JPH06302847A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To enhance the optoelectronic conversion efficiency of a semiconductor photodetector utilizing a field-effect transistor by a method wherein the field- effect transistor is formed on an optical waveguide formed on a semiconductor substrate and an active layer for the field-effect transistor is coupled optically to the optical waveguide. CONSTITUTION:An optical waveguide 2 is formed on a semiconductor substrate 1, a field-effect transistor is formed on the optical waveguide 2, and an active layer 3 for the field-effect transistor is coupled optically to the optical waveguide 2. For example, an optical waveguide 2 composed of InGaAsP is formed on the surface of 3 semiinsulating semiconductor substrate 1 composer of InP. In addition, 3 semiconductor layer 2 of a two-layer structure by an InGaAs layer for forming an active layer 3 for a field-effect transistor and by an InAlAs layer forming a Schottky-junction assist layer 4 is formed in such a way that the back side comes into contact with the optical waveguide layer 2. In addition, a Schottky electrode 6 and ohmic electrodes 7, 8 are formed on the surface of the semiconductor layer 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light receiving element,
In particular, the present invention relates to improving the efficiency of photoelectric conversion of a field effect transistor capable of receiving an optical signal.

[0002]

2. Description of the Related Art FIG. 5 shows a conventionally proposed field effect transistor for light reception. In FIG. 5, the field-effect transistor includes an n-type semiconductor layer 10 on a semi-insulating substrate 101 made of, for example, GaAs or InP.
2 is formed in a plateau, and a Schottky electrode 103 is formed on the semiconductor layer 102 so as to separate the surface of the region including the semiconductor layer 102 into two regions. A source electrode 104 and a drain electrode 105 are formed on each of the two regions.

In the field effect transistor having such a structure, if an optical signal is applied to the active layer immediately below the Schottky electrode 103 while the load is connected via the bias power supply, the optical signal is generated by a known principle. An optical signal receiving function is obtained in which an amplified output controlled according to the signal is generated in the load.

[0004]

However, when the above-mentioned conventional field effect transistor is used as a light receiving element,
Due to the following reasons, it has been difficult to realize a sufficient photoelectric conversion function regardless of which direction an optical signal is incident. This has been a factor that impedes the efficiency of photoelectron conversion. (1) When an optical signal is incident from the surface of the semi-insulating substrate 101: Since an optical signal is incident on the active layer through the space between the electrodes 103, 104 and 105, these electrodes 103, 104 and 105 are used. The optical signal is blocked, and the photoelectric conversion effect is blocked accordingly. (2) When an optical signal is incident from the back surface of the semi-insulating substrate 101: (a) When the semi-insulating substrate 101 is a GaAs substrate,
Since the optical signal is absorbed by the GaAs substrate, the optical signal cannot be efficiently incident on the active layer. (B) In the case where the semi-insulating substrate 101 is an InP substrate, since there is a distance corresponding to the thickness of the substrate 101 between the light source and the active layer, an optical signal is diffused, so that the light source efficiently transmits light to the active layer. It is difficult to collect signals and make them incident.

Therefore, the present invention aims to improve the photoelectron conversion efficiency of a semiconductor light receiving element using a field effect transistor.

[0006]

In the semiconductor light receiving element of the present invention which achieves the above object, an optical waveguide is formed on a semiconductor substrate, a field effect transistor is formed on the optical waveguide, and an active layer of the field effect transistor is formed. And the optical waveguide are optically coupled. That is, the semiconductor light receiving element of the present invention is greatly different from the prior art in that the field effect transistor is formed with the optical waveguide optically coupled to the active layer.

[0007]

In the semiconductor light receiving element of the present invention, the optical signal is incident on the optical waveguide and is coupled from the optical waveguide to the active layer. Therefore, it is possible to avoid the factor that hinders the incidence of the optical signal on the active layer as in the related art, and it is possible to improve the efficiency of the photoelectric conversion from the optical signal to the electric signal as compared with the related art.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIG. 1 shows a sectional structure of a semiconductor light receiving element according to a first embodiment of the present invention, and FIG. 2 shows its manufacturing process. In the semiconductor light receiving element shown in FIG. 1, an optical waveguide 2 made of InGaAsP is formed on the surface of a semi-insulating semiconductor substrate 1 made of InP. Further, from the semiconductor substrate 1 side, a semiconductor layer 5 having a two-layer structure in the order of an InGaAs layer forming the active layer 3 of the field effect transistor and an InAlAs layer forming the Schottky junction assist layer 4 is formed on the optical waveguide 2. It is formed in a plateau shape so that the back surfaces are in contact with each other. Further, a Schottky electrode 6 is formed on the surface of the semiconductor layer 5 so as to divide the surface region of the semiconductor layer 5 into two, and further, the Schottky electrode 6 divides the surface of the semiconductor layer 5 into two parts. Ohmic electrodes 7 and 8 are connected to each of the two regions. With this structure, the InGaAs layer is used as the active layer 3 and each electrode 6,
A field effect transistor having gate electrodes 7, source electrodes, and drain electrodes 7 and 8 is formed.

The manufacturing method of this field effect transistor is as follows.
A description will be given based on FIG. (1) As shown in FIG. 2A, an InGaAsP semiconductor layer 2 ′ serving as an optical waveguide is formed on a semi-insulating semiconductor substrate 1 made of InP by a known method, MOVPE.
Grow by law. (2) Next, as shown in FIG. 2 (B), a well-known wet etching process is applied to the InGaAsP other than the portion to be the optical waveguide by using a mask.
The semiconductor layer 2'is removed to form the optical waveguide 2. (3) Next, as shown in FIG. 2C, first, InGaA
In the region where the sP semiconductor layer is removed, the semi-insulating InP layer 9 is selectively grown by the MOVPE method, and the optical waveguide 2 is buried in the semi-insulating InP layer 9 leaving the surface thereof. (4) Thereafter, as shown in FIG. 2D, the InGaAs layer 3'and the InAlAs layer 4'are grown in this order by MOVPE. (5) Next, as shown in FIG. 2E, the InG of the terraced field effect transistor is formed by a method known per se for the InGaAs layer 3'and the InAlAs layer 4 '.
A semiconductor layer 5 including an aAs active layer 3 and a Schottky junction assist layer 4 is formed. In this case, the InGaAs active layer 3 and the Schottky junction assist layer 4 are formed so as to be divided into two regions by the optical waveguide 2. (6) Next, as shown in FIG. 1, the Schottky electrode 6
The surface of the Schottky junction assist layer 4 is divided into two regions, and the Schottky junction assist layer 4 and InG are formed.
It is formed so as to face or cross the optical waveguide 2 via the aAs active layer 3. Finally, ohmic electrodes 7 and 8 are formed in two regions on the surface of the Schottky junction assist layer 4 divided by the Schottky electrode 6 by a method known per se. As a result, the semiconductor light receiving element shown in FIG. 1 is obtained.

According to the above-described semiconductor light receiving element, when an optical signal is incident on the optical waveguide 2 with a load connected between the source / drain electrodes 7 and 8 via a bias power supply, the InGaAs active layer 3 of the field effect transistor 3 InGaA having a higher refractive index than the optical waveguide 2 on the lower surface
s Light is coupled to the active layer 3 and InGa under the gate electrode 6 is formed.
Electron hole pairs are generated in the As active layer 3. As a result, the electric field in the InGaAs active layer 3 immediately below the gate electrode 6 is changed, the drain current is modulated, and an amplification output corresponding to the light intensity is generated in the load, which is an amplification function.

Incidentally, the structure of the active layer and the gate electrode of the field effect transistor is a junction gate type field effect transistor (junction field effect transistor), and a high electron mobility field effect transistor (High Electro Electron Mobility Field Effect Transistor).
It is clear that the same function as described above can be obtained in any case of n Mobility Transistor).

Even if the refractive index of the optical waveguide 2 and the refractive index of the active layer 3 are the same or the refractive index of the active layer 3 is low, the light guided through the optical waveguide 2 is It is clear that a light-receiving operation is possible, since the part is always coupled to the active layer 3.

<Second Embodiment> Next, a second embodiment of the present invention will be described. FIG. 3 shows a sectional structure of the semiconductor light receiving element, and FIG. 4 shows its manufacturing process. In the semiconductor light receiving element shown in FIG. 3, I is provided inside the semi-insulating semiconductor substrate 1 made of InP.
An optical waveguide 2 made of nGaAsP is embedded.
Further, the semiconductor substrate 1 is sandwiched on the optical waveguide 2 from the semiconductor substrate 1 side, for example, an InGaAs layer and a Schottky junction assist layer 4 forming the active layer 3 of the field effect transistor.
The semiconductor layer 5 having a two-layer structure is formed in a plateau shape with the back surface facing the optical waveguide 2 in the order of, for example, the InAlAs layer. Further, a Schottky electrode 6 is formed on the surface of the semiconductor layer 5 so as to divide the surface region of the semiconductor layer 5 into two.
The ohmic electrodes 7 and 8 are connected to the two divided regions of the surface of the semiconductor layer 5, respectively. With this structure, the InGaAs layer is used as the active layer 3 and each electrode 6, 7,
A field effect transistor having a gate electrode, a source electrode, and a drain electrode 8 is formed.

A method of manufacturing this field effect transistor will be described below.
It will be described with reference to FIG. (1) As shown in FIG. 4A, an InGaAsP semiconductor layer 2 ′ serving as an optical waveguide is formed on a semi-insulating semiconductor substrate 1 made of InP by a known method, MOVPE.
Grow by law. (2) Next, as shown in FIG. 4B, the InGaAsP other than the portion to be the optical waveguide is subjected to a known wet etching process using a mask.
The semiconductor layer 2'is removed to form the optical waveguide 2. (3) Next, as shown in FIG. 4C, first, InGaA
In the region where the sP semiconductor layer is removed, the semi-insulating InP layer 9 is selectively grown by the MOVPE method, and the optical waveguide 2 is completely embedded in the semi-insulating InP layer 9. (4) After that, as shown in FIG. 4D, the InGaAs layer 3'and the InAlAs layer 4'are grown in this order by MOVPE. (5) Next, as shown in FIG. 4 (E), the InG of the terrace-shaped field effect transistor is formed by a method known per se for the InGaAs layer 3'and the InAlAs layer 4 '.
A semiconductor layer 5 including an aAs active layer 3 and a Schottky junction assist layer 4 is formed. In this case, the InGaAs active layer 3 and the Schottky junction assist layer 4 are formed so as to be divided into two regions by the optical waveguide 2. (6) Next, as shown in FIG. 3, the Schottky electrode 6
The surface of the Schottky junction assist layer 4 is divided into two regions, and the Schottky junction assist layer 4 and InG
It is formed so as to face or cross the optical waveguide 2 via the aAs active layer 3. Finally, ohmic electrodes 7 and 8 are formed in two regions on the surface of the Schottky junction assist layer 4 divided by the Schottky electrode 6 by a method known per se. As a result, the semiconductor light receiving element shown in FIG. 3 is obtained.

According to the above-mentioned semiconductor light receiving element, when an optical signal is incident on the optical waveguide 2 with a load connected between the source / drain electrodes 7 and 8 via a bias power source, the InGaAs active layer 3 of the field effect transistor 3 On the lower surface, the light exuding from the optical waveguide 2 is coupled to the InGaAs active layer 3 via the InP layer 9, and I under the gate electrode 6
Electron hole pairs are generated in the nGaAs active layer 3. As a result, the electric field in the InGaAs active layer 3 immediately below the gate electrode 6 is changed, the drain current is modulated, and an amplification output corresponding to the light intensity is generated in the load, which is an amplification function.

In the case of the present embodiment as well, the structure of the active layer and the gate electrode of the field effect transistor is either a junction gate type field effect transistor or a high electron mobility field effect transistor. Obviously, the same function as described above can be obtained.

Further, even if the refractive index of the optical waveguide 2 and the refractive index of the active layer 3 are the same or the refractive index of the active layer 3 is low, one It is clear that a light-receiving operation is possible, since the part is always coupled to the active layer 3.

[0019]

According to the semiconductor light receiving element of the present invention, an optical signal can be made incident on the active layer of a field effect transistor through an optical waveguide optically coupled thereto.
The active layer can be irradiated with light without being affected by the electrodes or the semiconductor substrate. Therefore, the efficiency of photoelectron conversion can be improved as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor light receiving element according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a manufacturing process of the semiconductor light receiving element of FIG.

FIG. 3 is a sectional view of a semiconductor light receiving element according to a second embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a manufacturing process of the semiconductor light receiving element of FIG.

FIG. 5 is a sectional view of a conventional semiconductor light receiving element.

[Explanation of symbols]

1 Semi-insulating semiconductor substrate 2 Optical waveguide 3 InGaAs active layer of field effect transistor 4 Schottky junction assist layer of field effect transistor 5 Semiconductor layer 6 Schottky electrode (gate electrode) 7 Ohmic electrode (source electrode) 8 Ohmic electrode (drain) Electrode) 9 InP layer

Claims (1)

[Claims] 1. An optical waveguide is formed on a semiconductor substrate, a field effect transistor is formed on the optical waveguide, and an active layer of the field effect transistor and the optical waveguide are optically coupled. Semiconductor light receiving element.