JPS6286877A - Photodetector - Google Patents

Abstract

PURPOSE:To improve the rise of a response by reducing the thickness of a light absorbing layer of a portion formed with a pair of ohmic electrodes formed on the light absorbing layer thinner than that of the other portion. CONSTITUTION:An InGaAs light absorbing layer 12 is grown by 3mum by a halide vapor-phase growing method on a semi-insulating InP substrate 11. An SiO2 film 14 is grown by a chemical vapor-phase accumulating method on the wafer, and with a photoresist as a mask the film 14 of the portion to form electrodes is removed with buffered HF. Then, with the photoresist and the film 14 as masks the layer 12 is etched. After etching, AgGeNi is deposited on the wafer, and the photoresist is removed with exfoliating solution. Then, the AuGeNi is removed except the recessed part. Finally, ohmic electrodes 13a, 13b are formed by heat treating in H2. Thus, since the distribution of the electric field intensity in the light absorbing layer can be reduced, the fall of a pulse response can be improved to obtain a photodetector having excellent responding characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photodetector using a semiconductor material.

[Conventional technology]

Currently, photodetectors made of semiconductor materials are used as photodetectors for converting optical signals into electrical signals in various optical systems.
-Diodes (PD) and avalanche photodiodes (APD) are widely used. In recent years, PC (Photob Coodu), which utilizes semiconducting phenomenon, has been
etive) The photodetector is high speed.

Due to its low noise, low voltage operation, and simple structure, it has attracted attention and is being actively researched.

FIG. 2 is a cross-sectional view showing the structure of a conventional PC photodetector, in which 1. An example of a 1 μm band zero device using G and A is shown. Semi-insulating I doped with Fe. n or i −1 to become a light absorption layer on the P substrate 11
flG, A, layer 12 is in liquid phase or gas phase.

A pair of ohmic conductors ff113a and 13b are grown on the InG and A layer 12 by the molecular beam epitaxial method.
, GeN1. These oats\1g of sex electricity! ! A bias is applied between the ohmic electrodes 13a and 13'b. If an optical signal to be detected is made incident on the G, A and layers 12, 1. Due to the photoconductive phenomenon in the G, A, and layers 12, an electric signal charged and converted between the ohmic electrodes 13a and 13b can be taken out.

[Problem that the invention seeks to solve]

When such a PC photodetector receives a high-speed pulsed optical signal, the rise of the response signal is several 100 ps.
It is very fast, about ec or less.

However, at the falling edge, a trailing effect of about several n5 ec occurs. The reason for this is that among the hole-electron pairs generated by light irradiation, the mobility of the hole is about 1/40 of that of the electron (I
In nG, A, the electron mobility step is 8000 smaller and 1
．． G, A, the electric field strength in the X direction that accelerates holes and electrons decreases in the thickness direction (X direction) in the light absorption layer 12 (Magazine [Applied Physics Letters (Ap
pl, t'bys, Letl), Volume 44, No. 1,
1984, pp. 99-101).

In other words, holes generated by light absorbed deep into the light absorption layer from the surface have low mobility and weak electric field strength for acceleration, resulting in a long transit time between the electrodes. , this appears as the basis of the response.

An object of the present invention is to solve such problems, improve the pulse response profile of a PC photodetector, and provide a photodetector with good response characteristics.

[Means for solving problems]

The structure of the present invention is a photodetector including a light absorption layer made of a semiconductor material formed on a semi-insulating semiconductor substrate, and a pair of ohmic electrodes formed on the light absorption layer.
A photodetector characterized in that a portion of the light absorption layer where the pair of ohmic electrodes are formed is thinner than other portions.

[Effect]

By adopting the electrode structure of the present invention as described above, the electric field strength that accelerates holes and electrons generated by light irradiation can be reduced compared to the case where an electrode is formed on a light absorption layer with a uniform thickness. Since the uniformity can be increased, the fall of the response can be improved.

This will be explained using FIG. 3. Figure 3 (a>,
(b) shows the electrode 1 of the PC photodetector according to the conventional method and the present invention.
3 (C).

(d) shows a distribution diagram of the electric field strength in the X direction in the depth direction of the light absorption layer in the conventional method and the present invention. The light irradiated onto this PC photodetector penetrates into the absorption layer by a penetration depth d according to the absorption coefficient of the light absorption layer and is absorbed.

FIG. 3 (In the case of a>, let the interval between the electrodes 13a and 13b be W, and the bias voltage applied between these electrodes be ■),
In the first approximation, the electric field strength in the X direction at a depth X from the surface is expressed as V/(w+2x). In other words, the electric field strength decreases from the surface to the inside (FIG. 3(C)).

On the other hand, as shown in FIG. 3(b), the electrodes 1.3a and 13b
d from the light absorption layer surface. If it is formed in a thinner area, the electric field strength in the X direction is V/(w+21Xd
ol), which is maximum at the position x=do.

Here, as an example, assuming dO=d/2, the minimum value of the electric field strength in the X direction in the range of O<x×d is V, / (W+2 d ) in the case of Fig. 3(c), Fig. 3 In case (d), V
/(w+d), and the uniformity of the electric field strength is higher in the case of the present invention shown in FIG. 3(d). The fall of the pulse response is determined by the transit time between the electrodes of the holes generated by light irradiation, which are accelerated by the weakest electric field.
By increasing the uniformity of the electric field strength in this way, the falling response can be improved. - [Example] The present invention will be explained in detail below with reference to Examples.

FIG. 1 is a sectional view illustrating an embodiment of a photodetector according to the present invention. First, the manufacturing method of this embodiment will be explained. Here, 1μm of TnGaAs/InP material is used.
A strip material detector is shown.

Semi-insulating I. P substrate 11 (Fe doped, resistivity P≧10
1, G by the hydride vapor phase epitaxy method on
, As light absorption layer 12 (n-type carrier concentration <1× Si0□14 film formed by chemical vapor deposition (CVD) method, Sibley MP-13007O) ~ Portion where electrodes are to be formed using resist as a mask 810□ is removed by buffered HF.

Next G, In using photoresist and Sho□ as a mask.
The GaAs light absorption layer 12 is etched. This work...l
For ching, H, PO4: )120□:H20=1:
A 1:3 mixed solution was used, and the etching depth was 0.75 μm, which is about half of the light penetration depth (~1.5 μm). After etching, Au
When GeNi is deposited and the photoresist 1-MP-1300 is removed using a stripping solution, the AuGe
Ni is removed (lift-off method). Finally, ohmic electrodes 13a and 13b were formed by heat treatment in H2. Note that the thickness of 5i02 was set in advance so that it would serve as an AR coating film for incident light, and it was not specifically removed.

In the device manufactured here, the electrode spacing is 5 μm, but when a voltage of 5 μm is applied between the electrodes 13a and 13b, the minimum electric field applied to the holes generated within the penetration depth from the surface Assuming a mobility of 7.7 KV/Ω-/'v5, the transit time between the electrodes is about 400 psec.

On the other hand, when there is an ohmic electrode on a light absorption layer with a uniform thickness as usual, the transit time of a hole is about 640 p.
sec, the response characteristics are greatly improved. Furthermore, the degree of this improvement becomes even greater when the distance between the electrodes becomes approximately the same as the penetration depth of light due to the miniaturization of the electrodes.

In the production of this example: 1. , G, A, a liquid phase method, a molecular beam epitaxial method, or an organometallic method can be used to grow the layer. In addition, in this example, the material is 1°G5As/
Although the InP system is used, the present invention is not limited to this (it is obvious that it can also be applied to Ga^IAs/GaAs systems, etc.).Also, the conductivity type of the light absorption layer may be p type, but p A shape is more effective. Also, as for the shape of the electrode, a comb-shaped electrode is desirable because it can make the area of the light-receiving part isotropic and large.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to reduce the electric field intensity distribution in the light absorption layer, so that it is possible to improve the fall of the pulse response and to obtain a photodetector with excellent response characteristics.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the photodetector according to the present invention, FIG. 2 is a sectional view showing the configuration of a conventional photodetector, and FIGS. 3(c) and 3(d) are distribution diagrams of the y-direction electric field strength in the depth direction of the light absorption layer of the conventional and the present invention. , 11...Semi-insulating 1nP substrate, 12...I
nGaAS layer, 13a, 13b...-ohmic electrode, 14...5102.

Claims (1)

[Claims] In a photodetector consisting of a light absorption layer made of a semiconductor formed on a semi-insulating semiconductor substrate and a pair of ohmic electrodes formed on this light absorption layer, the pair of ohmic electrodes are formed. A photodetector characterized in that the thickness of the light absorption layer in the portion where the light absorption layer is exposed is thinner than in other portions.