Stacked Germanium Photodetector Contact Layout for Low Dark Current
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Solution Overview
Problem
Photodetectors with germanium as a light absorption material suffer from defects due to lattice mismatch when epitaxially grown on silicon, leading to increased dark current, noise, and decreased photosensitivity.
Innovation Solution
A stacked photodetector design is implemented with at least one contact region on the germanium sensing region instead of adjacent to it, reducing the surface area interfaced with the substrate and minimizing lattice mismatch, thereby reducing misfit defects and dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If germanium is epitaxially grown on silicon substrate, then photosensitivity is improved, but lattice mismatch causes misfit defects and increased dark current
Solution Approach 1:
The patent segments the contact structure into multiple components: a first contact adjacent to the germanium sensing region, a second contact on the sensing region, and an extended region connecting them. This segmentation allows the electric field to be distributed and controlled, enabling effective charge collection while minimizing the interface area between germanium and silicon substrate, thereby reducing misfit defects and dark current generation
Solution Approach 2:
The patent extends the contact structure into a third dimension by creating an extended region that protrudes from the substrate surface. This dimensional extension allows the contact to reach the germanium sensing region without requiring a large interface area on the substrate, thus maintaining effective electrical connection while minimizing lattice mismatch effects
2Ease of manufacture
If contact region is placed adjacent to germanium sensing region, then manufacturing is simplified, but surface area interfaced with substrate increases causing more misfit defects
Solution Approach 1:
The extended region acts as an intermediary structure that connects the first contact (adjacent to sensing region) and the second contact (on sensing region). This intermediary allows the contact system to achieve both manufacturing simplicity and low defect density by providing a controlled path for charge collection that minimizes the germanium-silicon interface area
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 dark current by 30% to 40%, enhancing photosensitivity, low-light performance, and image quality by minimizing noise and defects.
Implementation Method 1
A photodetector is a semiconductor device that is configured to receive photons of incident light and convert the photons to an electrical signal. The photons generate electron/hole pairs in a light absorption material of the photodetector.
Data Source
AI summary
A stacked (or vertically arranged) photodetector having at least one contact region on a germanium sensing region. Including the at least one contact on the germanium sensing region reduces the amount of surface area of the germanium sensing region that is interfaced with a substrate (e.g., a silicon substrate) in which the germanium sensing region is included. This reduces the amount of lattice mismatch reduces the amount of misfit defects for the germanium sensing region, which reduces the dark current for the photodetector. The reduced amount of dark current may increase the photosensitivity of the photodetector, may increase low-light performance of the photodetector, and/or may decrease noise and other defects in images and/or light captured by the photodetector, among other examples.