Active solid-state devices (e.g. – transistors – solid-state diode – Heterojunction device – Light responsive structure
Reexamination Certificate
2000-12-11
2002-06-04
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Heterojunction device
Light responsive structure
C257S021000, C257S022000, C257S028000
Reexamination Certificate
active
06399968
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor photoreceiving device that is suitable for use in optical communications and performs opto-electric conversion of light at high speeds, and more particularly to a semiconductor photoreceiving device that can selectively extract a signal of long wavelength light in multiplexed optical communications (especially with two wavelengths).
This application is a counterpart application of Japanese application Serial Number 212945/2000, filed Jul. 13, 2000, the subject matter of which is incorporated herein by reference.
2. Description of Related Art
In general, light of wavelengths 1.3 &mgr;m and 1.55 &mgr;m is used as the optical signal in optical communications, especially flat mounted optical modules. In optical integrated circuits, this 1.3 &mgr;m and 1.55 &mgr;m optical signal is present as multiplexed light. Accordingly, it is necessary that the photoreceiving device be an element that can selectively receive both 1.3 &mgr;m optical signals and 1.55 &mgr;m optical signals.
Conventionally, the photoreceiving devices that selectively receive optical signals with wavelengths of 1.3 &mgr;m (hereinafter referred to as short wavelength) are provided with a light-absorbing layer composed of InGaAsP with a band gap wavelength of about 1.4 &mgr;m. However, the light-absorbing layer generally has the property of absorbing light with wavelengths shorter than the band gap wavelength of the light-absorbing layer. Accordingly, it is very difficult to form a light-absorbing layer that can receive only an optical signal of 1.55 &mgr;m (hereinafter referred to as long wavelength) in a single layer.
Consequently, the method of interposing an optical filter between the multiplexed light entering the photoreceiving device and the photoreceiving surface of the photoreceiving device has been used for the selective reception of long wavelength optical signals, as disclosed in the Reference
1
(Ishigami et al., “Automatic Machine For Bonding Fiber Block To Planar Lightwave Circuit”, 1998 Institute of Electronics, Information and Communication Engineers, Electronics Society Conference C-3-87), Reference
2
(Hashimoto et al., “1.3/1.55 &mgr;m WDM optical module for full duplex operation using PLC platform”, 1998 Institute of Electronics, Information and Communication Engineers, Electronics Society Conference C-3-110), and Reference
3
(Maeda et al., “WDM by multilayered dielectric filter on silica based waveguide (
3
)”, 1998 Institute of Electronics, Information and Communication Engineers, Electronics Society Conference C-3-150).
As another method for the selective reception of long wavelength optical signals, the inventors of the present invention previously proposed a semiconductor photoreceiving device disclosed in Reference
4
(Japanese Unexamined Patent Pubication No. 2000-77702). The semiconductor photoreceiving device in Reference
4
comprises a first light-absorbing layer and a second light-absorbing layer in that order within an optical path for multiplexed light; wherein this first light-absorbing layer is composed of a material with a band gap wavelength longer than 1.3 &mgr;m and shorter than 1.55 &mgr;m (for example, InGaAsP), and the second light-absorbing layer is composed of a material having a band gap wavelength longer than 1.55 &mgr;m (for example, InGaAs). Shorter wavelength light is thereby absorbed by the first light-absorbing layer and long wavelength light that passes through this first light-absorbing layer is absorbed by the second light-absorbing layer.
However, in the case of using an optical filter with the object of selectively receiving long wavelength light, it becomes necessary to perform a process of making a recess on the waveguide of the optical integrated circuit (PLC: planar lightwave circuit) in order to insert the optical filter. This results in a high insertion loss for the optical waveguide, increases PLC processing costs, and results in relatively high part costs for the optical filter.
In a photoreceiving device comprising a first light-absorbing layer and a second light-absorbing layer, the first light-absorbing layer must be thick so that the selection ratio of short wavelength light to long wavelength light is the desirable selection ratio for the photoreceiving device. As a result, there is high stress between the first light-absorbing layer and the layers formed on top of the first light-absorbing layer, and there is a risk of strain occurring in each layer formed on top of the first light-absorbing layer. Also, the first light-absorbing layer is formed by epitaxial growth; the cost of the photoreceiving device increases in proportion to the thickness of the epitaxial layer.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a photoreceiving device used in multiplexed optical communications including short wavelength light and long wavelength light for selectively receiving long wavelength light, that is inexpensive and has good properties, without cutting away the PLC waveguide and inserting an optical filter.
In order to achieve this object, the present invention is to provide a semiconductor photoreceiving device having the following constitution for selectively receiving long wavelength light from multiplexed light including long wavelength light and short wavelength light. Specifically, this semiconductor photoreceiving device comprises a multilayered film of alternately stacked layers of materials having mutually different indexes of refraction. The thickness of each layer and the number of layers in the multilayered film are designed such that long wavelength light is transmitted and short wavelength light is reflected by the multilayered film. The photoreceiving device further comprises a first light-absorbing layer that is composed of a material having a band gap wavelength longer than the long wavelength light. Also, the photoreceiving device has a structure such that multiplexed light enters the first light-absorbing layer through the multilayered film.
When multiplexed light comprising long wavelength light and short wavelength light enters this multilayered film, the short wavelength light is reflected by the multilayered film and the long wavelength light passes through the multilayered film and reaches the light-absorbing layer. The long wavelength light can thereby be selectively absorbed, or received, by the light-absorbing layer. Therefore, it is unnecessary to insert a conventional optical filter requiring a cutting operation, between the photoreceiving device and the incoming multiplexed light. Consequently, problems arising from establishing the optical filter (PLC processing costs, optical filter costs, optical waveguide insertion loss) are avoided.
This type of semiconductor photoreceiving device preferably comprises a substrate having a first main surface and a second main surface; the first light-absorbing layer may be established on the first main surface side of the substrate and the multilayered film may be established on the second main surface side of the substrate.
When the photoreceiving surface for the multiplexed light is assumed to be the second main surface side of the substrate, and the first main surface of the substrate is referred to as the top surface, while the second main surface is referred to as the back surface, the semiconductor photoreceiving device having this type of constitution is referred to as a back surface incidence (or entry) type photoreceiving device.
The semiconductor photoreceiving device may also be constituted such that the substrate has a first main surface and the multilayered film is established on the first main surface side of the substrate with the first light-absorbing layer interposed therebetween.
A photoreceiving device with such a constitution is referred to as a top surface incidence (or entry) type photoreceiving device in contrast to the abovementioned back surface incidence type photoreceiving device.
In these back surface incidence type and top
Furukawa Ryozo
Kato Masanobu
Ngo Ngan V.
Oki Electric Industry Co. Ltd.
Wenderoth, Lind & Ponak, L.L.P.
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