CZT Radiation Detector Anode Contacts for Dark Current Blocking
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Solution Overview
Problem
Radiation detectors face challenges due to inherent noise signals from spontaneous electron-hole pair generation and current flow, leading to dark current and its negative impact on detector performance and readout electronics.
Innovation Solution
The implementation of a radiation detector with asymmetric contacts, specifically using cadmium zinc telluride (CZT) as the radiation-sensitive semiconductor substrate, and incorporating a semiconductor material layer like Cd1-xZnxTeyS1-y between the metallic material and the substrate to form anode electrodes, which are designed to be non-blocking for electrons and blocking for holes, and vice versa for cathode electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a radiation detector uses a semiconductor material substrate with metallic electrodes, then electrical current can be generated and detected, but dark current and noise signals increase due to spontaneous electron-hole pair generation and carrier injection
Solution Approach 1:
A semiconductor material layer (Cd1-xZnxTeyS1-y) is introduced as an intermediary between the metallic anode electrode and the radiation-sensitive semiconductor substrate. This intermediate layer acts as a blocking contact that prevents hole injection from the metal into the substrate while allowing electron collection, thereby reducing dark current without compromising radiation detection capability
Solution Approach 2:
The patent applies different material properties to different regions: the anode contact region uses a sulfide-containing semiconductor layer with specific band structure to block holes, while the bulk substrate maintains its radiation-sensitive properties. This localized modification of contact properties reduces dark current at the electrode-substrate interface without affecting the overall detector performance
2Object-generated harmful factors
If asymmetric contacts are implemented with sulfide-containing semiconductor layers, then dark current is reduced by blocking charge carrier injection, but device structure and fabrication complexity increase
Solution Approach 1:
The anode electrode structure is formed as a composite of the metallic material and the sulfide-containing semiconductor material layer. This composite structure combines the electrical conductivity of metal with the carrier-blocking properties of the sulfide semiconductor, achieving dark current reduction while maintaining electrical functionality
Solution Approach 2:
The patent modifies the chemical composition and band structure parameters of the contact layer by incorporating sulfur into the cadmium zinc telluride system (forming Cd1-xZnxTeyS1-y). This parameter change in material composition creates the asymmetric blocking behavior needed to reduce dark current
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 configuration significantly reduces dark current by effectively blocking the injection of charge carriers into the semiconductor substrate while allowing photocurrent to be collected, thereby enhancing the signal-to-noise ratio and improving detector performance.
Implementation Method 1
exposing a surface of a radiation-sensitive semiconductor material substrate to a gas containing hydrogen sulfide at an elevated temperature to form a sulfide-containing semiconductor material layer over the radiation-sensitive semiconductor material substrate
Implementation Method 2
The semiconductor material generates an electron-hole-pair cloud when a high-energy photon or particle impinges thereupon
Implementation Method 3
A bias voltage applied across an anode and a cathode induces electrons from the electron cloud to drift toward the anode, and holes toward the cathode
Data Source
AI summary
A radiation detector includes a radiation-sensitive semiconductor substrate, a cathode electrode disposed over a first surface of the radiation-sensitive semiconductor material substrate, and at least one anode electrode disposed over a second surface of the radiation-sensitive semiconductor material substrate, where the at least one anode electrode includes a semiconductor material layer including cadmium sulfide located between a metallic material and the semiconductor material substrate. In one embodiment, the radiation-sensitive semiconductor substrate includes cadmium zinc telluride (CZT), and the semiconductor material layer includes Cd1-xZnxTeyS1-y, where 0≤x≤0.5 and 0≤y≤0.5. Further embodiments include methods of fabricating a radiation detector that include exposing a surface of a radiation-sensitive semiconductor material substrate to a gas containing hydrogen sulfide at an elevated temperature to form a sulfide-containing semiconductor material layer.