be realized at low cost by monolithically integrating the semiconductor optical modulator and the semiconductor laser.

FIG. 4 is a cross-sectional view of a conventional semiconductor optical modulator / semiconductor laser integrated light source taken along the waveguide direction. In the figure, 1 is an n-type InP substrate, 2 is a well active layer having an InGaAsP multiple quantum structure, 3 is a diffraction grating, 4 is InGa
An optical absorption layer and an optical waveguide layer having an AsP multiple quantum structure, 5 is a p-type InP cladding layer, 6 ₁ and 6 ₂ are p-type InGaAs.
A contact layer, 7 ₁ and 7 ₂ are p-type ohmic electrodes made of Au / Zu / Au, 8 is an n-type ohmic electrode made of AuGe / Ni / Au, 9 is an insulating film made of SiO ₂ ,
Reference numeral 10 denotes a high-reflection film made of a Si / SiO ₂ multilayer film, and 11 denotes a non-reflection film made of SiN _x .

[0004] In this optical semiconductor device, simultaneously with the laser oscillation by injecting a constant current into the active layer 2 through the p-type ohmic electrode _71, the light absorption voltage signal through the p-type ohmic electrode 7 ₂ Light intensity is modulated by applying to the layer 4. Here, the laser region 12 and the modulator region 1
3, an electrode separation region 14 is provided. In the electrode isolation region 14, the p-type InGaAs contact layer 6 is removed by etching so that the laser region 12 and the modulator region 13 are not electrically interfered.
However, the laser region 12 and the modulator region 13 need to be optically coupled via the optical waveguide layer 4, and the p-type InP cladding layer 5 needs to be provided on the optical waveguide layer 4 also in the electrode separation region 14. is there. Therefore, since the laser region 12 and the modulator region 13 are connected via the p-type InP cladding layer 5, they cannot be completely electrically separated from each other. Leakage current flows. As a result, when a voltage modulation signal is applied to the light absorption layer 4, the current injected into the active layer 2 is also modulated, which causes an increase in the wavelength chirp.

[0005]

As described above, in the conventional semiconductor optical modulator / semiconductor laser integrated light source, the laser region and the modulator region cannot be completely electrically separated from each other. There was a problem of causing an increase.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to completely increase the wavelength chirp by completely electrically separating a laser region and a modulator region. An object of the present invention is to realize a semiconductor optical modulator / semiconductor laser integrated light source without any problem.

[0007]

According to the present invention, in an optical semiconductor device in which a plurality of optical semiconductor elements are integrated so as to be connected via an optical waveguide, an electrode is provided on the optical waveguide. (Claim 1). As a preferred embodiment of the present invention, a constant voltage is applied to the electrode (claim 2), or the electrode is grounded (claim 3).

According to the present invention, an electrode is also provided on an optical waveguide connecting a plurality of optical semiconductor elements. Here, the electrode is formed to be in ohmic contact with the semiconductor material,
When a constant voltage is applied to the electrode, it is possible to keep the potential of the semiconductor layer below the electrode constant and to allow a leakage current to flow to the outside via the electrode. That is, the two optical semiconductor elements sandwiching the electrode can be completely electrically separated. As a result, even if one optical semiconductor element is electrically modulated, the modulation signal does not leak to the other optical semiconductor element. Further, when the electrode is grounded, it is possible to keep the semiconductor layer under the electrode at zero potential and at the same time to allow a leakage current to flow to the ground via the electrode. Therefore, also in this case, 2
The two optical semiconductor elements can be completely electrically separated.

Further, if the electrode is formed so as to make Schottky contact with a semiconductor material and a reverse bias voltage is applied to the electrode, the semiconductor layer below the electrode can be depleted. As a result, the two optical semiconductor elements sandwiching the electrode can be completely electrically separated.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a sectional view of a semiconductor optical modulator / semiconductor laser integrated light source according to a first embodiment of the present invention, which is perpendicular to the waveguide direction. In the figure, 1 is an n-type InP substrate, 2 is I
A well active layer composed of an nGaAsP multiple quantum structure, 3 is a diffraction grating, 4 is a light absorption layer and optical waveguide layer composed of an InGaAsP multiple quantum structure, 5 is a p-type InP cladding layer, 6 ₁ , 6
₂ , 6 ₃ are p-type InGaAs contact layers, 7 ₁ , 7
_2, 7 ₃ p-type ohmic electrode made of Au / Zu / Au, 8 are n-type ohmic electrode made of AuGe / Ni / Au, an insulating film made of SiO ₂ is 9, the 10 Si / Si
A high reflection film made of an O ₂ multilayer film, and 11 is a non-reflection film made of SiN _x . It should be noted that, usually, a T
A layer serving as a wiring from i / Pt / Au is provided, and a bonding pad is also formed of this material.

In this embodiment, an electrode separation region (for example, having a width of 5
0 μm) 14 in the p-type InGaAs contact layer 6 ₃ ,
It is provided with a p-type ohmic electrode 7 _3, the p-type ohmic electrode 7 ₃ constant forward bias voltage is applied.
Thus, p-type ohmic electrode 7 ₃ p-type InP cladding layer 5 below is maintained at a constant potential. At the same time, the modulator region (e.g. width of 20 through the p-type ohmic electrode 7 ₂
0 .mu.m) when a reverse bias voltage is applied to 13, the leakage current from the modulator region 13 flows to the outside through the p-type ohmic electrode 7 _3. As a result, even if the voltage signal applied to the modulator region 13 is modulated, the modulated signal does not leak to the laser region (for example, 400 μm in width) 12 and does not cause an increase in the wavelength chirp. Further, by setting the voltage applied to the p-type ohmic electrode 7 ₃ to the same value as the ON voltage of the active layer 2, p-type with the p-type ohmic electrode ₇₁ under the p-type ohmic electrode 7 ₃ below No potential difference occurs in the InP cladding layer 5. As a result, the laser region 12
There is no leakage current from the device, and there is no reduction in light output. Further, p-type ohmic electrode 7 _3, it is possible to p-type ohmic electrode 7 _1, 7 ₂ formed at the same time,
There is no need to increase the number of manufacturing steps.

(Embodiment 2) Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a cross-sectional view of a semiconductor optical modulator / semiconductor laser integrated light source according to a second embodiment of the present invention, which is perpendicular to the waveguide direction. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and description thereof will be omitted.

[0013] In this embodiment, p-type ohmic electrode 7 ₃ provided in the electrode isolation region 14 is grounded. Therefore, at the same time the p-type ohmic electrode 7 ₃ p-type InP cladding layer 5 below is maintained at zero potential, the laser region 12
A leakage current from the modulator region 13 flows to ground through the p-type ohmic electrode 7 _3. As a result, the laser region 1
2 and the modulator region 13 are completely electrically separated.
Further, p-type ohmic electrode 7 ₃ need only be connected to the earth, it is not necessary to increase the control terminal.

(Embodiment 3) Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 3 is a cross-sectional view of a semiconductor optical modulator / semiconductor laser integrated light source according to a third embodiment of the present invention, which is perpendicular to the waveguide direction. 3, the same components as those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and the description thereof is omitted.

In this embodiment, the Schottky electrode 1 is formed on the p-type InP cladding layer 5 in the electrode isolation region 14.
5 are formed. A reverse bias voltage is applied to the Schottky electrode 15, and the p-type InP cladding layer 5 below the Schottky electrode 15 is completely depleted. As a result, the laser region 12 and the modulator region 13 can be electrically separated. In addition, the Schottky electrode 15
The cross-sectional area of the lower p-type InP cladding layer 5 in the direction perpendicular to the waveguide direction is 20 μm ² , and the length of the Schottky electrode 15 made of, for example, Pt is 10 μm. Therefore, the capacitance of the depletion layer 16 is as small as about 0.2 fF, and the high frequency signal hardly leaks.

The present invention is not limited to the embodiment described above. In the embodiment, an InGaAsP-based semiconductor laser device has been described.
The present invention can be applied to various material systems such as an InGaAsSb system and a ZnCdSSe system. Further, in the embodiments, the device in which the semiconductor optical modulator and the semiconductor laser are integrated has been described. However, the present invention is also applicable to an element in which a plurality of optical modulators are integrated and an element structure in which an optical amplifier is integrated. The invention is valid. Further, a bulk material may be used for the active layer and the light absorbing layer, and the conductivity type of the semiconductor substrate is also n.
It is not limited to the mold substrate. In addition, various modifications can be made without departing from the spirit of the present invention.

[0017]

As described in detail above, according to the present invention,
The laser region and the modulator region can be completely electrically separated from each other, and no modulation signal leaks between the laser region and the modulator region. Therefore, it is possible to provide a semiconductor light modulator / semiconductor laser integrated light source capable of long-distance optical transmission without increasing the wavelength chirp. As a result, a transmission light source of the trunk optical communication system can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a semiconductor optical modulator / semiconductor laser integrated light source according to a first embodiment of the present invention, taken along a waveguide direction.

FIG. 2 is a cross-sectional view of a semiconductor optical modulator / semiconductor laser integrated light source according to a second embodiment of the present invention, taken along a waveguide direction.

FIG. 3 is a cross-sectional view of a semiconductor optical modulator / semiconductor laser integrated light source according to a third embodiment of the present invention, taken along a waveguide direction.

FIG. 4 is a cross-sectional view of a conventional semiconductor optical modulator / semiconductor laser integrated light source along a waveguide direction.

[Explanation of symbols]

1 ... n-type InP substrate 2 ... active layer 3 ... diffraction grating 4 ... light absorbing layer and light waveguide layer 5 ... p-type InP cladding layer 6 _1, 6 _2, 6 ₃ ... p-type InGaAs contact layer 7 _1, 7 _2, 7 ₃ ... p-type ohmic electrode 8 ... n-type ohmic electrode 9 ... insulating film 10 ... high-reflection film 11 ... non-reflection film 12 ... laser region 13 ... modulator region 14 ... electrode separation region 15 ... p-type Schottky electrode 16 ... Depletion layer

Claims (4)

[Claims] 1. An integrated optical semiconductor device comprising a plurality of optical semiconductor elements connected via an optical waveguide, wherein an electrode is provided on a part of the optical waveguide. 2. The integrated optical semiconductor device according to claim 1, wherein a constant voltage is applied to said electrode. 3. The integrated optical semiconductor device according to claim 1, wherein said electrode is grounded. 4. An integrated optical semiconductor device comprising: a semiconductor laser provided on one substrate; an optical waveguide for guiding light from the laser; and an optical modulator for modulating light from the optical waveguide. An integrated semiconductor device, wherein an electrode is provided on a part of the optical waveguide via an insulating layer.