Avalanche Photodiode Surface Structure to Reduce Optical Crosstalk
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Solution Overview
Problem
Photoelectric conversion apparatuses with avalanche photodiodes face issues of crosstalk due to photons being reflected from the silicon back surface of the moth-eye structure, leading to stray light and reduced image quality.
Innovation Solution
The apparatus incorporates a semiconductor layer with a plurality of avalanche diodes and uneven structures on the light-receiving surface, where the effective pitch of these structures is smaller than the wavelength of avalanche light emission, reducing reflection and stray light by allowing the light to travel further into the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a moth-eye structure is used in the photoelectric conversion element, then the optical path length is lengthened and quantum efficiency is improved, but photons are reflected from the silicon back surface causing crosstalk as stray light
Solution Approach 1:
The invention divides the light-receiving surface into multiple uneven structures (such as microlens arrays or tapered structures) that segment the incident light paths. This segmentation allows better control of light propagation, reducing back-surface reflections and crosstalk while maintaining enhanced quantum efficiency through extended optical paths.
Solution Approach 2:
The invention introduces three-dimensional uneven structures on the light-receiving surface, transitioning from a flat two-dimensional surface to a structured three-dimensional surface. This dimensional change creates multiple light-refracting interfaces that extend the optical path length and redirect photons away from the back surface, thereby reducing crosstalk while improving light absorption.
2Object-generated harmful factors
If the effective pitch of uneven structures is reduced below hc/Ea, then reflection and stray light are minimized, but manufacturing precision requirements increase
Solution Approach 1:
The invention optimizes the effective pitch parameter of the uneven structures to be smaller than hc/Ea (where h is Planck's constant, c is the speed of light, and Ea is the band gap energy). This parameter change effectively suppresses photon reflection and stray light generation. The specific pitch value can be adjusted based on the semiconductor material's band gap to achieve optimal performance.
Solution Approach 2:
The invention applies different local structures to different regions of the light-receiving surface, with each region's uneven structures optimized for its specific function. This local quality approach allows varying pitch and depth parameters in different areas to balance stray light reduction with manufacturing feasibility across the entire surface.
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 configuration effectively minimizes crosstalk and improves the quantum efficiency by ensuring that incident light is fully utilized, enhancing the overall performance of the photoelectric conversion system.
Implementation Method 1
Some photoelectric conversion apparatuses have an uneven structure in a light-receiving surface of a photoelectric conversion element to refract incident light, whereby the optical path length of the incident light in the photoelectric conversion element is lengthened
Implementation Method 2
a plurality of avalanche diodes disposed in a semiconductor layer
Implementation Method 3
each of the plurality of avalanche diodes including a first semiconductor region of a first conductivity type disposed at a first depth, and a second semiconductor region of a second conductivity type disposed at a second depth deeper than the first depth
Data Source
AI summary
A photoelectric conversion apparatus includes a plurality of avalanche diodes disposed in a semiconductor layer including a first surface and a second surface facing the first surface, and a first wiring structure in contact with the second surface, wherein a first pad configured to apply a first voltage to the photoelectric conversion apparatus is disposed in the first wiring structure, wherein the semiconductor layer includes a plurality of uneven structures disposed in the first surface, and wherein an effective pitch of the plurality of uneven structures is smaller than hc/Ea where h is a Planck constant [J·s], c is a speed of light [m/s], and Ea is a band gap [J] of a substrate.