Germanium Photodiode Dark Current Reduction
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Solution Overview
Problem
Semiconductor-based photodiodes face challenges with high dark current and low absorption due to defects at heterogeneous interfaces and surface damage during etching processes, which degrade performance and increase leakage current.
Innovation Solution
The use of a germanium-based light absorption layer on a silicon substrate with a passivation layer and a spacer to reduce surface leakage current, combined with a counter doping layer and a conformal selective Ge etch process to minimize defects and enhance reflectivity, results in a photodiode with low leakage and high sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a germanium-based light absorption layer is used on a silicon substrate, then absorption efficiency is improved, but dark current increases due to defects at heterogeneous interfaces
Solution Approach 1:
An intrinsic or lightly-doped semiconductor layer is introduced between the germanium light absorption layer and the silicon substrate. This intermediate layer acts as a mediator that reduces defect formation at the heterogeneous interface, thereby lowering dark current while preserving the high absorption efficiency of germanium.
Solution Approach 2:
The patent applies different doping concentrations to different regions: the germanium layer maintains high absorption quality, the intermediate layer provides low-defect transition quality, and the substrate provides structural support. This local differentiation of material properties resolves the interface defect problem.
2Ease of manufacture
If etching processes are used to form photodiode structures, then device fabrication is enabled, but surface damage occurs increasing leakage current
Solution Approach 1:
Passivation layers are deposited on the semiconductor surfaces before etching processes to protect against surface damage. This preliminary protective action prevents the generation of leakage current-causing defects during subsequent fabrication steps.
Solution Approach 2:
The patent converts the potentially harmful etching process into a beneficial structure-forming step by using it to create precisely defined photodiode regions, while simultaneously applying passivation to neutralize the surface damage effects, thus transforming the harmful surface exposure into a controlled fabrication advantage.
3Device complexity
If the photodiode structure is simplified, then manufacturing complexity is reduced, but performance degradation occurs due to interface defects
Solution Approach 1:
The photodiode is segmented into distinct functional layers with different doping levels: high-doping regions for charge collection, an intrinsic or lightly-doped region for reducing interface defects, and a germanium layer for light absorption. This segmentation allows each layer to be optimized independently, maintaining high performance while enabling modular manufacturing.
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 approach leads to a photodiode with reduced dark current, improved absorption efficiency, and increased bandwidth, effectively addressing the limitations of existing semiconductor-based photodiodes by minimizing defects and surface damage.
Implementation Method 1
the photons can be absorbed in the intrinsic region and the generated photo-carriers can be collected from the P-type and N-type regions
Implementation Method 2
the surface leakage current can be reduced by passivating the first absorption layer
Implementation Method 3
a predetermined reflectivity can be achieved when an optical signal passing and being reflected by the sixth layer
Data Source
AI summary
A light absorption apparatus includes a substrate, a light absorption layer above the substrate on a first selected area, a silicon layer above the light absorption layer, a spacer surrounding at least part of the sidewall of the light absorption layer, an isolation layer surrounding at least part of the spacer, wherein the light absorption apparatus can achieve high bandwidth and low dark current.