JPS6220382A - Optical semiconductor device - Google Patents

Abstract

PURPOSE:To increase sensitivity, by laminating a very thin metal layer, which forms a Schottky barrier and has a thickness so that light can be transmitted, on a semiconductor active layer, thereafter laminating a transparent electrode layer on the metal layer, and forming low resistance electrodes. CONSTITUTION:On a semi-insulating GaAs substrate 1, a non-doped GaAs active layer 2 is laminated. Electrodes 4 and 5 are formed thereon. Each electrode is formed by two layers. At first, a WSiX layer 8 is laminated as a Schottky barrier metal layer. Then a transparent electrode layer 9 is laminated on the WSiX layer 8. As a material for the transparent layer, ITO or SnO2 is used. The width and the interval of the electrode layers are patterned in about 3mum. The pattern, in which the electrodes 4 and 5 are alternately connected, is formed. The light transmittance in the electrode part is about 80%. Thus, the element characterized by less dark current and high sensitivity is formed.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to an optical semiconductor device using a compound semiconductor and suitable for monolithic integration with a transistor, and an MSM photodiode known as 1-7. ing.

WSix as electrode +4 material of MSM photodiode
It has already been proposed to reduce the dark current by using a transparent electrode material, but we also improved the photosensitivity by using a transparent electrode material.

[Industrial application field]

The present invention is based on MSM (Metal Semiconductor).
The present invention relates to improving the photosensitivity of an optical semiconductor device having a photodiode (Metal) photodiode.

MSM FoI diodes, which have a metal electrode that can form a Schottky barrier with materials such as compound semiconductors, especially GaAs and InP, are attracting attention for their future potential due to their wavelength sensitivity or response speed.

Furthermore, in optical semiconductor devices using GaAs semiconductors, it is possible to easily monolithically form GaAs FETs on the same four substrates, and a wide range of applications as optical integrated circuits are expected. There are still issues that need to be addressed and improvements are requested.

[Conventional technology]

The structure of a conventional MSM7Ai diode will be explained with reference to the drawings.

FIG. 2 shows a plan view of the main part of the GaAs MSM photo diode 1', and FIG. 3 shows a sectional view of the main part taken along the line X--X in FIG.

In the figure, 1 is a semi-insulating GaAs substrate, 2 is a non-doped GaAs active layer, and 4 and 5 are comb-shaped electrodes, respectively.

Light enters the gap between the comb-shaped electrodes 4.5, and in order to increase the light receiving sensitivity, a Si3N4 film 3 is laminated as a non-reflective coating film in this region.

Although only the photodiode element is shown in FIGS. 2 and 3, there is also an n-type GaA layer in another area on the same substrate.
MESFET (Metal S
emiconductor F 1eld E f
fectTransistor).

As the material of the electrode 4.5 described above, A7! is commonly used in semiconductor devices! When using the MSM photodiode (2), the problem arises that the dark current increases and the S/N ratio decreases.

The reason for this will be briefly explained using the energy hand diagram of the MSM photodiode shown in FIG.

In the drawing, M represents a metal electrode portion, S represents a semiconductor layer, and a state in which a negative bias voltage of V port is applied to the electrode on the left side of the drawing is shown.

6 and 7 indicate the energy levels of the conduction band and valence band of the semiconductor layer, respectively, and ψ and 9 indicate the barrier to the conduction band.
High (·, φ, p are the barrier/hyde to the valence band.

The injected electron component j and the injected hole component jl as dark current are current components that flow over the barrier hides φ, w, ψ, and p, respectively, and to minimize the dark current, Je+Jh It is sufficient to satisfy the following conditions to make the barrier/hide uniform for each.

φ1. ．． ″q’ABg=　lφ, 2( Here, Eg represents the energy gap of the semiconductor layer.

The present inventor has already proposed that WSj is suitable as a metal material that satisfies the above conditions. (Application filed May 25, 1986) [Problem to be solved by the invention] The above-mentioned WS
The method using ix has a problem in that the area of the semiconductor layer cannot be used effectively because the light transmittance at the electrode surface is low. In other words, only the light that can enter the gaps between the comb-shaped electrodes is used.

In order to improve the light transmittance by reducing the thickness of the electrode of WSi, since the resistivity of WSix is high, the electrode resistance becomes large, and the thickness cannot be made sufficiently small.

WSi as a metal layer that can form a Schottky barrier,
An improvement would be to increase the sensitivity of the MSM photodiode by using electrodes, without increasing the electrode resistance, and by increasing the light transmittance.

[Means for solving problems]

The above problem is solved by the structure of the present invention, in which WSi has only the function of a Schottky barrier to reduce dark current, and the function as an electrode conductor is replaced by another transparent electrode material. Ru.

That is, after laminating an extremely thin metal layer that forms a Schottky barrier on a semiconductor active layer to a thickness that allows light to pass through, a transparent electrode layer is laminated on the metal layer to form a low-resistance electrode. By doing so, you can increase your sensitivity.

[Effect]

The WSix layer is laminated thin enough as a metal layer, but there is no problem with its function as a Schottky barrier.
In addition, most of the light is transmitted to the semiconductor layer.

In order to reduce the resistance of the electrode material, the problem can be eliminated by forming a laminated layer with good light transmittance on the WSiX layer-1.

In other words, a thin metal layer for a Schottky barrier and a thick light-transmitting conductive layer are laminated.

〔Example〕

An embodiment according to the present invention will be described in detail with reference to the drawings. The basic structure of a semiconductor device is explained in Figs. 2 and 3.
() has not changed for a long time.

Since the feature of the present invention lies in the structure 6 of the electrode portion, this portion will be explained with reference to FIG. 1, which is an enlarged view of this portion. semi-insulating caAs
, 1 & 1, a non-1-p Ga As layer 2 is laminated, and electrodes 4 and 5 are formed thereon.

'The electrode is composed of two layers:
-f layer and J, 7 (7') W S i , layer 8
laminate one layer to a thickness of 1.00 to 200 people. When the mixed crystal ratio X of Si is 0.64 and 6.7j, the best result is 2+f+, which is the same as the method already proposed.

Next, a transparent electrode layer 940.5 to 1 of WSiX8 is formed.
．． 0, +, rm stack. The material of the transparent electrode layer and 7 are G, 1, I TO (Indium "I" in 0xi
de) or S n O2 is used.

These electrode layers are patterned to have widths and intervals of about 3 μm, respectively, and form a pattern in which electrodes 4 and 5 are interconnected by -C.

With the structure described below, the light transmittance of the electrode portion can be secured at a value of t, 780%. Therefore, almost the entire area of the light receiving surface contributes to generation of effective current 74-.

1-7 is omitted in Fig. 1, but by coating the Si3N4 film 3 of C as a non-reflective coating film, as explained in Fig. 3, it is possible to expect an improvement in sensitivity. I didn't argue.

〔Effect of the invention〕

As described in [-18], the structure of the optical semiconductor device of the present invention is applied, and as per G, MSM photo die: 4
-1, an element with low dark current and high sensitivity is formed.In history, it is possible to integrate MIi and SFET on the same substrate and form GJ'. It is more suitable for use as an optical integrated circuit.

Furthermore, the present application does not limit the material to the WS i layer.

[Brief explanation of the drawing]

FIG. 1 is a sectional view illustrating the structure of the electrode part of the optical conductor device according to the present invention, FIG. 2 is a plan view of the main part of the MSM phytodiode 1, and FIG. Figure 4 is an energy Hunt diagram for explaining the characteristics of MsM-,7:t-dio-1. In the drawings, 1 is a semi-insulating GaAs substrate, 2 is a non-doped GaAs active layer, and 3 is a 5iaN4
4.5 is an electrode, 6 is a conduction band, 7 is a valence band, 8 is a metal layer (WSiX layer), and 9 is a transparent electrode layer.

Claims (1)

[Claims] In an MSM photodiode, a semiconductor active layer (2
), a metal layer (8) having the semiconductor active layer and a Schottky barrier formed thereon is laminated to a thickness that allows light to pass through, and then a transparent electrode layer (9) is laminated on the metal layer. Features of optical semiconductor devices.