Light Detector Gradient Layer for Lattice Mismatch Control
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Solution Overview
Problem
Conventional semiconductor light detecting devices experience lattice mismatch and stress due to differences in lattice constants between layers, leading to defects and increased dark current, which can affect accuracy and usability.
Innovation Solution
A light detecting device is designed with a substrate, a buffer layer, a gradient layer with sublayers of increasing lattice constants, and a barrier layer with a predetermined lattice constant greater than the substrate, to alleviate lattice mismatch stress and reduce defects, featuring a gradual change in lattice constants from the substrate to the barrier layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a buffer layer is disposed between the substrate and the quantum well layer to handle lattice mismatch, then the interface between substrate and quantum well layer is improved, but stress accumulates continually during epitaxy due to great difference in lattice constants
Solution Approach 1:
The buffer layer is segmented into multiple sublayers with gradually changing compositions. Each sublayer has a slightly different lattice constant, creating a gradient that transitions from the substrate lattice constant to the quantum well layer lattice constant. This segmentation distributes the lattice mismatch across multiple interfaces rather than one abrupt interface, reducing stress accumulation in each individual interface while maintaining overall interface quality.
Solution Approach 2:
The lattice constant parameter is changed gradually across the buffer layer thickness by varying the material composition in each sublayer. This creates a lattice constant gradient that smoothly transitions between the substrate and quantum well layer values, allowing stress to be distributed and released progressively rather than accumulated at a single interface.
2Stress or pressure
If the lattice constants of layers are made substantially the same to avoid mismatch, then stress accumulation is reduced, but the buffer layer cannot serve as an effective buffer when quantum well layer compositions are quite different from substrate
Solution Approach 1:
Different sublayers within the buffer layer have different local compositions tailored to their specific position. Sublayers closer to the substrate have compositions closer to the substrate lattice constant, while sublayers closer to the quantum well layer have compositions closer to the quantum well layer lattice constant. This local quality variation allows each sublayer to effectively buffer the specific lattice mismatch at its location while collectively providing comprehensive buffering across the entire interface region.
Solution Approach 2:
The material composition parameter is systematically changed across the buffer layer thickness to create a gradient structure. This parameter change enables the buffer layer to adapt to different lattice constants at different positions, providing effective buffering capability for quantum well layers with compositions quite different from the substrate while maintaining low stress accumulation through the gradual transition.
3Productivity
If epitaxy growth is performed with large lattice constant differences, then device functionality is achieved, but defects of various magnitude appear in each layer affecting performance
Solution Approach 1:
The buffer layer is divided into multiple sublayers that segment the large lattice constant difference into smaller incremental steps. This segmentation prevents the formation of large-magnitude defects by ensuring that each interface between adjacent sublayers has only a small lattice constant difference, thereby maintaining high manufacturing precision while enabling device functionality through controlled epitaxy growth.
Solution Approach 2:
The lattice constant parameter is changed gradually through the buffer layer thickness by controlling material composition in each sublayer. This controlled parameter change during epitaxy growth prevents abrupt lattice transitions that cause defects, allowing device functionality to be achieved with minimal defect density in each layer.
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 solution effectively reduces defects and dark current, improving the accuracy and reliability of the light detecting device by minimizing stress during epitaxy growth and ensuring better product quality.
Implementation Method 1
due to difference between lattice constants of the layers in the light detecting device 1 being too great, despite having the buffer layer 12 disposed between the substrate 11 and the quantum well layer 13, lattice mismatch still occurs often and thereby stress in the layers is accumulated continually during epitaxy
Implementation Method 2
the light enters from the opening and shines on the absorption layer 14, which absorbs energy from the light and transmits the light energy to the quantum well layer 13
Implementation Method 3
when the quantum well layer 13 absorbs the light and generates an energy shift, the electric signals that correspond to the light absorbed by the absorption layer 14 are generated
Data Source
AI summary
A light detecting device includes a substrate that has a lattice constant. A buffer layer is disposed on the substrate. A gradient layer is formed on the buffer layer opposite to the substrate, and includes a plurality of sublayers that have respectively lattice constants each of which is greater than the lattice constant of the substrate. The sublayers are arranged in a manner that the lattice constants of the sublayers undergo a gradual increase in lattice constant in a direction away from the substrate. A barrier layer is formed on the gradient layer opposite to the buffer layer, and has a lattice constant which is greater than that of the substrate and no smaller than the lattice constants of the sublayers. An absorption layer is formed on the barrier layer opposite to the gradient layer.