JPH10270741A - Semiconductor photoreceptor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor photoreceptor operating at a high speed over a wide frequency band. SOLUTION: A semiconductor photoreceptor 10 with a light incidence plane has a semi-insulating substrate 12. InP buffer layer 14 with 0.5 μm film thickness, n-InP electrode contact layer 16 with 0.5 μm film thickness, i-InP carrier transition layer 18 with 0.3 μm film thickness, i-InGaAs light absorption layer 20 with 0.3 μm film thickness, and n-InP cap layer 22 with 0.2 μm film thickness which form a semiconductor structure laminated in this order on the substrate 12. The cap, light absorption, carrier transition and electrode contact layers of the foregoing layers are processed to constitute a mesa structure. On the cap and electrode contact layers 22, 16, p- and n-side electrodes 24, 26 are formed respectively. Further, on the region of the mesa structure and on the region of the surface of the electrode contact layer 16 wherefrom the electrode 26 is excluded, a silicon nitride film 28 is formed. The portion present inside the p-side electrode 24 is a circular light reception plane 30 with an antireflection film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light receiving device, and more particularly to a semiconductor light receiving device excellent in high-speed operation over a wide band.

[0002]

2. Description of the Related Art In an optical communication system in which an electric signal is converted into an optical signal by a light emitting element, an optical signal is received by a light receiving element via an optical fiber, and the received optical signal is converted into an electric signal, a high speed and high speed communication system is required. Efficient operating characteristics are required for light emitting elements and light receiving elements. In particular, in a future high-speed and large-capacity optical communication system, a semiconductor light receiving element (Photo Diode) excellent in high-speed operation over a wide band is indispensable.

[0003]

In the case of the pin type semiconductor light receiving element, the response speed of both the surface incident type and the waveguide type light receiving element depends on the length of the traveling time during which the carrier travels through the depletion layer. The frequency characteristics depend on the magnitude of the CR time constant of the light receiving element. That is, the shorter the running time,
The faster the response speed of the light receiving element and the smaller the CR time constant, the wider the frequency band of the light receiving element. However, when the depletion layer is made thinner to shorten the carrier transit time in order to increase the response speed, the junction capacity increases due to the thinned depletion layer, and the CR time constant becomes large. The shape of the light receiving element limits the band. Therefore,
Conventionally, it has been difficult to realize a light receiving element having excellent high-speed operation over a wide band.

Accordingly, an object of the present invention is to provide a semiconductor light receiving element which operates at high speed over a wide band.

[0005]

As described above, when the depletion layer is simply thinned to avoid carrier traveling delay,
The band of the light receiving element is limited in a trade-off manner. Therefore, the present inventor has paid attention to the fact that the drift speed of holes is about one digit lower than the drift speed of electrons, which is a factor of carrier traveling delay. To simply shorten the hole transit time, the light absorbing layer may be thinned. However, there are many problems such as an increase in CR time constant and a decrease in light receiving sensitivity. And a carrier traveling region, and an optical signal absorption region is provided with a light absorbing layer smaller than the energy of light received by the band gap as an optical signal absorbing region. As a carrier traveling region, the light absorbing layer is in contact with the light absorbing layer and the band gap receives light. A carrier traveling layer which is larger than the energy of light and simply allows electrons from the light absorbing layer to travel is provided. The thickness of the light absorbing layer was made thinner than that of the conventional light absorbing layer, and the sum of the thicknesses of the light absorbing layer and the carrier traveling layer was made larger than the thickness of the conventional light absorbing layer. Thereby, the junction capacitance is defined by the sum of the thicknesses of the light absorption layer and the carrier transit layer, and becomes smaller, so that the CR time constant becomes smaller. On the other hand, as described below, no carrier running delay occurs. This is because electrons having a high drift speed travel through the light absorption layer and the carrier traveling layer, and holes having a low drift velocity travel only through the thin light absorption layer. In this way, the carrier running delay time can be shortened while keeping the CR time constant small, and the trade-off between the carrier running delay and the CR time constant can be satisfied.

Based on the above-mentioned knowledge obtained, in order to achieve the above object, a semiconductor light receiving element according to the present invention comprises at least a light absorption layer and a semiconductor electrode contact layer electrically contacting an n-side electrode. In a semiconductor light receiving element having a semiconductor laminated structure having a semiconductor layer, a semiconductor layer having a band gap wider than the energy of light to be received and having a carrier concentration substantially equal to that of the light absorbing layer is used as a carrier traveling layer as a light absorbing layer and a semiconductor electrode. It is characterized in that it is provided in contact with the contact layer on the light absorbing layer. According to the present invention, the carrier transit layer is formed of a material having a band gap larger than the energy of the received light and a high electron drift speed.

[0007] Preferably, the light absorption layer is formed of a laminated structure of semiconductor layers having different band gaps, and the carrier traveling layer is formed so that a built-in electric field for accelerating the traveling of holes is formed in the light absorption layer. The band gap is made larger in a layer closer to. In addition, the light absorbing layer is formed of a laminated structure of semiconductor layers having different carrier concentrations, and a layer closer to the carrier traveling layer is formed so that a built-in electric field for accelerating hole transport is formed in the light absorbing layer. Ensure that the concentration is high. As a result, the response speed is increased and the frequency band is widened. Further, preferably,
A stacked structure forming a light absorbing layer is formed so as to have a gradient (graded) band gap or carrier concentration.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the case where light having a wavelength of 1.3 .mu.m or 1.55 .mu.m, which is usually used for optical communication, is to be absorbed, preferably, the light absorption layer is made of InGaAs or InG.
aAlAs or InGaAsP is used, and InP is used for the carrier transit layer. When the light absorbing layer is formed into a graded band gap, the band gap is reduced as the distance from the carrier transit layer increases so that a built-in electric field is generated for holes. In addition, in order to form a built-in electric field in the light absorbing layer in accordance with the carrier concentration gradient, the carrier concentration may be reduced if the n-type light absorbing layer is used as the distance from the carrier traveling layer increases, p
The carrier concentration may be increased if the light absorption layer is of a mold type. Alternatively, the conductivity type may be changed from n-type to p-type as the distance from the carrier transit layer increases. Hereinafter, embodiments of the present invention will be described specifically and in detail with reference to the accompanying drawings and examples.

[0009]

Embodiment 1 This embodiment is an embodiment having a basic structure of a semiconductor light receiving element according to the present invention. FIG. 1 is a schematic cross section showing a layer structure of the semiconductor light receiving element of Embodiment 1. FIG. Semiconductor light receiving element of this embodiment (hereinafter simply referred to as light receiving element) 10
Is a surface incident type light receiving element, as shown in FIG.
A layer thickness of 0.5 formed on a substrate 12 of semi-insulating InP and the substrate 12 by an epitaxial crystal growth method sequentially.
μm InP buffer layer 14, 0.5 μm thick n-I
nP electrode contact layer 16, i-In having a layer thickness of 0.3 μm
P carrier running layer 18, i-InGa having a thickness of 0.3 μm
It has a semiconductor laminated structure of an As light absorbing layer 20 and an n-InP cap layer 22 having a layer thickness of 0.2 μm.

The band gap and carrier concentration of each semiconductor layer are as follows. Buffer layer 14: Band gap / 1.35 eV Carrier concentration / 1 × 10 ¹⁷ cm ⁻³ Electrode contact layer 16: Band gap / 1.35 eV Carrier concentration / 1 × 10 ¹⁹ cm ⁻³ Carrier running layer 18: Band gap / 1 .35 eV light absorbing layer 20: band gap / 0.74 eV cap layer 22: band gap / 1.35 eV carrier concentration / 1 × 10 ¹⁹ cm ⁻³

In the semiconductor laminated structure, the cap layer 22,
The upper layers of the light absorption layer 20, the carrier traveling layer 18, and the electrode contact layer 16 are processed into a mesa structure. A p-side electrode 24 is formed on the cap layer 22 which is the uppermost layer of the mesa structure, and an n-side electrode 26 is formed on the electrode contact layer 16. Has a silicon nitride film 28 formed as a protective layer and an antireflection film. The inside of the p-side electrode 24 is a circular light receiving surface 30 having a diameter of 20 μm and having an antireflection film 28.

Hereinafter, an outline of a method for manufacturing the light receiving element 10 of the first embodiment will be described. First, a buffer layer 14, an electrode contact layer 16, and a carrier traveling layer 1 are sequentially formed on a substrate 12.
8. Epitaxial crystal growth of the light absorption layer 20 and the cap layer 22. Next, the etching mask is patterned using a known lithography technique, and wet etching is performed with an etching solution using the obtained etching mask as a mask to form an upper layer of the cap layer 22, the light absorbing layer 20, and the carrier traveling layer 18. Is etched to form a mesa structure of the surface incident type light receiving element. Next, the protective film 2
8, the electrodes 24, 26, etc. are formed, and the surface incident type light receiving element 1
Complete 0.

Embodiment 2 This embodiment is an embodiment of a semiconductor light receiving element according to the present invention, and FIG. 2 schematically shows a main part of a layer structure of the light receiving element of Embodiment 2. ing. Light receiving element 4 of this embodiment
0 indicates that the light absorbing layer 20 is made of the i-InGaAs of Example 1.
s instead of the bulk layer, a band gap of 0.77 eV and a layer thickness of 0.15
μm of the lower light absorbing layer 42 made of InGaAlAs and 0.15 μm of In
The upper light-absorbing layer 44 made of GaAs has a two-layer structure in which each of the upper light-absorbing layers 44 is epitaxially grown.
2 is formed on the carrier traveling layer 18 so as to be in contact with the carrier traveling layer 18. The light receiving element of the second embodiment is
Except for the structure of the light absorbing layer 20, it has the same configuration as the first embodiment.

Embodiment 3 This embodiment is an embodiment of a semiconductor light receiving element according to the present invention, and FIG. 3 schematically shows a main part of a layer structure of the light receiving element of Embodiment 3. ing. Light receiving element 5 of this embodiment
0 indicates that the light absorbing layer has a carrier concentration of 1 × 10 ¹⁵ cm ⁻³ and a layer thickness of 0 so that a built-in electric field is generated for holes instead of the i-InGaAs bulk layer of Example 1. .15
a lower light absorption layer 52 made of n-InGaAs of μm;
Carrier concentration is 5 × 10 ¹⁷ cm ^-3 and layer thickness is 0.15 μm
The upper light-absorbing layer 54 made of n-InGaAs has a two-layer structure formed by epitaxial crystal growth, and the lower light-absorbing layer 52 is formed on the carrier traveling layer 18 so as to be in contact with the carrier traveling layer 18.

Conventional Example In order to make a comparison with the semiconductor light receiving element according to the present invention, the carrier transit layer 18 of the first embodiment has the same i-type as the light absorbing layer 20.
The light absorbing layer 20 having a thickness of 0.6 μm is used as the InGaAs layer.
A light receiving element having the same configuration as the light receiving element 10 of the first embodiment, that is, a light receiving element having a conventional configuration was manufactured as a conventional example except that the above-described configuration was adopted.

The 3 dB reduction band for the modulated light signal having a wavelength of 1.55 μm was measured for the light receiving elements of Examples 1 to 3 and the conventional light receiving element.
Bands of z, 45 GHz, 48 GHz and 23 GHz were obtained. From the above results, it can be seen that the light receiving elements of Examples 1 to 3 have a wider band than the conventional light receiving elements and are suitable for high-speed and large-capacity light transmission.

While one of the embodiments of the present invention has been described above, the present invention may be configured as a waveguide type light receiving element in which a clad layer for confining light above and below a light absorbing layer and a carrier transit layer is formed. it can. Further, since the light absorption layer and the carrier transit layer form a hetero interface, a heterojunction spike is formed in the conduction band, and there is a concern that a potential well associated therewith adversely affects device characteristics. In that case, it goes without saying that modifications such as providing a graded region so as to smoothly connect the band gaps can be made.

[0018]

According to the present invention, there is provided a semiconductor light receiving device having a semiconductor laminated structure having at least a light absorbing layer and a semiconductor electrode contact layer electrically contacting an n-side electrode.
Furthermore, a semiconductor layer having a band gap wider than the energy of the received light and having a carrier concentration substantially equal to that of the light absorbing layer is in contact with the light absorbing layer between the light absorbing layer and the semiconductor electrode contact layer as a carrier traveling layer. By providing such a structure, the carrier transit time is shortened while keeping the CR time constant small, and a semiconductor light receiving element excellent in high-speed operation over a wide band is realized.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a layer structure of a light receiving element according to a first embodiment.

FIG. 2 is a schematic cross-sectional view illustrating a main part of a layer structure of a light receiving element according to a second embodiment.

FIG. 3 is a schematic cross-sectional view illustrating a main part of a layer structure of a light receiving element according to a third embodiment.

[Explanation of symbols]

 Reference Signs List 10 light receiving element of Example 1 12 semi-insulating InP substrate 14 0.5-μm thick InP buffer layer 16 0.5-μm thick n-InP electrode contact layer 18 18-μm thick i-InP carrier traveling layer 20 I-InGaAs light absorbing layer having a thickness of 0.3 μm 22 n-InP cap layer having a thickness of 0.2 μm 24 p-side electrode 26 n-side electrode 28 silicon nitride film 30 circular light receiving surface 40 light receiving element of the second embodiment 42 lower light Absorbing layer 44 Upper light absorbing layer 50 Light receiving element of Example 3 52 Lower light absorbing layer 54 Upper light absorbing layer

Claims (3)

[Claims] 1. A semiconductor light receiving device having a semiconductor laminated structure having at least a light absorbing layer and a semiconductor electrode contact layer electrically contacting an n-side electrode, having a band gap wider than the energy of light to be received. A semiconductor layer having a carrier concentration substantially equal to that of the light absorbing layer is provided as a carrier transit layer between the light absorbing layer and the semiconductor electrode contact layer and in contact with the light absorbing layer. element. 2. The light absorbing layer is formed of a laminated structure of semiconductor layers having different band gaps from each other, and is close to the carrier traveling layer so that a built-in electric field for accelerating holes is formed in the light absorbing layer. 2. The semiconductor light receiving device according to claim 1, wherein the band gap is larger in the layer. 3. The light absorbing layer is formed of a laminated structure of semiconductor layers having different carrier concentrations from each other, and is close to the carrier traveling layer so that a built-in electric field for accelerating hole traveling is formed in the light absorbing layer. 2. The semiconductor light receiving device according to claim 1, wherein the carrier concentration is higher in the layer.