Ge-on-Si Time-of-Flight Sensor Structure for Low Dark Current
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Solution Overview
Problem
Indirect time of flight (iTOF) sensors using Si as a detector material are inefficient for infrared light due to low light absorption, and Ge-based sensors have higher dark current issues due to a smaller bandgap and high density of states, limiting their performance.
Innovation Solution
A time of flight sensor design featuring a Si-based photocurrent collecting structure with an n-doped and p-doped region, where the Ge-based photosensitive structure is epitaxially grown, allowing for efficient photocurrent conduction and reduced dark current through barrier configurations and doping gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Ge-based photosensitive structure is used to improve infrared light absorption, then sensitivity to infrared light is improved, but dark current increases due to smaller bandgap and higher density of states
Solution Approach 1:
The sensor is segmented into distinct functional regions: a Ge-based photosensitive structure for infrared detection and a Si-based photocurrent collecting structure for carrier collection. This segmentation allows each material to perform its optimal function while mitigating Ge's dark current issue by separating the photosensitive function from the collection function.
Solution Approach 2:
The Si-based photocurrent collecting structure acts as an intermediary between the Ge photosensitive structure and the external circuit. It collects photocurrents generated in the Ge layer while being insensitive to infrared light itself, thus preventing dark current generation in the collection path and enabling efficient carrier extraction.
2Object-generated harmful factors
If Si-based detector material is used, then dark current is reduced due to larger bandgap, but light absorption efficiency decreases for infrared wavelengths
Solution Approach 1:
Different regions of the sensor are assigned different material qualities optimized for their specific functions: Ge material with high infrared absorption coefficient is used locally in the photosensitive layer where light detection is needed, while Si material with low dark current is used in the photocurrent collecting structure where carrier collection occurs.
Solution Approach 2:
The sensor employs a composite structure combining Ge and Si materials in a vertically integrated architecture. The Ge-based photosensitive structure provides superior infrared absorption, while the Si-based photocurrent collecting structure provides low-dark-current carrier collection, creating a composite system that leverages the advantages of both materials.
3Productivity
If n-doped and p-doped regions are introduced to improve photocurrent conduction, then carrier collection efficiency is improved, but device complexity increases
Solution Approach 1:
The n-doped and p-doped regions are merged into a single integrated Si-based photocurrent collecting structure that simultaneously performs both electron collection (via n-doped region) and hole collection (via p-doped region). This unified structure collects both types of carriers generated in the Ge photosensitive layer through a single architectural element, reducing overall device complexity.
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 enhances the sensitivity and efficiency of time of flight sensors to infrared light, reducing material consumption and energy use, contributing to green technology solutions by minimizing dark current and ohmic losses.
Implementation Method 1
Sensor pixels, wherein a Ge-based photosensitive structure is epitaxially grown on a Si-based photocurrent collecting structure
Implementation Method 2
the photocurrent collecting structure comprises 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
Implementation Method 3
wherein the conduction band in the p-doped region comprises a barrier for the electrons of the photocurrent and the valence band in the n-doped region comprises a barrier for the holes of the photocurrent
Data Source
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AI summary
A time of flight sensor comprises at least one pixel, comprising: a Si-based photocurrent collecting structure (110) and a Ge-based photosensitive structure (120) epitaxially grown on the photocurrent collecting structure, wherein the photocurrent collecting structure comprises an n-doped region (111) and a p-doped region (112), wherein the n-doped region is configured to conduct electrons of a photocurrent to at least one n-contact (130) and wherein the p-doped region is configured to conduct holes of the photocurrent to at least one p-contact (140) and wherein the conduction band in the p-doped region comprises a barrier for the electrons of the photocurrent and the valence band in the n-doped region comprises a barrier for the holes of the photocurrent.