Ge-on-Si Time-of-Flight Pixel With Carrier Barriers for Low Dark Current
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Solution Overview
Problem
Indirect time-of-flight (iTOF) sensors using Si as a detector material for infrared light around 900 nm suffer from low light absorption and high dark current due to Ge's smaller bandgap and high density of states, which can be addressed by incorporating a Ge-based photosensitive structure epitaxially grown on a Si-based photocurrent collecting structure with specific doping configurations.
Innovation Solution
A time-of-flight sensor design featuring a Si-based photocurrent collecting structure with n-doped and p-doped regions, where the p-doped region includes a barrier for electrons and the n-doped region includes a barrier for holes, combined with a Ge-based photosensitive structure, which is epitaxially grown on the photocurrent collecting structure, and optionally includes a charge sheet to reduce electric field strength and a doping gradient to enhance charge separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If Ge-based photosensitive structure is used to improve infrared sensitivity, then light absorption is improved, but dark current increases
Solution Approach 1:
The sensor is divided into two distinct functional regions: a Si-based photocurrent collecting structure and a Ge-based photosensitive structure. This segmentation allows each material to perform its optimal function - Si for low dark current and Ge for high infrared absorption - thereby resolving the contradiction between sensitivity and dark current
Solution Approach 2:
The patent employs a composite structure combining Si and Ge materials with different bandgap properties. The Si-based structure provides low dark current characteristics while the Ge-based layer enhances infrared absorption, creating a composite material system that achieves both improved sensitivity and controlled dark current
2Reliability
If p-doped region barrier for electrons is implemented, then charge carrier separation is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by implementing specific doping types in specific regions: p-doping in regions where electron barriers are needed and n-doping where hole barriers are needed. This localized doping strategy achieves effective charge carrier separation while maintaining manufacturing feasibility through standard semiconductor processing techniques
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
This design reduces material consumption, ohmic losses, and chemical waste, enabling energy and resource savings while improving sensor performance by minimizing dark current and enhancing charge carrier separation.
Implementation Method 1
Indirect time-of-flight (iTOF) sensors may use infrared light, for example infrared light with a wavelength of about 900 nm
Implementation Method 2
the conduction band in the p-doped region includes a barrier for the electrons of the photocurrent and the valence band in the n-doped region includes a barrier for the holes of the photocurrent
Implementation Method 3
a Ge-based photosensitive structure epitaxially grown on the photocurrent collecting structure
Data Source
AI summary
A time-of-flight sensor includes at least one pixel, including: a Si-based photocurrent collecting structure and a Ge-based photosensitive structure epitaxially grown on the photocurrent collecting structure, wherein the photocurrent collecting structure includes an n-doped region and a p-doped region, wherein the n-doped region is configured to conduct electrons of a photocurrent to at least one n-contact and wherein the p-doped region is configured to conduct holes of the photocurrent to at least one p-contact and wherein the conduction band in the p-doped region includes a barrier for the electrons of the photocurrent and the valence band in the n-doped region includes a barrier for the holes of the photocurrent.