JPH0411787A - Semiconductor light receiving device - Google Patents

Abstract

PURPOSE:To enhance a yield and to prevent a decrease in a quantum efficiency by forming an insulator and a multilayer film reflector of semiconductor on a semiconductor substrate, and reflecting a light in a direction of a light absorption layer. CONSTITUTION:A semiconductor substrate 2 has a pair of main surfaces 3, 4, a light receiving surface 5 formed on one surface 3, and a light absorption layer 1 formed therein. When a light hpsi incident on the surface 5 is not absorbed to the layer 1, but arrived at the other surface 4, a multilayer film reflector 6 reflects the light toward the layer 1. The reflector 6 is formed by alternately laminating an insulator layer 7 and a semiconductor layer 8 on the surface 4 of the substrate 2. Thus, the layer 1 improves to absorb the light, its yield is improved, and a decrease in a quantity efficiency can be prevented.

Description

[Detailed Description of the Invention] [Regarding the general semiconductor light receiving device, the object of the present invention is to provide a semiconductor light receiving device with a high device yield and high-speed response characteristics without a decrease in quantum efficiency due to a decrease in reflectance. a semiconductor substrate having a surface and a light absorption layer therein; a light-receiving surface formed on one main surface of the semiconductor substrate; and a light-receiving surface formed on one main surface of the semiconductor substrate; A multilayer formed on the other main surface of the semiconductor substrate, in which insulator layers and semiconductor layers are stacked alternately, so that when the light reaches the other main surface, the light is reflected in the direction of the light absorption layer. and a membrane reflector.

[Industrial application field] The present invention relates to a semiconductor light receiving device.

In optical communication using optical fibers, semiconductor modulators and semiconductor photodetectors that operate at high speed are used.6If the communication wavelength is in the 1 μm band (1.3 μm band, 1.5 μm band, etc.), most of the semiconductor photodetectors are ,] is formed using a compound semiconductor heterostructure using nP as a substrate.

[Conventional Technique #f] With the progress of development, optical communication has come to mainly use light with a wavelength of 1 to 16 μm. Along with this, 1 to 1
．． There is a demand for a semiconductor photodetector with excellent high-speed characteristics at a wavelength of 6 μm.

Generally, as the wavelength of light becomes longer, the absorption coefficient of light of a semiconductor becomes smaller. For this reason, in conventional semiconductor light receiving devices, it has been necessary to increase the thickness of the light absorption layer in order to obtain a certain quantum effect. However, when the light absorption layer was made thicker, high-speed response could not be achieved due to the delay caused by carrier transit time.

Therefore, while limiting the thickness of the light absorption device to a certain value or less,
Attempts have been made to improve the high-speed response of semiconductor photodetectors.

FIG. 5 shows an example of a semiconductor photodetector according to the prior art.
On the n medium-sized xnp substrate 52, a 1n GaAS layer and an In
A multilayer reflector 6 is formed by repeating the P layer, and an n-type InGaAs light absorption layer 51 is formed thereon.
Further, an n-type 1nP window layer 63 is formed on the 6 surface, and a P-type diffusion region 59 in which Zn is diffused into the n-type region is formed so as to reach the light absorption layer 51. Therefore, a ρn junction is formed around this p'' type Zn diffusion region 59.The light receiving surface has a ρn junction with a controlled thickness.
An s S i N antireflection film 55 is formed, and an SiN bancivation film 64 is formed on the outside thereof.

The surrounding part of the p'-type Zn diffusion region 55 is exposed, and a pfllll layer consisting of a Ti layer, a PT layer, and an Au layer is formed on top of the exposed part.
An I electrode 62 is also formed. On the back surface of the board 52, there is a
n f! made of an alloy of u-Ge-Ni! An I electrode 61 is formed. In this structure, when light enters from the light receiving surface, it passes through the Zn diffusion regions 55 in three of the six InP window layers, enters the nGaAs light absorption layer 51, and is absorbed. The unabsorbed light is InGaA3nGaA
It is reflected by a multilayer film reflector 56 formed with three light absorption surfaces 51,
It goes upward, that is, it passes through the 5InGaAs light absorption layer 51 again. When the InGaAsnGaAs light absorption layer 1 is formed, electron-hole pairs are formed and current flows through the diode.

In the side path shown in Figure 5, a multilayer film reflector is provided directly below the light absorption layer, so the unabsorbed light is reflected and enters the light absorption layer again, increasing the efficiency of light utilization. .

FIG. 6 shows an example of another semiconductor light receiving device according to the prior art. An n-type 1nGaAS light absorption layer 51 and an n-type 1nP window layer 63 are formed on an n-type 1nP substrate 52, and an n-type 1nP window layer 63 is formed from the surface. A p'' type Zn diffusion region 59 is formed by diffusing Zn into the region.Si is formed on the surface of the Zn diffusion region 59.
A N antireflection film 55 is formed, and around it a Ti layer and a PT
layer, p1 consisting of a stack of Au layers! ! 1 t [i 6
2 is formed. In addition, SiN is placed around the light receiving surface.
A bancivation film 64 is also formed.

In FIG. 6, a reflector is not formed in the semiconductor structure. Therefore, the light that is not absorbed by the 1nGaAs light absorption layer 51 out of the light incident from the top surface is absorbed by the I nGaAs light absorption layer 51.
The light passes through the nP substrate 52 and reaches the bottom surface of the substrate. In the side path of FIG. 6, Si02
A reflector is formed consisting of layer 67 and six Au layers above it. Therefore, the light reaching the lower surface of the substrate is reflected by the reflector and directed upward.Since no electrodes can be formed in the portion where the five reflectors are provided, an n-side type [i61] is formed around it.

In the case of the structure III shown in Fig. 6, the incidence is from above, and the InG
a^^ The light not absorbed by the absorption layer 51 is transferred to the substrate 52.
After reaching the bottom surface, the light is reflected again and goes upward, increasing the efficiency of light utilization.

7. Problems to be Solved by the Invention] According to the conventional technique shown in FIG. 5, hetero semiconductor layers made of different materials are epitaxially laminated on a substrate to form a multilayer film reflector. Due to the need for lattice matching, there are material limitations.

For example, when using InP and InGaAs, it is not possible to obtain a large 6M refractive index ratio with refractive index values such as 2°99 and 3.43, so it is necessary to increase the number of calendars, and the two types of layers are It is necessary to laminate ~50 layers. As a result, the number of heterointerfaces increases, making it easier for crystal defects to occur, which causes a decrease in device yield.

In the conventional technique shown in FIG. 6, a gold reflective film is used to increase the reflectance, or if the gold layer is directly formed on the semiconductor substrate, the reflectance may be lost during the heating process. For this reason, a silicon oxide film is first formed on the substrate, and then a gold layer is formed on top of it, but the gold layer peels off due to poor adhesion between the silicon oxide film and the gold layer.
This tends to cause a decrease in reflectance, which causes a decrease in quantum efficiency.

As described above, conventional semiconductor light receiving devices have problems such as low device yield and low quantum efficiency.

An object of the present invention is to provide a semiconductor light-receiving device with high device yield and high-speed response characteristics without a decrease in quantum efficiency due to decrease in reflectance.

Means to solve the 5 issues] FIG. 1 is a diagram explaining the principle of the present invention.

A semiconductor substrate 2 having a pair of main surfaces 3.4 and having a light absorption layer 1 therein constitutes a main part of a semiconductor light receiving device. A light receiving surface is formed on one main surface 3 of the semiconductor substrate 2, and a multilayer film reflector 6 is formed on the other main surface 4. The multilayer reflector 6 is formed by laminating an insulator layer 7 and a semiconductor layer 8 in an alternately stacked manner.

Light incident on the light receiving surface 5 from above is absorbed by the light absorption layer 1. The unabsorbed light reaches the other main surface 4,
There, the light is reflected by the multilayer film reflector 6 and the light absorbing layer 1 is reflected again.
Head in the direction of.

The other main surface 4 may be processed into a convex shape and a multilayer film reflector may be formed thereon.6 Also, one main surface 3 may be processed into a convex shape and a light-receiving surface may be formed thereon. .

[Function] By forming the multilayer film reflector 6 with the insulating layer 7 and the semiconductor layer 8, a large refractive index ratio can be obtained. As the refractive index ratio increases, the reflectance at each interface between the insulating layer 7 and the semiconductor layer 8 increases, which is the sum of these. Totally reflected light (indicated by an arrow in the figure) also easily increases. For this reason, the number of layers of the multilayer film reflector is small, and there is no need to form the multilayer film reflector on the surface of the semiconductor substrate and grow a semiconductor crystal on it, so there is no need for lattice matching, etc. The material of the insulator layer semiconductor layer can be selected from many substances.

When the other main surface is processed into a convex shape and a multilayer film reflector is formed thereon, a concave mirror is formed within the semiconductor, and light is reflected with a focusing effect. Therefore, reflected light can be efficiently focused on the light absorption layer.

By processing one main surface 3 into a convex shape and forming the light-receiving surface 5 into the curved surface, a semiconductor convex lens is formed, and incident light can be efficiently focused on the light absorption layer.

3 Embodiment J FIGS. 2(A), 2(B), and 2(C) show a semiconductor light receiving device according to an embodiment of the present invention.

FIG. 2(A) shows a circuit configuration of a semiconductor light receiving device, in which a light receiving diode D is directly reverse biased through a resistor R from ataE. The voltage across the terminals of resistor R is applied to amplifier A. When no light is incident on the photodiode D, the photodiode E is in an off state and no current flows. At this time, the voltage across the resistor R1' becomes zero.

When light is incident on the light receiving diode D, S-son/hole pairs are generated, and a current I flows through the reverse bias diode D. This current I generates a signal voltage of V=IH across the resistor, and the amplifier A amplifies the signal voltage.

The light receiving diode D shown in FIG. 2(A) is as shown in FIG. 2(B).
It has the configuration shown in . An n-type 1nGaAs light absorption layer 11 is formed on an n+-type 1nP substrate 12, and an n-type 1nP window layer 23 is formed thereon. Zn is diffused from the surface of the window layer 23 to form a p-type Zn diffusion region 1.
9 are formed to constitute a diode. TnGaAsn
The thickness of the GaAs light absorption layer 1 is approximately 1 μm, and the wind layer 23 thereon is, for example, 1 μm thick. Also, Z
The n-diffusion region 19 is formed to extend from the window layer 23 into the light absorption layer 11, for example, to a depth of about 012 μm. After forming the light receiving diode structure, the back surface of the substrate 12 is etched to a thickness of, for example, about 140 μm. S i N with a selected thickness on the surface of the Zn diffusion region 19
M is deposited to form a SiN antireflection film 15. Also,
The surface around the Zn diffusion region is exposed, and Ti1l is deposited on top of it.
, Pt1J! The Au layer on one surface forming the laminated P-side electrode 22 made of an Au film has a thickness of, for example, 2 to 3 μm. Further, a SiN passivation film 24 is formed on the surface other than the light receiving surface. The main part of the light incident from the light-receiving surface is absorbed by the light-absorbing layer 11, or a part of it is transmitted through the light-absorbing layer 11 and re-absorbs the light as it travels through the substrate 12. One multilayer film reflector is formed facing the light-receiving surface so as to reflect light onto the light receiving surface. The multilayer reflector 16 is formed, for example, from alternating layers of SiO2 layers 17 and amorphous Si layers 18, as shown in FIG. 2(C). SiO2 is an insulator with a refractive index of approximately 1.46, and amorphous Si
is a semiconductor with a refractive index of about 35. In this way, a low refractive index nL and a high refractive index nH are obtained. By using insulators and semiconductors that have such a large refractive index ratio, a multilayer reflector can have a reflectance of approximately 96% with each layer consisting of two layers as shown in the figure.
becomes. A multilayer film reflector composed of an insulator and a semiconductor generally has a large refractive index ratio between the insulator and the semiconductor, so a high reflectance can be obtained even if the number of overlapping of each layer is reduced. Furthermore, it is easy to select a material that has good adhesion to the base as the insulator. The wavelength of the target signal light is 1.3
In the case of μm, the thickness of the SiO2 layer 17 is 2230 μm.
The thickness of the amorphous Si layer 18 is approximately 930 mm.
Select again. If the multilayer reflector 16 is formed below the light-receiving surface, an n-side electrode cannot be formed over it, so an n-side electrode 21 is formed around the periphery of the multilayer reflector 16 using, for example, Au Ge Ni 21 with a thickness of approximately 3000 mm. Formed with an alloy layer.

FIG. 3 shows the main parts of a semiconductor photodetector according to another embodiment of the present invention. In this embodiment, the lower surface of the substrate 12 is a convex curved surface, and a multilayer film reflector 16 is placed on the curved surface 26. is forming. The structure of the song is equivalent to the structure shown in FIG.

When the lower surface of the substrate 12 is made convex, a concave mirror is formed for light traveling inside the substrate. Therefore, when the light transmitted through the light absorption layer 11 reaches the concave mirror 26, it is reflected by the multilayer film reflector and condensed by the concave mirror. In this way, the reflected light can be efficiently collected on the light absorption layer 11 in the vicinity of the Zn diffusion region 19. In particular, the light utilization efficiency can be increased even for light incident from an oblique direction.

FIG. 4 shows a semiconductor light receiving device according to another embodiment of the present invention.

In this embodiment, the substrate 12 is placed on the upper side in the figure. An InGaAs light absorption layer 11 is formed on the lower surface of the substrate 12, and an InP window layer 23 is formed thereon. In addition, Znt dispersed region 19 from the surface of the lnP wind layer
is formed and reaches inside the light absorption layer 11.

In this embodiment, the light receiving surface 15 is formed on the surface of the substrate. The surface of the substrate is a convex curved surface 28, and SiN is deposited on it.
Anti-reflection film 1 is formed.

A pole 21 is formed on the n side around the convex force. A multilayer film reflector 16 is formed on the surface of the Zn diffusion region 19 shown in the lower part of the figure.The peripheral part of the Znt failure region is exposed, and a p-side film 22 is formed thereon to cover the multilayer film reflector 16. It is formed. The peripheral part of the ρ side electrode is a SiN passivation film 24.
covered with

In this embodiment, a semiconductor substrate 12 having a curved surface 28 is used.
A convex lens is formed by The incident light is condensed by this convex lens and enters the light absorber 11111. Therefore, compared to the light-receiving surface, the P-type is enlarged! The area of region 19 can be made small. It is suitable for reducing the capacitance C and resistance R associated with the diode structure and for high-speed operation.

Note that the light that is not absorbed when passing through the light absorption layer 11 once is reflected by the multilayer film reflector 16 provided on the lower surface, travels to the light absorption layer 11 again, and is absorbed there.

Note that since the thickness of the epitaxial crystal growth layer is sufficiently small compared to the thickness of the substrate, the reflected light enters the light absorption layer 11 again without being spread much, so that the utilization efficiency of the reflected light is also increased.

Note that the surface of the semiconductor substrate as shown in FIGS. 3 and 4 can be processed using wet etching, ion etching, or the like.

Although the present invention has been described above in accordance with the examples, the present invention is not limited thereto. For example, instead of InP and 1nGaAs as semiconductor materials, GaAs and Al are used as semiconductor materials.
Other materials such as GaAs-based materials and other materials such as SiN may be used instead of 5i02 as an insulator.

Effects of the Invention: As explained above, according to the present invention, the internal structure of the semiconductor substrate is relatively simple, and a multilayer reflector made of an insulator and a semiconductor is formed on the surface, thereby improving yield. Accordingly, it is possible to provide a semiconductor light-receiving device that has a high response speed and prevents a decrease in quantum efficiency.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the principle of the present invention, and FIGS.
A> is a circuit diagram of a semiconductor light receiving circuit, FIG. 2 (B) is a cross-sectional view showing the main parts of a semiconductor light receiving diode, and FIG. 2 (C) is a cross section showing the configuration of a multilayer film reflector provided in a semiconductor light receiving diode. 3, 4 are sectional views showing semiconductor light receiving devices according to other embodiments of the present invention, and FIGS. 5 and 6 are sectional views showing semiconductor light receiving devices according to the prior art. In the figure, 3.4 13.14 Light absorption layer Semiconductor substrate main surface Light-receiving surface Multilayer film reflector Insulator layer Semiconductor layer Semiconductor light-receiving diode Resistor DC power amplifier n-type 1nGaAs Light absorption layer n Medium-sized 1nP substrate main surface SiN Anti-reflection Multilayer film reflector SiO2 layer Amorphous St layer Zn diffusion region 9 0 side S pole P side electrode Curved surface (concave mirror) Curved surface (convex lens) Patent developer: Fujitsu Limited Agent: Patent attorney: Takashi Igeta - 2 others ) - / 1b 26: Curved surface (concave mirror) Fig. 3 1ζ 28 Bicurved surface (convex lens) Other examples Fig. 4 (A) Circuit (C) Multilayer film reflector? YV Figure 6

Claims (3)

[Claims] (1), a semiconductor substrate (2) having a pair of main surfaces (3, 4) and having a light absorption layer (1) therein; and one main surface (3) of the semiconductor substrate (2). a light-receiving surface (5) formed on the light-receiving surface (5); when light incident on the light-receiving surface (5) reaches the other main surface (4) without being absorbed by the light-absorbing layer (1), the light is transmitted to the light-receiving surface (5); An insulating layer (7) is provided on the other main surface (4) of the semiconductor substrate (2) so as to reflect the light in the direction of the light absorption layer (1).
) and a multilayer film reflector (6) formed by alternately stacking semiconductor layers (8). (2) The semiconductor light receiving device according to claim 1, wherein the other main surface (4) has a curved surface processed into a convex shape, and the multilayer film reflector is formed on the curved surface. (3) The semiconductor light receiving device according to claim 1, wherein the one main surface (3) has a curved surface processed into a convex shape, and the light receiving surface (5) is formed on the curved surface.