JPS6018975A - Semiconductor light-receiving element - Google Patents

Abstract

PURPOSE:To obtain the light-receiving element having the withstand voltage design with leeway and also having no reflected light coming back to the source of light by a method wherein the light-receiving surface of an avalanche photodiode chip is attached to the stem by providing the desired angle on the incident light. CONSTITUTION:The chip attaching surface of the stem is inclined at the angle theta against the incident light hnu, and the chip is fixed on the inclined surface. The light hnu which is made incident on the light-receiving surface 10 at the angle theta proceeds diagonally in an ApD element and reaches in InGaAs. At this time, the thickness (d) down to the layer 3 is effectively increased to d/costheta. Accordingly, the distance passing through a depletion layer is increased too, and a pair of electron and hole generated by the light absorption at the upper part of the layer 3 can be obtained by having a sufficient field accelerating effect on a shallow depletion layer 41. Through these procedures, the increase in withstand voltage can be prevented by extending the depletion layer deeply, and the thickness and the density of an epitaxial layer is designed with leeway. Also, the light reflected by the light-receiving surface does not return to the light source, and the unstable state of optical oscillation mode of the light source can be prevented.

Description

Detailed Description of the Invention (11) Technical Field of the Invention The present invention relates to a semiconductor light-receiving element for optical communications, particularly an avalanche photodiode (avalanche photodiode).
Attachment of a chip formed with a diode+hereinafter abbreviated as APD to the stem relates to improvement of the angle.

(2) Background of the technology APD applies a reverse voltage to a pn junction to form a high electric field region (depletion layer) adjacent to it, and this high electric field accelerates carriers chemically converted by incident light. This is a semiconductor photodetector that obtains a large photocurrent by utilizing the avalanche phenomenon caused by collision ionization between C and bound carriers.

Figure 1 is a cross-sectional view of a heterostructure AI'D formed from an indium-phosphorus (InP)/indium-gallium-arsenic-phosphorus (InGaAsP)-based compound semiconductor, in which 1 is an n+ type InP semiconductor substrate, 2 is n-type InP M
, 3 is n-type 1nGaAsJ! which becomes the light absorption layer. Or I
nGaAsP III, 4 becomes the multiplication layer 1] type In
The P layer is formed by epitaxial growth. Further, numeral 5 is an oxide film for surface protection, 6 and 7 are electrodes, 8 is a diffusion layer, and 9 is an oxide film for preventing electric field concentration at the end of the diffusion layer 8 and for uniform multiplication. A guard ring made of a p-swelled diffusion layer is shown, and the breakdown voltage of this guard ring 9 is higher than the lateral pressure under the p+ diffusion layer 8.

When a reverse high voltage is applied such that the electrode 6 has a positive polarity and the electrode 7 has a negative polarity in a PD having such a structure, a depletion layer 11 is formed below the p+ diffusion layer 8 and extends into the InGaAs 1ia in a triangular shape.

The light hν incident on the light-receiving surface 10 is mainly caused by the depletion 1it
ll to generate electron-hole pairs. The generated photocarriers are accelerated by the electric field in the depletion layer 11 and fljl electrically impact the bound carriers of the crystal atoms, causing an avalanche phenomenon. In this way, a large photocurrent can be obtained from a small primary current, that is, a high light-receiving sensitivity can be obtained.

By the way, photocarriers generated outside the depletion layer 11, after moving to the depletion layer 11 by diffusion, contribute to the avalanche phenomenon described above. Therefore, if a large number of photocarriers are generated outside the depletion layer 11, it takes time for diffusion, which causes a slow response speed of the light receiving element. Therefore, the depletion layer 11 is made of In as much as possible.
Extending the field deeply into the GaAs layer 3 to enhance the electric field acceleration effect is required to obtain a fast response speed.

However, if the depletion layer is made deeper, the breakdown voltage of the depletion layer 11 increases and the breakdown voltage difference with the guard ring 9 decreases, resulting in a drawback that the effect of the guard ring 9 becomes weaker.

From the above, in an APD, it is necessary to make the withstand voltage in the depletion layer under the light-receiving surface lower than the withstand voltage in the guard ring region, and to generate electron-hole pairs due to light absorption in the depletion layer. Ru.

(3) Prior Art and Problems The semiconductor depth on which the conventional APD is formed is arranged on the stem 22 so that the incident light hv is perpendicular to the light-receiving surface, as shown in FIG. Note that the chip 21 is attached to the stem 22 by a conventional technique such as soldering, and the reference numeral 23 in the figure indicates the wiring connected to the electrode ^110.

With this arrangement, the incident light can reach InGaAs at the shortest distance.
N3 and generates electron-hole pairs not only on the top of InGaAsJFf3 but also inside it. Therefore, in conventional APDs, it is required to form a depletion layer that extends deeply, but as the depletion layer extends deeply, the withstand voltage increases.
There is a problem in that there is no margin for design values such as the thickness of the epitaxial layer and the carrier concentration, making it difficult to design withstand voltage.

Furthermore, since the light hv that is perpendicularly incident on the light receiving surface returns to the light source after being reflected, there is also the problem that it makes the oscillation mode of the laser light emitting element unstable.

(4) Purpose of the invention In view of the problems of the prior art described above, the object of the present invention is to provide a semiconductor light-receiving element that does not require a deep depletion layer, has sufficient voltage resistance design, and prevents reflected light from returning to the light source. shall be.

(5) Structure of the invention and this object according to the invention
) A semiconductor light-receiving element is formed by attaching a semiconductor chip formed with a diode to a stem, and the semiconductor chip is attached to the stem at an angle so that the light-receiving surface of the avalanche photodiode forms a desired angle with respect to incident light. This is achieved by providing a semiconductor light-receiving element characterized by the following.

(6) Examples of the invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a side view of the stem 32 with the chip 31 attached. As shown in the figure, when the chip is attached to the stem, the incident light hv
The chip is attached to this inclined surface by, for example, solder.

Due to the structure of the stem 32 described above, the light hν is transmitted to the chip 31.
The light enters the light-receiving surface of the APD formed above at an incident angle deviated from the conventional vertical direction by an angle θ.

FIG. 4 is a partial cross-sectional view of eight PDs showing the path of the incident light having the above-mentioned angle θ, and in this figure, the same parts as in FIG. 1 are designated with the same reference numerals.

The light hν incident on the light receiving surface 10 at an angle θ is APD
It travels diagonally inside and reaches InGaAsm 3, but because it travels a longer distance than if it were incident perpendicularly, the effective layer thickness increases, and the thickness d up to InGaAsJN 3 is larger than this (d/cos θ) become.

Therefore, as the distance traveled within the depletion layer increases, the InGa
A sufficient electric field acceleration effect can be obtained in the shallow depletion layer 41 in which electron-hole pairs are generated due to light absorption in the upper layer of As 3 .

In this way, it is possible to avoid an increase in breakdown voltage due to extending the depletion layer deeply, so it is possible to have leeway in the epitaxial layer thickness and carrier concentration in breakdown voltage design, and the effect of the guard ring and fast response speed can be fully utilized. Become so. Note that the inclination angle θ of the chip is determined as appropriate depending on the characteristics of the convex circle.

Further, according to the present invention, the light reflected by the light-receiving surface out of the incident light does not return to the light source again as in the conventional case, so that the problem of unstable optical oscillation mode of the light source is also solved.

(7) Effects of the Invention As explained in detail above, according to the present invention, parameters such as the epitaxial layer thickness and carrier concentration related to the design of a semiconductor photodetector, especially the breakdown voltage design, can be determined within a comfortable range. Therefore, there is a negative effect on the yield rate in the production of light receiving elements. Further, according to the present invention, reflected light on the light receiving surface of the element does not return to the light source, which is highly effective in reducing noise in the light emitting device.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing the structure of an avalanche photodiode-1'' (APD), Fig. 2 is a side view of the stem showing how the chip with the PD formed above is attached to the stem in the conventional manner, and Fig. 3 is a side view of the stem. The figure is a side view of the stem showing the state in which the chip is installed according to the present invention, and Figure 4 is a side view of the stem showing the state in which the chip is attached according to the present invention.
FIG. 3 is a partial cross-sectional view of the APD showing light absorption in the PD. 1-n+ type 1nP semiconductor substrate, 2-n type InP layer, 3-
n-type 1nGaAs layer, 4-n-type 1nP layer, 5-oxide film,
6. 'l-electrode, 8-/p+ diffusion layer, 9-guard ring, 10-light receiving surface, LL 41.42-depletion layer 21, 31
-1 Semiconductor chip, 22.32-Stem, 23-Wiring patent Applicant: Fujitsu Limited Figure 1 Figure 2 Figure 4

Claims (1)

[Claims] A semiconductor light-receiving element is formed by attaching a semiconductor chip formed with an avalanche photodiode to a stem, and the semiconductor chip is attached to the stem at an angle such that the light-receiving surface of the avalanche photodiode forms a desired angle with respect to incident light. A semiconductor light-receiving element characterized by being attached.