Development of Hydrogenated Amorphous Silicon (a-Si: H) Charge-Selective Contact Devices on a Polyimide Flexible Substrate for Dosimetry and Beam Flux Measurements
DOI:
https://doi.org/10.9734/bpi/nhstc/v2/5651Keywords:
Dosimeters, radiation detectors, charge-selective, contact devices, flexible sensorsAbstract
Hydrogenated amorphous silicon (a-Si: H) devices on flexible substrates are currently being studied for application in dosimetry and beam flux measurements. The low deposition temperature of a-Si: H allows its layering on flexible materials like polyimide (PI). The necessity of in vivo dosimetry requires thin devices with maximal transparency and flexibility. For this reason, a thin (<10 µm) a-Si: H device deposited on a thin polyimide sheet is a very valid option for this application. Furthermore, a-Si: H is a material that has an intrinsically high radiation hardness. In order to develop these devices, the HASPIDE (Hydrogenated Amorphous Silicon Pixel Detectors) collaboration has implemented two different device configurations: n-i-p type diodes and charge-selective contact devices. Charge-selective contact devices are based on a three-layer structure featuring a thin layer of metal-oxides with a small activation energy (like TiO2), a thick layer of intrinsic a-Si: H, and a thin layer of metal-oxides with a large activation energy (like MoOx or WOx). Charge-selective contact-based devices have been studied for solar cell applications, and recently, the above-mentioned collaboration has tested these devices for X-ray dose measurements. In this paper, the HASPIDE collaboration has studied the X-ray and proton response of charge-selective contact devices deposited on Polyimide.
The linearity of the photocurrent response to X-ray versus dose rate has been assessed at various bias voltages. The sensitivity to protons has also been studied at various bias voltages, and the wide range linearity has been tested for fluxes in the range from 8.3 × 107 to 2.49 × 1010 p/(cm2 s). The results show a very good linearity in the dose rate range tested, in addition to a good sensitivity and quite low leakage current below 4 V bias. Dosimetric sensitivity is related to bias voltage, in a very linear behaviour.