SiC Avalanche Photodiode Edge Termination for Uniform Breakdown
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Solution Overview
Problem
Avalanche photodiodes (APDs) face challenges with breakdown voltage non-uniformity and high dark current rates due to disparate breakdown voltages in arrays, leading to increased false detection events and complex circuitry requirements, especially in Geiger mode operation, where high gain levels are necessary for single photon detection.
Innovation Solution
The APD design incorporates a structure with a base n+ doped material layer, an n− doped layer for photon absorption, and a p+ doped layer, along with non-planar floating guard rings and angled sidewalls to achieve uniform breakdown voltage and reduce dark current, utilizing epitaxial growth over n+ SiC substrates for low defect density and pure hole-initiated impact ionization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SiC APDs are operated at high gain levels for single photon detection in Geiger mode, then detection sensitivity is improved, but premature edge breakdown occurs leading to increased dark current
Solution Approach 1:
The patent applies different doping concentrations at different locations: heavy n+ doping at the edges and lighter n- doping in the center. This local quality variation creates a non-uniform doping profile that suppresses edge breakdown while maintaining bulk performance, directly resolving the contradiction between high gain operation and dark current suppression
Solution Approach 2:
The patent changes the doping concentration parameter spatially, creating a graded doping profile where the doping concentration varies from the center to the edges. This parameter change allows the device to achieve both high gain capability and low dark current by optimizing the electric field distribution through controlled doping variations
2Adaptability or versatility
If APDs with disparate breakdown voltages are included in the same array, then array coverage is improved, but breakdown voltage non-uniformity increases leading to higher dark count rates
Solution Approach 1:
The patent achieves homogeneous breakdown voltage characteristics across all APDs in the array through the non-uniform doping profile. By controlling the edge termination with heavy n+ doping, the patent ensures uniform electric field distribution at the edges, which standardizes the breakdown voltage across different devices, enabling reliable array operation with flexible composition
3Reliability
If breakdown voltage uniformity is maintained for low dark count rates, then detection accuracy is improved, but complex circuitry is required to bias each APD individually
Solution Approach 1:
The patent changes the doping concentration parameter to create a non-uniform doping profile with heavy n+ doping at edges and lighter n- doping in the center. This parameter variation inherently provides breakdown voltage uniformity across the array, eliminating the need for complex individual biasing circuitry while maintaining low dark count rates
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 ensures low excess noise, low dark current, and uniform breakdown voltage, allowing for high gain operation without premature edge breakdown, reducing dark count rates and enabling simplified biasing circuitry for APD arrays, while maintaining low excess noise and high reliability for Geiger mode operation.
Implementation Method 1
an n− doped material layer (30) formed on the n+ doped material layer (52), with the n− doped material layer (30) having a portion of a lower surface (74) exposed for receiving the photon (22) impinging on the avalanche photodiode device (20)
Implementation Method 2
Photogenerated carriers in the depletion region of the p-n junction travel at their saturated velocities, and if they acquire enough energy from the field during such transit, an ionizing collision with the lattice can occur. In the process, secondary electron-hole pairs are produced
Implementation Method 3
Avalanche photodiodes (APDs) are essentially reverse-biased p-n junctions that are operated at voltages close to the breakdown voltage
Data Source
AI summary
An avalanche photodiode semiconductor device (20) for converting an impinging photon (22) includes a base n+ doped material layer (52) formed having a window section (72) for passing the photon (22). An n− doped material layer (30) is formed on the n+ doped material layer (52) having a portion of a lower surface (74) suitably exposed. An n+ doped material layer (32) is formed on the n− doped material (30). A p+ layer (24) formed on top of the n+ doped layer (32). At least one guard ring (26) is formed in the n− doped layer (30).