CdHgTe Multispectral Photodiode Array via Cadmium Diffusion
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Solution Overview
Problem
Existing CdHgTe infrared photodiode matrices face challenges such as limited multi-spectral detection capabilities, high dark current, noise levels due to etching defects, and the need for complex molecular beam epitaxy growth techniques, which restrict their efficiency and scalability.
Innovation Solution
A method involving the deposition of cadmium-rich material on a CdHgTe semiconductor layer, followed by inter-diffusion annealing to create pixels with varying cadmium concentrations, eliminating the need for etching and allowing for multi-spectral detection without the limitations of bi-spectral detection, reduced noise, and compatibility with liquid phase epitaxy growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If molecular beam epitaxy (EJM) is used to grow high quality crystalline layers of variable composition, then the manufacturing precision and quality of photodiode layers are improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent changes the growth method parameter from molecular beam epitaxy to liquid phase epitaxy, and introduces cadmium concentration as a controllable parameter to achieve spectral differentiation. This allows obtaining variable composition layers with good quality through a simpler process
Solution Approach 2:
Instead of using complex EJM to create each layer, the patent uses a simpler EPL process that replicates the essential functionality of creating high-quality crystalline layers with controlled composition, achieving similar results through a less complex method
2Adaptability or versatility
If trenches are etched to uncover the lower layer and produce PN junctions, then the multi-spectral detection capability is improved, but the dark current and noise level increase due to etching defects
Solution Approach 1:
The patent performs preliminary action by creating the cadmium concentration gradient within the single layer before forming the PN junctions. This eliminates the need for subsequent trench etching to access different composition regions, thereby avoiding etching-induced defects while preserving multi-spectral detection capability
Solution Approach 2:
The patent segments the single crystalline layer into multiple functional regions with different cadmium concentrations, creating spatially differentiated detection zones within one continuous layer, which avoids the need for physical separation via trench etching
3Adaptability or versatility
If doublets of two photodiodes are mounted head to tail separated by a barrier layer, then the bi-spectral detection is achieved, but the temporal coherence of detection is lost
Solution Approach 1:
The patent merges multiple spectral detection capabilities into a single integrated photodiode structure by creating a cadmium concentration gradient within one continuous layer. This allows all spectral channels to be detected simultaneously from different regions of the same layer, maintaining temporal coherence while achieving multi-spectral detection
Solution Approach 2:
The single photodiode layer is designed to perform multiple spectral detection functions simultaneously through spatially varying cadmium concentration, making one structure universal for detecting multiple wavelengths rather than requiring separate dedicated photodiodes for each spectral band
4Measurement precision
If multiple growths of high quality crystalline layers with variable composition are performed, then the multi-spectral detection precision is improved, but the productivity decreases
Solution Approach 1:
The patent segments the spectral detection function across different regions of a single layer with varying cadmium concentration, eliminating the need for multiple separate layer growths. This maintains spectral precision while significantly improving manufacturing efficiency by reducing the number of growth cycles required
Solution Approach 2:
The patent uses cadmium concentration as a controllable parameter during a single growth process to create regions with different spectral responses. This allows obtaining multiple spectral channels from one growth run rather than requiring multiple growths, thereby improving productivity while maintaining detection precision
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 approach enables the production of multi-spectral photodiode arrays with reduced dark current and noise, improved electro-optical performance, and simplified manufacturing, allowing for time-coherent multi-spectral detection and cost-effective production.
Implementation Method 1
inter-diffusion annealing, carrying out the diffusion of the cadmium atoms from the cadmium-rich material towards the semiconductor layer
Implementation Method 2
inter-diffusion annealing
Data Source
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AI summary
The invention relates to a method for fabricating a multispectral photodiode array in a CdxHg1-xTe semiconductor layer (120) composed of pixels (121), the method comprising a step of creating a PN junction (141) in each pixel. The method according to the invention comprises the following steps: - fabrication (101) of a cadmium-rich structure (170) on the semiconductor layer, structured such that not all pixels (121) are topped with the same quantity of cadmium atoms, this quantity being possible to be zero; and - inter-diffusion annealing (102), carrying out the diffusion of cadmium atoms from the cadmium-rich structure (170) to the semiconductor layer (120). This results in pixels (121) that do not all have the same cutoff wavelength.