Mesa APD with Thinner Edge Avalanche Layer
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Solution Overview
Problem
Mesa structure avalanche photodiodes (APDs) experience edge breakdown issues due to higher electric field intensity at the side faces, leading to reduced breakdown voltage and excessive noise, which impairs their high-speed and low-noise performance in optical communication systems.
Innovation Solution
The semiconductor photodetector design incorporates a mesa structure with a thinner avalanche multiplication layer at the side faces compared to the central portion, and a lower carrier concentration or impurity concentration at the side faces, preventing edge breakdown by increasing the breakdown voltage and ensuring uniform electric field distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a mesa structure is used to reduce capacitance for high-speed operation, then the response speed is improved, but edge breakdown occurs due to higher electric field intensity at the side faces
Solution Approach 1:
The patent applies local quality by creating different avalanche multiplication layer thicknesses at different locations within the mesa structure. The central region has a thicker avalanche multiplication layer for high multiplication gain, while the peripheral region has a thinner layer to reduce electric field intensity and prevent edge breakdown. This spatial variation in layer thickness allows simultaneous optimization of both response speed and edge breakdown resistance.
2Reliability
If the avalanche multiplication layer thickness is increased to achieve higher multiplication factor, then the sensitivity is improved, but the breakdown voltage decreases due to higher electric field intensity
Solution Approach 1:
The patent implements local quality by varying the avalanche multiplication layer thickness across the device area. The central photodetective portion has sufficient thickness to achieve high multiplication factors and sensitivity, while the peripheral portions have reduced thickness to maintain higher breakdown voltages. This resolves the contradiction between sensitivity and breakdown voltage by optimizing each region's thickness for its specific function.
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 enhances the reliability and sensitivity of the photodetector by preventing edge breakdown, allowing for higher multiplication factors and reduced noise, thereby supporting high-speed and low-noise operation in optical communication systems.
Implementation Method 1
an avalanche multiplication layer for causing avalanche multiplication to occur
Implementation Method 2
a light absorbing layer for absorbing light incident from the backside of a semiconductor substrate and converting it into an electric signal
Data Source
AI summary
In order to improve reliability by preventing an edge breakdown in a semiconductor photodetector having a mesa structure such as a mesa APD, the semiconductor photodetector includes a mesa structure formed on a first semiconductor layer of the first conduction type formed on a semiconductor substrate, the mesa structure including a light absorbing layer for absorbing light, an electric field buffer layer for dropping an electric field intensity, an avalanche multiplication layer for causing avalanche multiplication to occur, and a second semiconductor layer of the second conduction type, wherein the thickness of the avalanche multiplication layer at the portion in the vicinity of the side face of the mesa structure is made thinner than the thickness at the central portion of the mesa structure.