Superlattice Buffer Layer for Leakage Suppression in Photodiodes
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Solution Overview
Problem
High-speed avalanche photodiodes for optical communication face issues with leakage current due to mutual diffusion between Fe and Zn, leading to inadequate separation of diodes and reduced light-receiving sensitivity, especially when multiple diodes are formed on a semi-insulating InP substrate.
Innovation Solution
A semiconductor light-receiving device is designed with a buffer layer composed of a superlattice alternately laminating InP and AlxGayIn1-x-yAs layers, which suppresses leakage current and maintains light-receiving sensitivity by creating an energy barrier and preventing light absorption in the wavelength band used for optical communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick undoped InP buffer layer is grown to separate the substrate from the p-type contact layer, then leakage current is suppressed, but light-receiving sensitivity deteriorates due to light absorption in the buffer layer
Solution Approach 1:
The buffer layer is segmented into multiple thin layers with different compositions (InP layers and AlGaInAs layers) rather than using a single thick uniform layer. This segmentation allows the structure to suppress leakage current while maintaining light transmission by creating potential barriers only for carriers, not for photons.
Solution Approach 2:
The buffer layer uses a composite structure combining InP and AlGaInAs materials with different bandgap energies. The AlGaInAs layers have wider bandgaps that create potential barriers for carrier diffusion while being transparent to the optical communication wavelength, achieving both leakage suppression and sensitivity preservation.
2Reliability
If a thick buffer layer is grown to prevent mutual diffusion between Fe and Zn, then device yield improves, but productivity decreases due to extended growth time and material consumption
Solution Approach 1:
The buffer layer is divided into multiple thin alternating layers of InP and AlGaInAs, each with optimized thickness. This segmented structure achieves effective diffusion barrier functionality with much reduced total thickness compared to a conventional thick uniform buffer layer, thereby reducing growth time and material consumption while maintaining yield.
Solution Approach 2:
The buffer layer structure changes the composition parameter by introducing AlGaInAs layers with different material properties than pure InP. This parameter change enables the buffer to achieve diffusion barrier functionality at reduced thickness, improving productivity while maintaining device yield.
3Productivity
If multiple diodes are formed side by side on the substrate, then optical communication capacity increases, but leakage current increases due to insufficient separation between diodes
Solution Approach 1:
The buffer layer is segmented into multiple thin alternating layers that create lateral potential barriers between adjacent diodes. This segmentation enables sufficient electrical isolation between closely spaced diodes, allowing high-density integration for increased communication capacity while suppressing inter-diode leakage current.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The superlattice buffer layer effectively reduces leakage current and maintains light-receiving sensitivity by acting as a barrier to electrons and not absorbing incident light, thereby improving device yield and productivity while preventing light absorption.
Implementation Method 1
an undoped InP layer may be made to grow into a thick buffer layer on an Fe-doped semi-insulating InP substrate to thereby separate the substrate from the p-type contact layer
Implementation Method 2
incident light may be absorbed in the buffer layer, causing light-receiving sensitivity to deteriorate
Data Source
AI summary
A semiconductor light-receiving device includes: a semi-insulating substrate; and a buffer layer, a p-type contact layer, a light absorption layer, a p-type field alleviating layer, an avalanche multiplication layer, an n-type field alleviating layer and an n-type contact layer laminated in order on the semi-insulating substrate, wherein the buffer layer includes a superlattice obtained by alternately laminating an InP layer and an AlxGayIn1-x-yAs layer (0.16≤x≤0.48, 0≤y≤0.31) and does not absorb light of a wavelength band absorbed by the light absorption layer.