CdHgTe Photodetector Cadmium Gradient for Low Dark Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing infrared photodiodes made of Cd x Hg 1-x Te face challenges in achieving sensitivity to long wavelengths while minimizing dark current, requiring precise control of cadmium concentration to avoid potential barriers that hinder minority carrier diffusion.
Innovation Solution
A photo-detection device with a semiconductor substrate of Cd x Hg 1-x Te, featuring a cadmium concentration gradient in the P-doped region, including an intermediate gap zone and a high gap zone, where the intermediate gap zone is in direct contact with the electrical contact pad, allowing for reduced dark current without compromising carrier collection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a box with high cadmium content is introduced into the P-doped region to reduce dark current, then dark current is reduced, but a potential barrier is formed that hinders minority carrier diffusion
Solution Approach 1:
The patent applies local quality by creating a non-uniform cadmium concentration distribution within the box structure. The cadmium concentration varies laterally across the box, with higher concentrations in specific regions and lower concentrations in other regions. This spatial variation in composition allows different zones of the box to serve different functions: high cadmium regions suppress dark current while low cadmium regions maintain carrier collection efficiency, thus resolving the contradiction between reducing dark current and maintaining reliability.
2Object-generated harmful factors
If cadmium concentration in the box is increased to reduce dark current, then dark current decreases, but sensitivity to long wavelengths is compromised
Solution Approach 1:
The patent implements local quality through a laterally non-uniform cadmium concentration profile in the box. Instead of using a uniform high cadmium concentration throughout the box, the concentration varies across different lateral regions. This allows the box to simultaneously achieve dark current suppression in high cadmium zones and wavelength sensitivity preservation in low cadmium zones, eliminating the need for precise control of a single uniform concentration value.
Solution Approach 2:
The patent applies parameter changes by varying the cadmium concentration parameter spatially within the box structure. The cadmium concentration is not fixed at a single value but changes across the lateral dimension of the box. This parameter variation enables the system to achieve both dark current reduction and sensitivity maintenance without requiring precise control of a single concentration parameter, as different regions operate with different concentration values.
3Reliability
If a shallow P-doped region is used to improve carrier collection, then carrier collection efficiency increases, but the ability to form an effective space charge zone is reduced
Solution Approach 1:
The patent applies local quality by creating spatial variation in cadmium concentration within the box that extends into the P-doped region. This non-uniform concentration profile allows the formation of an effective space charge zone through the cadmium gradient itself, rather than relying solely on the depth of the P-doped region. The local variations in composition create local electric field variations that facilitate both space charge zone formation and carrier collection in the shallow 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 cadmium concentration gradient enables increased sensitivity to long wavelengths while significantly reducing dark current, allowing for higher cadmium concentrations in the high gap zone and maintaining efficient carrier collection through the intermediate gap zone, thus improving the photodiode's performance.
Implementation Method 1
by carrying out an inter-diffusion anneal during which the cadmium atoms of the cadmium-rich layer will diffuse into the substrate
Implementation Method 2
where it is accelerated by the intense electric field towards the other doped region
Implementation Method 3
caused by thermal agitation that provides sufficient energy to form an electron-hole pair through spontaneous generation
Data Source
Figure 1A~1C
Figure 2A~3
Figure 4A~4F
AI summary
Photodetection device (100) comprising a semiconductor substrate (110) made of CdxHg1-xTe, with an n-doped absorption region (120), a p-doped region (130), and a concentrated well (150) located only in the p-doped region and having an average cadmium concentration that is higher than the average cadmium concentration in the n-doped region. According to the invention, the concentrated well (150) has a cadmium concentration gradient defining therein at least one intermediate gap region (151) and at least one gap strong region (152), and the intermediate gap region (151) is in direct physical contact with an electrical contact pad (170). In this way, a substantial decrease in dark current is combined with optimal collection of charge carriers.