JPS63211686A - Avalanche photodiode - Google Patents

Abstract

PURPOSE:To enable a fast response by providing a metal layer for light intercep tion on a protective film formed on a p<+>-type contact layer, p-type epitaxial layer, n<+>-type diffusion layer and the surface of an n<+>-type substrate except for the light receiving section to which an electric field is applied. CONSTITUTION:After forming a p-type epitaxial layer 2 on a n<+>-type Si sub strate 1, a recessed section 11 is formed by a mesa etching except for the part which is to become a photo detecting section, a diffusion is performed from the recessed part 11 to form a n<+>-type diffusion layer 4, and then a p<+> diffusion layer 5, a protective film 6 and an antireflection film 9 are formed. And finally, an anode electrode 7 and a metal layer 12 for light intercepting are formed simultaneously. Since the light incidence on the region other than the photo detecting section to which an electric field is applied is prevented by the metal layer 12 for light intercepting in this way, all the excited carriers generate only in the photo detecting section to which an electric field is applied and move at a high speed, exhibiting a fast response.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an avalanche photodiode (APD) that exhibits high-speed response.

[Conventional technology]

Conventional silicon avalanche photodiode (5)
(abbreviated as i-APD) is p''p as shown in Figure 2.
There is one with an n+ type planar mesa structure.

In this Si'-APD, after forming a p-type epitaxial layer 2 on an n+-type Si substrate 1, a mesa groove 3 is provided, and an n+ diffusion layer 4 is formed on the inner wall of the mesa groove 3. p+ type diffusion layer5. Protective film6. Anode electrode7. The cathode electrode 82 is obtained by forming the antireflection film 9.

In the 5i-APD, carriers (electrons) with a high ionization rate can generally be injected into the avalanche region, and if the excitation of optical carriers within the avalanche region can be reduced, multiplication noise can be reduced. For this purpose, as shown in FIG.
The pn junction 10 may be formed at a deep position from the surface, and the p+pn+ type is an advantageous structure for low noise characteristics.

In addition, in the planar mesa structure, an n+ type diffusion layer 4 is formed along the inner wall of the mesa groove 3, and the end of the pn junction 10 is covered with a protective film 6 on the main surface, resulting in high reliability. That's what you get.

5i-AP with such a p+pn+ planar mesa structure
When light is incident on D and a reverse voltage is applied, the p-type epitaxial layer 2 becomes a depletion layer, carriers are excited in the depletion layer by the incident light, and electrons as excited carriers form a p-n junction. It is injected into the avalanche multiplication region near 1o, ionization collision occurs, and a multiplication effect is obtained. As the applied voltage increases, the electric field strength within the depletion layer increases, the ionization rate increases, and the carrier multiplication effect becomes significant.

Furthermore, as the applied voltage is increased, the multiplication effect further increases, resulting in a state in which a reverse current suddenly flows. This state is called avalanche breakdown, and this voltage is the breakdown voltage.

In this way, S i -A P D has a multiplication gain inside the element due to the carrier multiplication effect, and a high multiplication gain can be obtained when a voltage close to the breakdown voltage is applied.

Further, in this case, a high electric field is applied within the light absorption layer, and the excited carriers move at high speed, so that the light absorption layer has high-speed response characteristics.

[Problem that the invention seeks to solve]

In the conventional Si-APD as described above, it is unavoidable that light enters the light receiving part other than the light receiving part where the antireflection film 9 is formed, and during operation, the p-type epitaxial layer 2 of the light receiving part , the excited carriers generated here move at high speed because they are depleted and an electric field is applied.
Since no electric field is applied to areas other than the light-receiving part, the excited carriers move at low speed due to diffusion. Therefore, there was a problem that the response speed decreased.

This invention was made to solve these problems, and is an APD that exhibits high-speed response. ! The purpose is to obtain.

[Means for solving problems]

The APD according to the present invention has p
A light-shielding metal layer is provided on a protective film formed on the surface of a + type contact layer, a p type epitaxial layer, an n + type diffusion layer, and an n + type substrate.

[Effect]

In this invention, light enters the semiconductor layer under the light-shielding metal layer other than the light-receiving area where the electric field is applied, and no excited carriers are generated, and the excited carriers generated at the light-receiving area where the electric field is applied are accelerated by the electric field. Moving.

〔Example〕

FIG. 1 is a diagram showing the structure of an embodiment of the APD of the present invention.

In this figure, the same symbols as in Fig. 2 indicate the same parts,
11 is a recess formed by mesa etching; 12 is a recess formed by mesa etching;
For example, it is a light-shielding metal layer made of Aj or the like.

Next, the manufacturing process of the APD of this invention will be explained.

First, a p-type epitaxial layer 2 is formed on an n+-type Si substrate 1, and then a recess 11 is formed by mesa etching except for a portion that will become a light receiving section. Next, diffusion is performed from this recess 11 to form an n+ type diffusion layer 4, and then a p+ type diffusion layer 5.
．． A protective film 6P and an antireflection film 9 are formed. At this time, the protective film 6 consists of a p+ type diffusion layer 5p, a p type epitaxial layer 2. n+ type diffusion layer 4 and n+ type Si
Formed on substrate 1. Finally, the anode electrode 7 and the light-shielding metal layer 12 are simultaneously formed using photolithography. However, at this time, the light-shielding metal layer 12 protects the area where no electric field is applied i! It is formed on the film 6 so as not to contact the conductive portion of the semiconductor layer.

That is, in the APD of the present invention, as is clear from FIG. 1, the light-shielding metal layer 12 prevents light from entering areas other than the light-receiving area where the electric field is applied, so that all of the excited carriers are not exposed to the electric field. It is generated only at the light receiving part and moves at high speed. Therefore, the APD of this invention exhibits fast response.

Moreover, since the light-shielding metal layer 12 is formed so as not to be electrically conductive with the semiconductor layer and the anode electrode 7,
The response speed is not decreased by increasing the electrode capacitance.

〔Effect of the invention〕

As explained above, this invention excludes the light-receiving part to which an electric field is applied.
Since a light-shielding metal layer is provided on the protective layer formed on the surface of the type diffusion layer and the n+ type substrate, light is prevented from entering areas other than the light receiving area where the electric field is applied. Excited carriers are generated and these excited carriers move at high speed due to the electric field, which has the effect of enabling high-speed response.

Furthermore, since the formation of the light-shielding metal layer can be performed simultaneously with the formation of the anode electrode, it is possible to construct the APD without making it expensive.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of an embodiment of the APD of the present invention,
FIG. 2 is a diagram showing the structure of a conventional S i -APD. In the figure, 1 is an n + type Si substrate, 2 is a p type epitaxial layer, 4 is an n + type diffusion layer, 5 is a p + type diffusion layer, 6 is a protective film, 7 is an anode electrode, 8 is a cathode Ti pole, 9 is a reflection In the prevention film, 1o is a pn junction, 11 is a recess formed by mesa etching, and 12 is a light-shielding metal layer. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] a p-type epitaxial layer formed on an n^+-type substrate;
A p^+ type contact layer formed on a partial region of the surface of the p type epitaxial layer, and an n^+ type contact layer formed from the outer peripheral surface of the p type epitaxial layer to the n^+ type substrate.
The above p^+ excluding the ^+ type diffusion layer and the light receiving part where the electric field is applied
type contact layer, said p type epitaxial layer, said n^
An avalanche photodiode having a planar mesa structure comprising a + type diffusion layer and a protective film formed on the surface of the n^+ type substrate, characterized in that a light shielding metal layer is provided on the protective film. Avalanche photodiode.