JPH11354827A - Photodetector and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the deterioration of a mesa type photodetector having a low-concn. active layer sandwiched between high-concn. layers on the interface/surface, by relatively thickening the peripheral part of the low-concn. layer than its central part. SOLUTION: The peripheral part of a low-concn. P buffer layer 13 is made thicker than its central part, resulting in a low electric field over an multiplying layer 16 and light absorption layer 14 at the peripheral part than that over the central part. As a result, the dark current flowing in the peripheral part and multiplication ratio of the peripheral part are suppressed to realize a high reliability, and the deterioration at the interface/surface of the main cause of deterioration of an avalanche diode can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light receiving element used for optical communication.

[0002]

2. Description of the Related Art Avalanche photodiodes (AP)
D), high reliability is required for communication light receiving elements such as PIN photodiodes. A structure with a planar guard ring shown in FIG. 1A has been known as a highly reliable APD. Incident light is absorbed by the P-InGaAs light absorbing layer 6, and the generated photocarriers are multiplied by the n-InP layer 4 by the voltage between the P-electrode 1 and the N-electrode 8. The electric field distribution of this element is as shown in FIG. In order to obtain good characteristics, the thickness of the multiplication layer is set to 0.1 by Zn diffusion 2.
Manage on the order of μm. In addition, by introducing a guard ring inclined junction formed by Be implantation or the like, peripheral yielding is suppressed, and high reliability can be achieved.

[0003]

On the other hand, Zn diffusion, Be
The implantation technique has a low manufacturing flexibility (<0.1 μm or less), and is not necessarily a desirable method from the viewpoints of simplification of the manufacturing process, easiness, and cost reduction.

An object of the present invention is to provide a simple, easy, and inexpensive element structure without impairing element characteristics and reliability, and a method of manufacturing the same.

[0005]

In order to achieve the above object, according to the present invention, in a mesa light receiving element having a structure in which both sides of a low-concentration active layer are sandwiched between high-concentration layers, the peripheral portion of the low-concentration layer has a center film thickness. Provide a structure that is relatively thicker than the part.

The principle of the present invention will be described with reference to an APD shown in FIG. In the structure shown in FIG. 2A, incident light is absorbed by the P ⁻ − light absorbing layer 14, and the injected electrons are multiplied by the low concentration multiplication layer 16. The gist of the present invention is to make the thickness of the P-low concentration buffer layer 13 thicker in the peripheral portion than in the central portion. As a result, as shown in the electric field distribution of FIG. 3B, the electric fields of the multiplication layer and the light absorption layer in the peripheral portion are smaller than those in the central portion. Therefore, the dark current flowing in the peripheral portion and the multiplication factor in the peripheral portion are suppressed, and as a result, high reliability can be realized. This is because deterioration at the interface and surface, which is a major factor of APD deterioration, can be suppressed.

[0007]

FIG. 2 shows a superlattice APD as an embodiment of the present invention. The principle of operation is as described above. Hereinafter, a manufacturing method will be described.

[0008] Undoped-InGaAs / In is deposited on an n-InP substrate 17 by molecular beam epitaxy.
AlAs multiplication layer (0.3 μm) 16, P-InAlAs high concentration buffer layer (P = 2 × 10 ¹⁷ , d = 0.2 μm) 1
5, P-InGaAs light absorbing layer (P = 2 × 10 ¹⁴ , d =
2 μm) 14, P-InAlAs low concentration buffer layer (P
= 2 × 10 ¹⁴ , d = 2 μm) 13 and a P-InAlAs high concentration buffer layer (P = 2 × 10 ¹⁸ , d = 2 μm) 12 were laminated.

Subsequently, a mesa structure was formed by wet etching, and a SiN passivation film 18 was formed by plasma CVD. After forming a contact hole in the center of the mesa, Zn is diffused into the hole to form a low concentration layer 1.
The central part of Sample No. 3 was partially concentrated. In this embodiment, the low-concentration residual film thickness was 0.1 μm. As a result of evaluating the characteristics of this element, the maximum bandwidth was 10 GHz and the gain bandwidth product was 80 GH.
Good characteristics of a dark current of 100 nA at z and a gain of 10 were obtained. In addition, a high-temperature constant-current conduction test at 200 ° C. and 100 μA was performed for reliability evaluation. From the results, an average element life of 100 years or more in continuous operation at 85 ° C. was estimated.

Further, the relationship between the thickness modulation value of the low-concentration layer 13 and the device reliability, which is the gist of the present invention, was examined. The thickness of the low-concentration layer 13 at the periphery is constant (2 μm), and the remaining thickness of the low-concentration layer at the center is 0 μm, 0.2 μm, 0.5 μm, and 1 μm.
As a result of examining the device of No. 0, 0.2 μm, 0.5
The estimated life is 100 years or more at 1 μm and 50-
80 years of results. From this, it was confirmed that the present invention was effective for improving the reliability.

FIG. 3 shows another embodiment in which the present invention is applied to a waveguide type PIN light receiving element. In this device, incident light enters from the end face of the device and is extracted as an electric signal from upper and lower electrodes. 21 is a P-electrode, 22 is a SiN passivation film, 23 is P-InGaAlAs (high concentration second cladding layer),
24 is P-InGaAlAs (high-concentration first cladding layer), 25 is P-InGaAlAs (low-concentration first cladding layer), 26 is P-InGaAs (light absorbing layer), 2
7 is N-InGaAlAs (high concentration first cladding layer),
28 is N-InGaAlAs (high-concentration second cladding layer), 29 is n-InP (substrate), and 30 is an N-electrode. The fabrication method is basically the same as in the above embodiment. By performing Zn diffusion in the central portion of the 25 P-low-concentration first cladding layer, the thickness of the low-concentration layer region in the central portion was made thinner than that in the peripheral portion (side surface and end surface) of 1 μm. In this element, as in the previous example, it was confirmed that high reliability (estimated life: 200 years) was achieved by the present invention.

[0012]

According to the present invention, a highly reliable light receiving element can be provided by a simple manufacturing method.

[Brief description of the drawings]

FIG. 1 is a sectional view and an electric field distribution diagram of a conventional APD with a guard ring.

FIG. 2 is a sectional view and an electric field distribution diagram of an APD according to an embodiment of the present invention.

FIG. 3 is a partial sectional perspective view of a waveguide type PIN-PD element according to one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... P- electrode, 2 ... Zn diffusion layer, 3 ... Be guard ring, 4 ... N-InP (multiplication layer), 5 ... N-InGaAs
P (electric field relaxation layer), 6 ... N-InGaAs (light absorbing layer), 7 ... N-InP (substrate), 8 ... N-electrode, 11 ...
P-electrode, 12 ... P-InAlAs (high concentration buffer layer), 13 ... P-InAlAs (low concentration buffer layer),
14 ... P-InGaAs (light absorbing layer), 15 ... P-In
AlAs (high concentration buffer layer), 16 ... undoped
-InGaAs / InAlAs (multiplication layer), 17 ... NI
nP (substrate), 18 ... SiN passivation film, 19
... N-electrode, 20 ... anti-reflection film, 21 ... P-electrode, 22
... SiN passivation film, 23 ... P-InGaAl
As (high concentration second cladding layer), 24 ... P-InGaAl
As (high concentration first cladding layer), 25... P-InGaAs
1As (low concentration first cladding layer), 26 ... P-InGa
As (light absorbing layer), 27 ... N-InGaAlAs (high concentration first cladding layer), 28 ... N-InGaAlAs (high concentration second cladding layer), 29 ... N-InP (substrate), 3
0 ... N-electrode.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Masato Shishikura 1-280 Higashi-Koigakubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory of Hitachi, Ltd. (72) Inventor Shinji Tsuji 1-280 Higashi-Koikekubo, Kokubunji-shi, Tokyo Hitachi Central Research Laboratory

Claims (9)

[Claims] In a mesa light receiving element having a structure in which both sides of a low-concentration active layer are sandwiched between high-concentration layers, the thickness of the low-concentration layer is zero at the center or at the periphery in the periphery compared to the center. A light-receiving element having a thick structure. 2. A mesa-type light receiving element having a structure in which both sides of a low-concentration active layer are sandwiched between high-concentration layers, wherein the thickness of the high-concentration layer is smaller at the periphery than at the center. A light receiving element characterized by the following. 3. A PIN photodiode having the element structure according to claim 1. 4. An avalanche photodiode having the element structure according to claim 1. 5. A waveguide photodiode having the element structure according to claim 1. 6. A light-receiving element according to claim 1, wherein the constituent layers include a high-concentration N-type layer, a multiplication layer, an electric field relaxation layer, a light absorption layer, a low-concentration P-type layer, and a high-concentration P-type layer. Wherein the light-receiving element is an avalanche photodiode in which a difference in film thickness between a central portion and a peripheral portion is caused by the low-concentration P-type layer and the high-concentration P-type layer. 7. The light receiving element according to claim 1, further comprising a light absorbing layer, a first cladding layer narrowing the light absorbing layer, and a second high-concentration cladding layer narrowing the light absorbing layer. A light receiving element wherein a difference in film thickness between a central portion and a peripheral portion is a waveguide photodiode provided by a low-concentration P-type layer and a high-concentration P-type layer formed in the first cladding layer. . 8. The light-receiving element according to claim 1, further comprising a step of forming a difference in film thickness between a central portion and a peripheral portion of said light-receiving element by Zn diffusion or Be ion implantation. How to create 9. An optical receiving module using the light receiving element according to claim 1.