JPH0226082A - Photodiode - Google Patents

Abstract

PURPOSE:To achieve reduction in the capacity without substantially lowing sensitivity by forming a third electrode of a second conductive type formed at the same potential as for a first electrode in the periphery of the second electrode. CONSTITUTION:A second electrode 5 of a second conductive type ohmic electrode is formed smaller on a light-absorbing layer 2 with respect to a light- receiving surface A. In the periphery of this, a third electrode of a second conductive type is annually formed. A first electrode 4 of a first conductive type ohmic electrode is formed in the lower part of the substrate 1. Carriers generated by the light which enters the light-receiving surface A are distributed by an electric field biased in an opposite direction by the second conductive type ohmic electrode 5 and the third electrode 6, and the second conductive type ohmic electrode 5 and the first conductive type ohmic electrode 4. As mentioned above, capacity exists between the electrode 5, and the third electrode 6 and the electrode 4. However, since the area ratio of the electrode 5 in the light-receiving surface A is small, the capacity can be made smaller while the light-receiving sensitivity is almost maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention relates to a photodiode including a first electrode formed on the back surface and a second electrode formed on the top surface.

[Conventional technology]

A photodiode generates electrons and
A pair of holes occurs. The generated carriers are distributed by the electric field of the junction biased in the opposite direction and extracted as a current. Photodiodes are used in many applications because they have relatively fast response times, high efficiency, and operate at low voltages.

Among them, the pin photodiode is excellent in high-speed operation because the capacitance can be reduced due to the presence of the i-layer, and the travel time of carriers in the depletion layer can be shortened by applying a high voltage.

FIG. 3 shows the structure of a conventional pin photodiode. FIG. 3(a) is a cross-sectional view seen from a direction perpendicular to the light incident direction, and FIG. 2(b) is a plan view seen from the light incident direction. InP of the first conductivity type (e.g. n-type)
An i-type InGaAs light absorption layer 2 is formed on a substrate 1 such as the above.

On this light absorption layer 2, Ga of the second conductivity type (for example, p type) is formed.
A crystal growth layer 3A made of InAs is formed. Furthermore, a ring-shaped second conductivity type ohmic electrode 3 is formed on this crystal growth layer 3A, and a light-receiving surface A is formed inside the second conductivity type ohmic electrode 3 (
(See figure (b)). Furthermore, a first conductivity type ohmic electrode 4 is formed at the bottom of the substrate 1. When light enters the light-receiving surface A of this photodiode, holes and electrons are generated in the light-absorbing layer 2, which operates as a light-receiving element.

[Problem to be solved by the invention]

However, the photodiode according to the prior art has a drawback that the capacitance is large because the area of the second conductivity type ohmic conductor t33 to which voltage is applied is large, and high speed performance is poor.

Note that since the capacitance is determined by the light-receiving area, the capacitance can be reduced by reducing the light-receiving area. However, since the light-receiving sensitivity of the photodiode itself also decreases at the same time, it has been difficult to construct a photodiode with high speed and good light-receiving sensitivity.

Therefore, an object of the present invention is to provide a photodiode with excellent high-speed performance without reducing sensitivity.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a photodiode that includes a first electrode of the first conductivity type formed on the back surface and a second electrode of the second conductivity type formed on the light receiving surface (top surface), which is connected to earth. A third electrode of a second conductivity type is formed around the second electrode.

As this third electrode, a ring-shaped electrode of the second conductivity type centered at the formation position of the second electrode can be used.

[Effect]

Since the present invention is configured as described above, the capacitance in the photodiode can be reduced by the action of the third electrode provided around the second electrode. Also,
Since the area ratio of the second electrode on the light receiving surface is extremely low,
There is virtually no reduction in the light receiving area.

〔Example〕

An embodiment of a photodiode according to the present invention will be described below with reference to the accompanying drawings. In the description, the same elements are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 1 shows an embodiment of a photodiode according to the present invention. FIG. 3(a) is a cross-sectional view seen from a direction perpendicular to the light incident direction, and FIG. 2(b) is a plan view seen from the light incident direction.

The difference from the conventional technology is that the ring-shaped second
The conductive type ohmic electrode 3 is configured to have a small area ratio on the light receiving surface, and the third electrode of the second conductive type, which is connected to the ground, is formed in the shape of a ring, for example.

On the substrate 1 such as InP of the first conductivity type (for example, n-type),
A light absorption layer 2 made of i-type InGaAs or the like is formed. On this light absorption layer 2, a second conductivity type ohmic electrode (second electrode) 5 is formed to be smaller than the light receiving surface A (
For example, a third electrode 6 of the second conductivity type (or the first conductivity type) is formed in a ring shape around the second conductivity type ohmic electrode 5 (about 1 μm for a light receiving diameter of 80 μm). Further, a first conductivity type ohmic electrode (first electrode) 4 made of AuZn or the like is formed at the bottom of the substrate 1. 1st
The conductive type ohmic electrode 4 and the third electrode 6 are connected to ground, and the second conductive type ohmic electrode 5 is applied with a predetermined voltage. Carriers generated by the light incident on the light-receiving surface A are moved between the second conductivity type ohmic electrode 5 and the third conductivity type ohmic electrode 6, and between the second conductivity type ohmic electrode 5 and the first conductivity type ohmic electrode due to an electric field biased in the opposite direction. Sorted by 4. In this case, capacitance exists between the second conductivity type ohmic electrode 5, the third electrode 6, and the first conductivity type ohmic electrode 4;
Since the area ratio on the light-receiving surface A is reduced, the capacitance can be reduced while substantially maintaining the light-receiving sensitivity. In this case, since the first conductivity type ohmic electrode 4 and the third electrode 6 are configured at the same potential, no capacitance is generated.

Note that the size, shape, number, position, etc. of the third electrode are not limited to those in the above embodiment. What is important is that the light-receiving surface is formed by a third electrode having the same potential as the first electrode formed on the back surface, and a small second electrode is formed inside the light-receiving surface.

Further, when the second conductivity type ohmic electrode 5 is configured to be p-type and the light absorption layer 2 is configured to be i-type, p-type Ga is provided between the second conductivity type ohmic electrode 5 and the light absorption layer 2.
A crystal growth layer made of InAs may be formed. In this case, since the electrode is formed on the p-type crystal growth layer, contact resistance can be reduced.

FIG. 2 is a plan view (viewed from the light incident direction) showing a modification of the photodiode according to the present invention. Same figure (
a) shows arms 6 a s 6 b extending toward the center (second electrode 5) inside the third electrode 6 formed in a ring shape.
,... 61 are provided. This arm 6as6
bs... 61 is configured to be as thin as possible, so that the light receiving sensitivity does not decrease.

In the same figure (b), the third electrode 6 is formed in a rectangular shape, and the second electrode 5 is formed in the center thereof. The same figure (C) is
The third electrode 6 is formed into a comb-teeth shape and placed on both sides of the second electrode 5. Note that the tooth portion extending to the light-receiving surface A is formed thin to prevent a decrease in light-receiving sensitivity. The figure (d) shows two 2nd '21! The poles 5a and 5b are juxtaposed, and the third electrode 68% 6 b % 6 is placed between them.
c is placed. Note that the central portion of the third electrode 6b is formed to be thin so that the light receiving sensitivity does not decrease. In FIG. 5E, the second electrode 5 is formed into an elongated shape, and U-shaped third electrodes 6a and 6b are arranged on both sides of the second electrode 5 so as to surround it. In FIG. 1F, the second electrode 5 of the photodiode shown in FIG. 1 is eccentric. According to this photodiode, the center area where the light intensity is highest can be used as the light receiving surface.
Effective use of incident light can be achieved.

Note that the distance between the second electrode and the third electrode in the above embodiment is configured to be larger than the distance between the first electrode and the second electrode. Therefore, the capacitance between the second and third electrodes is much smaller than the capacitance between the first and second electrodes and can be ignored.

Next, experimental results comparing the prior art and the present invention will be shown. This experiment compared the capacitance and sensitivity of a photodiode according to the prior art and a photodiode according to the present invention (see FIG. 1). The light receiving diameter of each was 80 μm, and the outer diameter of the second electrode 5 of the photodiode according to the present invention was 1 μm. The capacitance of the photodiode according to the prior art was 2 pF, but the capacitance of the photodiode according to the present invention was 0.05 pF, which made it possible to significantly reduce the capacitance. In this case, the sensitivity of the photodiode according to the prior art was 0.75 A/W, and the sensitivity of the photodiode according to the present invention was 0.7 A/W, and the decrease in sensitivity was slight.

〔Effect of the invention〕

Since this invention is configured as explained above,
Capacity can be lowered without substantially reducing sensitivity. Therefore, a photodiode with good sensitivity and high speed can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the photodiode according to the present invention, FIG. 2 is a plan view showing a modified example of the photodiode according to the present invention, and FIG. 3 is a diagram showing a photodiode according to the prior art. FIG. 1...Substrate 2...Light absorption layer 3.5...2nd conductivity type ohmic electrode 4...1st conductivity type ohmic electrode 6...3rd electrode Patent applicant Agent of Sumitomo Electric Industries, Ltd. Patent Attorney Haseyo Yoshikima
Mountain 1) Row photodiode Fig. 1゛----)-m-' Modified example Fig. 2 (2) Modified example Fig. Prior art Fig. 3

Claims (1)

[Claims] 1. A photodiode comprising a first electrode of a first conductivity type formed on a back surface and a second electrode of a second conductivity type formed on a light receiving surface (top surface), wherein the first electrode A photodiode characterized in that a third electrode of a second conductivity type having the same potential as the second electrode is formed around the second electrode. 2. The third electrode is arranged so that the distance between the second electrode and the third electrode is significantly larger than the distance between the first electrode and the second electrode. 1. The photodiode described in 1. 3. The photodiode according to claim 1, wherein the third electrode is formed in a ring shape with the second electrode at the center.