JPH0521832A - Semiconductor light receiving element - Google Patents

Abstract

PURPOSE:To reduce the leakage current of a light receiving element formed in an optoelectronic integrated circuit and make the construction of the element most advantageous to the manufacture. CONSTITUTION:One of a pair of metal electrodes to be formed on a GaAs substrate 1 is a Schottky electrode 4; the other is an ohmic electrode 3 formed on a p-type layer 2, an impurity diffusion region. Since the p-type layer 2 is formed on the ohmic electrode 3 side, the electron current, the major component of the leakage current, is controlled by diffusion, not the thermal radiation from the Schottky barrier, being reduced. Since the p-type layer 2 is formed only on the ohmic electrode 3 side, the number of processes is not increased and remarkable increase in the area of occupation is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to MSM (metal-semiconductor-
The present invention relates to a semiconductor light receiving element having a (metal) structure, and particularly to a semiconductor light receiving element that can function as a light receiving element in an optoelectronic integrated circuit (OEIC).

[0002]

2. Description of the Related Art At present, in an optical data transmission system, an optical device for emitting and receiving light and an electronic device for driving the same are hybridized. These electronic devices and optical devices are integrated into one chip. By using an optoelectronic integrated circuit (OEIC) formed in the inside, stray capacitance and inductance can be reduced, and high-speed operation is possible. Therefore, research and development thereof are active (for example,
“Monolithic Integrationof Metal-Semiconductor-Met
al Photodiode and a GaAs Preamplifier ”, IEEE
E, Electron Device Letter Vol.EDL-5, pp.531-532,19
See 1984. ).

For example, an electronic device for amplification is MES-
In the case of a FET (Metal Shottky FET), it is convenient in the manufacturing process to uniformly use each electrode on the chip as a Schottky electrode. Therefore, when the MSM structure is adopted as the light receiving element, both the positive electrode and the negative electrode are usually Schottky electrodes in many cases.

[0004]

However, when both metal electrodes of the light receiving element are made of Schottky electrodes, there is a drawback that leakage current to the light receiving region becomes large.

That is, when the light receiving element is in the light receiving state, electron-hole pairs are generated in the light receiving region of the semiconductor region in response to incident light. There are holes and holes, and the inflowing electrons and holes are used as a leakage current. When this leakage current is large, the sensitivity of the light receiving element becomes low, and as a result, the response characteristics deteriorate.

The leakage current is divided into an electron current component and a hole current component. The electron current component In is K * Mn * ex.
It can be represented by p (VBn), and the hole current component Ip is
It can be represented by K * Mp * exp (VBp) (where Mn is the effective mass of electrons, Mp is the effective mass of holes, V
Bn is the Schottky barrier height for electrons, VBp is the Schottky barrier height for holes, and K is a proportional constant. ). Among them, since the electron current component In is not particularly small, the whole leakage current becomes large.

In order to improve the leakage current characteristic, it is possible to bring both metal electrodes of the light receiving element into ohmic contact. However, in order to bring the metal electrode into ohmic contact, it is necessary to form the electrode in a step different from that of the MES-FET on the same chip. Further, in order to form the ohmic electrode, the area sufficient for impurity diffusion is sufficient. Since it is necessary to lay out the electrodes at intervals, the area occupied by the electrodes on the chip increases.

In view of the above-mentioned technical problems, the present invention has an object to provide a semiconductor light receiving element capable of reducing the leakage current to the light receiving region.

[0009]

In order to solve the above-mentioned technical problems, a semiconductor light receiving element of the present invention has a semiconductor region serving as a light receiving region between a pair of metal electrodes, and one of the metal electrodes is provided. An impurity diffusion region for ohmic contact is formed.

If the electron current is the main component of the leakage current, the p-type layer may be formed as the impurity diffusion region on the negative electrode side, and if the hole current is the main component,
An n-type layer is formed on the positive electrode side as an impurity diffusion region. The metal electrode may have, for example, a comb-shaped electrode structure. In the present invention, since the impurity diffusion region is formed, a pair of metal electrodes having different contact characteristics can be formed of the same metal material.

[0011]

By using one of the metal electrodes as an ohmic electrode in ohmic contact, it is possible to reduce leakage of carriers, which is dominant in leakage current, into the light receiving region.

For example, when the electron current component is the main component of the leakage current, I in the case of the conventional Schottky barrier.
Since the electron current given by n = K * Mn * exp (VBn) forms an impurity diffusion region for ohmic contact, the electron current In is A * q * (Dn /
L) * (ni / Nd) (note that D
n is the diffusion length of electrons, L is the distance between electrodes, ni is the intrinsic carrier concentration of the semiconductor of the substrate, Nd is the acceptor impurity concentration of the p region, q is the elementary charge, and A is the negative electrode area. ). This change is dominated by the diffusion from the impurity diffusion region in the light receiving element of the present invention, whereas the electron current component is dominated by the thermal radiation from the Schottky barrier in the conventional structure in which the impurity diffusion region is not formed. Will be done. By making the electron current component due to such diffusion control, the electron current component can be reduced and the leakage current can be suppressed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the drawings.

This embodiment is a semiconductor light receiving element in a light receiving optoelectronic integrated circuit, and is an element suitable for use in an optical data transmission system that requires high-speed operation. FIG. 1 shows a cross-sectional view of the device of this example.

As shown in FIG. 1, in the light receiving element of this embodiment, both the ohmic electrode 3 and the Schottky electrode 4 are formed on the surface of the semi-insulating GaAs substrate 1, and the ohmic electrode 3 is formed. A p-type layer 2 composed of a p-type impurity diffusion region is formed on the substrate surface.

The GaAs substrate 1 is a substrate for forming an optoelectronic integrated circuit, and although not shown, an MES-FET as a transistor for amplification is also formed on the same substrate. In the present embodiment, the GaAs substrate 1 is semi-insulating, but is not limited to this, and may be a sufficiently low concentration n-type or p-type compound semiconductor substrate.

The p-type layer 2 is a high-concentration impurity diffusion region formed on the surface of the GaAs substrate 1 where the ohmic electrode 3 is formed. This p-type layer 2
Can be formed, for example, by selectively doping the surface of the GaAs substrate 1 with zinc. By forming such a p-type layer 2, ohmic contact can be obtained with respect to the formed electrode as described later.

The ohmic electrode 3 is a metal electrode that functions as a negative electrode of the light receiving element, and is formed on the p-type layer 2 in a required comb-shaped pattern, for example. In this embodiment, each material is Ti / Pt / Au.

The Schottky electrode 4 is a metal electrode which functions as a positive electrode of the light receiving element and is formed on the surface of the GaAs substrate 1. The Schottky electrode 4 is also patterned to have a comb structure, for example, and faces the ohmic electrode 3. The Schottky electrode 4 is made of the same Ti / Pt / Au material as the ohmic electrode 3, and is formed in the same step as the ohmic electrode 3. In addition, the Schottky electrode 4 formed directly on this substrate
Is also formed as the gate electrode of the MES-FET.

The light receiving element of this embodiment having this structure is biased so that the Schottky electrode 4 becomes the positive electrode and the ohmic electrode 3 becomes the negative electrode, and when light is incident from above the light receiving element, the GaAs substrate 1 Electron-hole pairs are generated inside the. The generated electrons are attracted to the Schottky electrode 4, and the generated holes are attracted to the ohmic electrode 3, and a photocurrent is generated.

FIG. 2 is a band diagram of a current path between the ohmic electrode 3 and the Schottky electrode 4. The potential difference between the negative ohmic electrode 3 and the positive Schottky electrode 4 is the bias voltage. The Schottky electrode 4 is connected to the GaAs substrate 1 with a Schottky barrier. The ohmic electrode 3 is brought into ohmic contact due to the p-type layer 2 formed on the surface of the GaAs substrate 1, and the permissible band of the ohmic electrode 3 and the valence band of the p-type layer 2 have almost the same energy. Contact at the level. In the region of the p-type layer 2, the band is almost at the same level, and in the region of the GaAs substrate 1, the conduction band and the valence band are inclined according to the bias voltage.

Focusing on currents other than the photovoltaic current at the time of bias, in the region of the GaAs substrate 1, the hole current from the Schottky electrode 4 and the electron current injected from the p-type layer 2 become leakage currents. .. Regarding carriers from the ohmic electrode 3, electrons become minority carriers in the p-type layer 2,
Moreover, as shown in FIG. 2, since the ohmic electrode 3 is in contact with the barrier having a high conduction band, the occurrence of the tunnel phenomenon is suppressed and the leakage current does not become a problem. Then, as described above, the electrons from the p-type layer 2 are dominated by diffusion, and thus are reduced as compared with those dominated by thermal radiation from the conventional Schottky barrier. Schottky electrode 4
The hole current from the above is negligible compared to the electron current, and the formation of the p-type layer 2 significantly reduces the leak current.

In the light receiving element of this embodiment, the p-type layer 2
Is formed only on the negative electrode side of the ohmic electrode 3, and the occupied area increases due to the impurity diffusion only on the ohmic electrode 3 side. Furthermore, even if one of the electrodes is an ohmic electrode and the other is a Schottky electrode, all of them can be formed of the same material layer, including the gate electrode of the MES-FET that is simultaneously formed. Therefore, the number of steps does not increase in the process.

In the above embodiments, the electron current is the main component of the leakage current, but when the hole current is the main component of the leakage current, the high-concentration impurity diffusion is performed only on the positive electrode side. It is also possible to form an n-type layer in the region to have a structure in which a hole current is suppressed. The n-type layer may be formed by doping the surface of the substrate on which the positive electrode is provided with silicon or the like. Further, although the GaAs substrate is used in the present embodiment, it goes without saying that the present invention may be an element formed on another semiconductor substrate such as InP.

[0025]

In the semiconductor light receiving element of the present invention, the impurity diffusion region for making ohmic contact with one of the metal electrodes is formed, and the impurity diffusion region suppresses the leakage current. Therefore, a highly sensitive light receiving element can be obtained. In particular, when the semiconductor light receiving element of the present invention is used in an optoelectronic integrated circuit, electrodes and the like can be formed in the same process as that for driving and amplifying transistors on the same substrate.
Manufacturing is possible without a significant increase in the number of steps. Further, in the present invention, since the impurity diffusion region is formed only on one side of the metal electrode, the occupied area does not need to be increased.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an example of a semiconductor light receiving element of the present invention.

FIG. 2 is an energy band diagram along a current path in an example of the semiconductor light receiving element of the present invention.

[Explanation of symbols]

 1 ... GaAs substrate 2 ... p-type layer 3 ... ohmic electrode 4 ... Schottky electrode

Claims (1)

Claim: What is claimed is: 1. A semiconductor light receiving device having a semiconductor region serving as a light receiving region between a pair of metal electrodes, wherein an impurity diffusion region for making ohmic contact with one of the metal electrodes is formed. Semiconductor light receiving element.