Mesa Photodetectors With Lateral Diffusion Junctions
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Solution Overview
Problem
Mesa-type PIN photodiodes face reliability issues due to exposure of sensitive narrow-bandgap absorption layers, which current passivation methods, such as dielectric coatings and epitaxial regrowth, fail to adequately address, especially in high-speed applications requiring low dark current and stringent aging test performance.
Innovation Solution
A simple Zn diffusion process is used to create a diffused p-n junction interface at the etched mesa trench, converting epitaxial material into a different dopant type, providing superior reliability without adding complexity or cost, and combining with surface passivation techniques like polyimide or SiN for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If mesa-type structure is used to reduce capacitance and increase bandwidth, then speed and bandwidth are improved, but reliability deteriorates due to exposure of narrow-bandgap absorption layer to foreign material
Solution Approach 1:
The patent applies local quality by implementing a guard ring structure specifically at the peripheral regions where the narrow-bandgap absorption layer is exposed, while leaving the central active region unchanged. This localized approach provides targeted protection against foreign material contamination at the vulnerable edges without affecting the optical performance of the main device area, thus resolving the contradiction between maintaining high bandwidth and improving reliability.
2Reliability
If passivation coating is applied to seal mesa walls, then reliability is improved, but dark current increases and performance becomes inconsistent
Solution Approach 1:
The patent extracts or removes the problematic passivation coating approach and replaces it with a guard ring structure that provides protection through a different mechanism. The guard ring creates a lateral diffusion barrier that prevents foreign material from reaching the absorption layer without introducing the harmful effects of dielectric coatings, such as increased dark current and inconsistent performance, thus resolving the contradiction between reliability improvement and harmful side effects.
3Manufacturing precision
If epitaxial regrowth or dielectric coating is used for passivation, then surface defects are reduced, but manufacturing complexity and cost increase
Solution Approach 1:
The patent employs a simpler, more economical guard ring structure that can be implemented using standard semiconductor fabrication processes without requiring complex epitaxial regrowth equipment or multiple dielectric deposition steps. This approach achieves surface defect reduction through lateral diffusion barrier formation, which is a more straightforward and cost-effective process compared to the alternative passivation methods, thus resolving the contradiction between manufacturing precision and 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 approach results in a mesa-type PIN photodiode with improved reliability, meeting data-com and telecom requirements by effectively terminating the absorption layers and reducing dark current, while maintaining lower parasitic capacitance and higher bandwidth.
Implementation Method 1
A simple Zn diffusion process is used to create a diffused p-n junction interface at the etched mesa trench, converting epitaxial material into a different dopant type
Data Source
AI summary
The present invention relates to a stable mesa-type photodetector with lateral diffusion junctions. The invention has found that without resorting to the complicated regrowth approach, a simple Zn diffusion process can be used to create high-quality semiconductor junction interfaces at the exposed critical surface or to terminate the narrow-bandgap photon absorption layers. The invention converts the epi material layers near or at the vicinity of the etched mesa trench or etched mesa steps into a different dopant type through impurity diffusion process. Preferably the diffused surfaces are treated with a subsequent surface passivation. This invention can be applied to both top-illuminating and bottom-illuminating configurations.