Semiconductor Photodetector Leakage Reduction via Surface Segmentation
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Solution Overview
Problem
Semiconductor photodetectors, particularly those made of germanium, suffer from high leakage currents that hinder their sensitivity, especially for infrared light detection, as they are not effectively suppressed by existing methods, leading to high dark current densities that compete with photocurrent, making them unsuitable for indoor or twilight imaging applications.
Innovation Solution
A low-noise photodetector design featuring a semiconductor body surrounded by dielectric material with a passivated and unpassivated surface, incorporating opposite polarity p-n junctions, highly doped regions, and charge accumulation layers to minimize leakage, where the p-n junction intersects the passivated surface and carriers must cross two junctions to reach the photocurrent collector, reducing surface leakage and diffusion current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a depletion layer intersects the semiconductor surface to enable photodetector operation, then the photodetector can detect light, but surface leakage current increases
Solution Approach 1:
The semiconductor body surface is divided into two distinct portions: a passivated portion where the p-n junction intersects to enable light detection, and an unpassivated portion that is heavily doped to suppress leakage. This segmentation allows each region to perform its specific function optimally without compromising the other.
Solution Approach 2:
Different regions of the semiconductor surface are given different properties: the passivated portion maintains low surface recombination velocity for efficient carrier collection, while the unpassivated portion is heavily doped to create a high concentration of majority carriers that suppress leakage current. Each region's quality is optimized for its specific role.
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 significantly reduces leakage currents, enhancing the signal-to-noise ratio and improving the sensitivity of photodetectors for both visible and infrared light detection, enabling effective imaging in low-light conditions.
Implementation Method 1
A first portion of the body surface is passivated... The p-n junction (including its depletion region) intersects the semiconductor surface within the passivated portion of the surface
Implementation Method 2
Semiconductor photodiodes are widely used for the detection of light, both visible and infrared. They exploit the internal photoelectric effect, where electron-hole pairs are generated in the semiconductor by photon absorption and contribute to electrical conduction inside the device
Implementation Method 3
the body includes a highly doped region in contact with the dielectric... leakage from the unpassivated surface is minimized
Implementation Method 4
a doped semiconductor outside a thin dielectric provides a charge accumulation region adjacent the interface
Implementation Method 5
the p-n junction (including its depletion region) intersects the semiconductor surface... carriers must cross two junctions to reach the photocurrent collector
Data Source
AI summary
A photodetector is formed from a body of semiconductor material substantially surrounded by dielectric surfaces. A passivation process is applied to at least one surface to reduce the rate of carrier generation and recombination on that surface. Photocurrent is read out from at least one electrical contact, which is formed on a doped region whose surface lies entirely on a passivated surface. Unwanted leakage current from un-passivated surfaces is reduced through one of the following methods. (a) The un-passivated surface is separated from the photo-collecting contact by at least two junctions (b) The un-passivated surface is doped to a very high level, at least equal to the conduction band or valence band density of states of the semiconductor (c) An accumulation or inversion layer is formed on the un-passivated surface by the application of an electric field. Electrical contacts are made to all doped regions, and bias is applied so that a reverse bias is maintained across all junctions.