Indirect Band Gap Contact Layer for High-Bandwidth Photodiodes
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Solution Overview
Problem
Existing photodiodes based on III-V semiconductor materials, such as InAlAs, are inefficient in detecting lower wavelengths due to high absorption in the contact layer, which limits their speed and bandwidth.
Innovation Solution
A surface-illuminated photodiode with a substrate made of InP and a doped contact layer composed of semiconductor material with an indirect band gap, reducing absorption of lower wavelengths by allowing light to be transmitted through the contact layer into the absorption layer, thereby enhancing carrier transport and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a contact layer with large thickness is used to achieve low resistance contact, then contact resistance is reduced, but light absorption in the contact layer increases
Solution Approach 1:
The patent changes the fundamental optical parameter of the contact layer by selecting a material with indirect band gap (AlGaAsSb, InAlAsSb, or AlAsSb) instead of conventional direct band gap materials. This material parameter change enables the contact layer to become transparent to specific wavelength ranges while maintaining electrical functionality, thus resolving the contradiction between low resistance contact and minimal light absorption.
Solution Approach 2:
The patent employs composite material structures where the contact layer is formed from specific semiconductor compositions (AlGaAsSb, InAlAsSb, or AlAsSb) that combine the properties of low electrical resistance with optical transparency. These composite materials allow simultaneous optimization of both electrical and optical performance in the contact layer.
2Reliability
If a contact layer material with direct band gap is used, then low resistance contact is achieved, but absorption of lower wavelengths occurs
Solution Approach 1:
The patent fundamentally changes the optical parameter of the contact layer by using materials with indirect band gap structures. This parameter change shifts the material's optical response, creating transparency windows at specific wavelengths while maintaining electrical conductivity, thereby eliminating the harmful absorption effect at lower wavelengths.
Solution Approach 2:
The patent applies the local quality principle by making the contact layer selectively transparent to certain wavelengths while maintaining its electrical function. The indirect band gap materials provide different optical properties at different wavelength ranges, allowing the same layer to serve both electrical contact and optical transparency functions locally.
3Reliability
If contact layer thickness is increased to reduce contact resistance, then electrical performance improves, but carrier transport speed decreases
Solution Approach 1:
By changing the material parameter from direct to indirect band gap, the patent enables the contact layer to simultaneously provide low resistance contact and fast carrier transport. The indirect band gap materials reduce unwanted light absorption and minimize carrier generation in the contact layer, allowing faster carrier transport while maintaining electrical performance.
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 use of an indirect band gap contact layer reduces absorption of lower wavelengths, resulting in faster carrier transport and higher bandwidth, making the photodiode suitable for high-speed applications in optical communication systems.
Implementation Method 1
the contact layer comprises or consists of a semiconductor material having an indirect band gap and has a thickness of at least 200 nm. Using a semiconductor material with an indirect band gap as the (e.g. top) contact layer reduces or eliminates absorption of light having a wavelength e.g. lower than 840 nm.
Implementation Method 2
the absorption layer is to be illuminated through the contact layer... the generation of electron-hole pairs in the contact layer is reduced or eliminated resulting, in turn, in a faster carrier transport and thus in a higher bandwidth of the photodiode.
Data Source
AI summary
Provided is a photodiode, including a substrate formed by a III-V semiconductor material. The substrate is made of InP; at least one light absorption layer; and at least one doped contact layer. The absorption layer is to be illuminated through the contact layer. The contact layer includes a semiconductor material having an indirect band gap and has a thickness of at least 200 nm.