A study of signal generation and charge collection in a-Si:H diodes for radiation imaging
Abstract
Its high radiation resistivity and large-area capability are the expected advantages of this material together with its ability to provide a front-end readout electronics in the vicinity of the sensor element. Electrons and holes created by incoming charged particles, X-rays, {gamma} rays, are drifted by the electric field inside a-Si:H diodes and this carrier movement induces signal charges on electrodes. Charge collection and signal generation process are analyzed in terms of carrier mobilities, lifetimes and electric field. Charge collection in thick a-Si:H diodes is often limited by deep-level trapping of carriers during transit and a finite charge integration time required for single particle counting in some applications and sometimes by volume recombination of carriers for detecting heavily-ionizing particles such as {alpha} particles. The charge collection process is also strongly affected by the non-uniform electric field profiles in a-Si:H diodes caused by the fixed space charges inside the material under reverse-bias. Signal generation due to a weak light pulse irradiating each end of a thick diode is measured as a function of a reverse-bias and it gives a valuable information about the fixed space charges. Field profiles can be manipulated by either doping, electrode geometry, or combination of both to improve the charge collection process. One can apply a higher reverse-bias on a diode with an equivalent thickness by providing buffer layers at each end of the…
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