SWIR Photodetector Buffer Structure for Lower Dark Current
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Solution Overview
Problem
Conventional photodetectors for detecting Short-Wave Infrared (SWIR) light suffer from high dark current due to significant lattice mismatch between the substrate and absorber layers, leading to compressive strain and dislocation density, which limits their performance and cutoff wavelength.
Innovation Solution
A photodetector design using an indium arsenide (InAs) substrate with a set of reverse-graded buffer layers and an absorber layer having a smaller lattice constant, such as indium gallium arsenide (InxGa1-xAs), indium arsenide phosphide (InAsxP1-x), or indium aluminum arsenide (InxAl1-xAs), which reduces lattice mismatch and strain, resulting in lower dislocation density and dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional photodetector design with standard substrate and absorber layers is used, then manufacturing is simpler, but dark current is high due to lattice mismatch
Solution Approach 1:
The buffer layer is segmented into multiple sub-layers with progressively varying composition and lattice constants. Each sub-layer acts as an intermediate transition zone, gradually adapting the lattice constant from the substrate to the absorber layer, thereby reducing dislocation density and dark current while maintaining manageable manufacturing complexity
Solution Approach 2:
The lattice constant of the buffer layers is systematically changed by varying the composition ratio of InAs and InP in each sub-layer. This parameter change creates a gradient structure that reduces lattice mismatch between the InAs substrate and InAs1-xSbx absorber layer, effectively lowering dark current without requiring completely new materials or processes
2Length of stationary object
If absorber layer with smaller lattice constant is used, then cutoff wavelength increases, but lattice mismatch with substrate increases causing more dislocations
Solution Approach 1:
The gradient buffer layers act as intermediary structures between the InAs substrate and the InAs1-xSbx absorber layer with smaller lattice constant. These buffer layers with intermediate lattice constants serve as transition zones that accommodate the lattice mismatch, allowing the use of absorber materials with smaller lattice constants (for longer cutoff wavelengths) without generating excessive dislocations
Solution Approach 2:
Different regions of the buffer layer structure have different local compositions and lattice constants tailored to their specific positions. The buffer layers closer to the substrate have compositions intermediate between substrate and absorber, while those closer to the absorber have compositions closer to the absorber material, creating locally optimized transitions that reduce dislocation density throughout the structure
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
The design achieves improved performance with reduced dark current and higher cutoff wavelength, enabling effective detection of SWIR light while providing design flexibility for the bandgap of the absorber layer.
Implementation Method 1
significant lattice mismatch between the substrate and absorber layers, leading to compressive strain and dislocation density
Implementation Method 2
detecting Short-Wave Infrared (SWIR) light
Data Source
AI summary
A photodetector may include a substrate having a larger lattice constant than an absorber layer. A reverse graded set of buffer layers may provide lattice matching between the substrate and the absorber layer. The substrate may comprise indium arsenide (InAs). The absorber layer may comprise one of indium gallium arsenide (InxGa1-xAs), indium arsenide phosphide (InAsxP1-x), and indium aluminum arsenide (InxAl1-xAs).