JPS6025280A - Avalanche photo diode type light-receiving element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION +a+ Technical Field of the Invention The present invention relates to a light receiving element for optical communication, and particularly to enhancement of the guard ring effect in a leaf-shaped light receiving element.

(Background of BL technology In optical communications using optical fibers, avalanche filter diode (ADP) type photodetectors are used as high-sensitivity photodetectors, especially for long-distance communications. A low concentration impurity diffusion region of the same conductivity type as the high concentration impurity diffusion region, that is, a guard ring is provided around the high concentration impurity diffusion region on the surface.This causes uniform avalanche multiplication to occur in the semiconductor layer below the light receiving surface. , the quantum efficiency can be high.

(C1 Prior art and problems) However, in conventional ADPs, when the applied reverse voltage is increased, breakdown tends to occur at the corners around the guard ring. This breakdown occurs extremely irregularly. , which causes noise, i.e.
The guard ring is effective in eliminating the occurrence of breakdown at the corners of the high concentration diffusion region on the light receiving surface and generating uniform avalanche multiplication, but its own breakdown voltage (Vg) is The breakdown voltage (
There is no large difference compared to νa), and as a result, when data Va is applied to ADP, breakdown begins in a part of the guard ring section, causing noise. For this purpose, A
There was a drawback that the high sensitivity characteristic peculiar to DP could not be fully utilized.

(d1 Purpose of the Invention The present invention provides a P-type light-receiving element with a sufficient multiplication factor by making the breakdown voltage Va in the semiconductor layer below the light-receiving surface smaller than the breakdown voltage Vg in the guard ring part. The present invention aims to provide a high-sensitivity light-receiving element suitable for long-distance optical four-wave transmission.

te1 Structure of the Invention The present invention is characterized in that the impurity concentration in the layer thickness direction of the light absorption layer is changed in two stages in a four-leaf type light receiving element. It is characterized by having a low density in the part far from the light-receiving surface.

(') Embodiments of the Invention Below, embodiments of the present invention will be explained with reference to the drawings.
/ InGaAs1 InGaAs P-based heterojunction light receiving element was taken as an example, but the same applies to 5iADP and the like.

FIG. 1 shows an example of the present invention, InP/InG.
FIG. 2 is a schematic diagram of a cross section of an aAs/1nGaAsP-based light receiving element, for example, an r+'-In P substrate 1 (lEg #
1.35 eV), an InGaAs layer 2 (Eg
'0.75 eV, thickness 1.5-3 μm), InGaA
s P layer 3 (Eg=0.90eV, thickness 0.5-0.
8 μm), n-InP layer 4 (Eg″j1.35e
y-1nP layer 5 and guard ring 6+ (p type) are formed on the upper surface layer of n-1nP layer 4 by diffusing Zn or the like.

Here, the InGaAs layer 2 acts as a 1 μm band light absorption layer, and the p□-1nP layer 5 acts as a light entrance window.

Therefore, InGaAs P Pi 3 and n-InP
I'ti4 and p''-InP layer 5 are both InGa
A material with a smaller energy gap than the As layer 2 is used. The InGaAs P layer 3 is provided for the purpose of creating a stepwise barrier between the InGaAs layer 2 and the n-InP layer 4 to facilitate the movement of holes and to increase the response speed of the device.

By the way, in the device of the present invention, InGaAsFm
The impurity concentration in the thickness direction of 2 is changed in two steps as shown in FIG. In Figure 2, the vertical axis shows InGaAs.
Layer 2 - Depth measured from the 1nGaAs P layer 3 interface x)
, the impurity concentration is plotted on the horizontal axis. That is, InGa
At the depth from the interface of the As layer 2 to Xl, the impurity concentration is as high as about 5 x 1016 cm-3, and from x1 to the total depth x2, IX as in normal ADP.
The concentration is set to be as low as IQ''cm'. It is easily possible to provide such a concentration distribution during epitaxial growth of InGaAs1M2.

In FIG. 1, when the InG, aAs layer 2 has the impurity concentration distribution as described above, when a reverse voltage is applied between the r+'-InP substrate 1 and the r-1nPFtS side as the negative electrode, V- The depletion layer extending from the 1nP layer 5 is InG
It is blocked up to the interface between the aAs PIN 3 and the InGaAs layer 2. , which means that the X of the InGaAs layer 2 is O
This is because the region from xl to xl has a high impurity concentration.

Generally, the thickness of the depletion layer 1) and the electric field strength (F) are
The relationship is approximately as shown in the figure, and the breakdown voltage (Va) is proportional to the area surrounded by the F axis, the t axis, and the curve C. In the conventional P, IXl016cm-3 is uniformly distributed over the entire InGaAs layer 2, and the depletion layer spreads over the entire region of the InGaAsfii 2 in the thickness direction. In this case, the electric field strength distribution of the depletion layer is curve C
If so, the element of the present invention will have a curve C1, and the breakdown voltage (Va) will be reduced by Δνa corresponding to the area of the shaded area.

Note that in InGaAs1i 2, from x1 to x
Although the region up to 2 does not directly contribute to avalanche multiplication, it acts as a light absorption layer, so the quantum efficiency of the device does not change.

Furthermore, although generally the diffusion rate of carriers decreases as the impurity concentration increases, since this region is maintained at a low impurity concentration, the frequency characteristics of the element will not be impaired.

As described above, in the light receiving element according to the present invention, the breakdown voltage of the light receiving surface is reduced, and as a result, the guard ring effect is normally exhibited. That is, stable avalanche multiplication with a large multiplication factor is performed in the semiconductor layer below the light-receiving surface, making it possible to provide the light-receiving element with high sensitivity and low noise.

Note that, as described above, the present invention is applicable to In
P/InGaAs1 InGaAs P-based photodetector, but also DP using other single composition semiconductors.
AD consisting of type elements or other combinations of semiconductors
It is clear that the invention is also applicable to P-type elements.

(g+Effect of the Invention According to the present invention, the guard ring effect is enhanced by reducing the breakdown voltage of the light-receiving surface of a P-type light-receiving element, making it possible to provide a high-sensitivity, low-noise light-receiving element. effective.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a cross-sectional structure of a light-receiving element according to the present invention, which is explained in detail, FIG. 1 is a diagram showing an impurity concentration distribution in a light absorption layer of the light-receiving element, and FIG. FIG. 3 is a diagram for explaining reduction in breakdown voltage of a light receiving surface. In the figure, 1 is a 0''-InP substrate, 2 is InGaAs
layers, 3 is InGaAs PN, 4 is n-InPJi,
5 is ps-1nPJ"#, and 6 is a guard ring.

Claims (1)

[Claims] An ADP type light-receiving element characterized in that the impurity concentration in the layer thickness direction of the light-absorbing layer is high in a portion close to a light-receiving surface and low in a portion far from the light-receiving surface.