Photodiode Pad and Spacer Structure for Quantum Efficiency
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Solution Overview
Problem
Semiconductor photodiodes with small dimensions or thin photon conversion layers suffer from low quantum efficiency, particularly in capturing infrared radiation, with current technologies achieving efficiencies of only 5 to 7%, and struggle to absorb reflected light effectively.
Innovation Solution
A photodiode design featuring a central pad made of a material with a different optical index surrounded by spacers, both transparent to the operating wavelength, with the pad's lateral dimensions smaller than the wavelength, and a protective layer with a lower index, enhancing diffraction and antireflection effects to increase photon absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the lateral dimensions of the photodiode are reduced to be very small (comparable to wavelength), then the device size is reduced, but the quantum efficiency decreases
Solution Approach 1:
The patent introduces a vertical dimension solution by placing a pad structure on the light-receiving surface. This pad, with lateral dimensions smaller than the wavelength and surrounded by spacers, creates optical path modifications in the vertical dimension that enhance photon absorption without increasing the lateral footprint of the photodiode, thus maintaining small device size while improving quantum efficiency
Solution Approach 2:
The patent modifies optical parameters by using materials with specific refractive indices. The pad material has index n1, spacer material has index n2, both smaller than the semiconductor index nSC, and the protection layer has index n3 smaller than both n1 and n2. This parameter optimization creates favorable optical conditions for enhancing photon absorption in small photodiodes
2Length of stationary object
If the conversion layer thickness is reduced to 1-1.5 μm, then the device complexity is reduced, but the photon conversion efficiency drops below 10%
Solution Approach 1:
Instead of increasing layer thickness vertically, the patent uses a surface-level pad structure with spacer elements that modify the optical field distribution. This approach enhances photon absorption probability in the existing thin conversion layer by creating favorable optical conditions at the surface, avoiding the need to increase layer thickness
Solution Approach 2:
The patent optimizes optical parameters through carefully selected material indices. The pad (n1), spacer (n2), and protection layer (n3) form a gradient structure with decreasing indices, creating optimal optical conditions that enhance photon absorption in the thin conversion layer without requiring thickness increase
3Reliability
If conventional antireflection structures are used, then some reflection is reduced, but the quantum efficiency gain is insufficient for small photodiodes
Solution Approach 1:
The pad structure surrounded by spacers serves multiple functions simultaneously: it acts as an antireflection element, creates diffraction effects to enhance light trapping, and modifies the optical field distribution. This multi-functional design achieves superior quantum efficiency improvement without proportionally increasing device complexity
Solution Approach 2:
The patent uses a composite structure consisting of pad material, spacer material, and protection layer material, each with specifically selected optical properties. This composite approach creates synergistic effects that enhance photon absorption more effectively than conventional single-material antireflection coatings
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 photon conversion into electron-hole pairs by 4 to 6% compared to traditional designs, significantly improving the detection of low-intensity light in small dimension photodiodes and thin conversion layer structures.
Implementation Method 1
enhancing diffraction and antireflection effects to increase photon absorption
Implementation Method 2
enhancing diffraction and antireflection effects to increase photon absorption
Implementation Method 3
semiconductor area 1 for converting photons into electron-hole pairs
Data Source
AI summary
A photodiode includes at least one central pad arranged on a light-receiving surface of a photodiode semiconductor substrate. The pad is made of a first material and includes lateral sidewalls surrounded by a spacer made of a second material having a different optical index than the first material. The lateral dimensions of the pad are smaller than an operating wavelength of the photodiode. Both the first and second materials are transparent to that operating wavelength. The pads and spacers are formed at a same time gate electrodes and sidewall spacers of MOS transistors are formed.