Abstract
Stabilized amorphous selenium (a-Se) is widely used for Digital Imaging Systems for medical applications due to its ability to be manufactured over large areas and because of its capability of relatively high charge collection efficiency. In this work we have shown the behavior of a gated selenium detector. A three-terminal photodetector is presented where the photoconductive layer is deposited on two coplanar electrodes on a corning glass substrate. These two coplanar electrodes act as the source and the drain. A third electrode is deposited on top of the photoconductor layer, which functions as the gate terminal of the device. This work investigates the feasibility of controlling the charge collection of a selenium-based photo-detector by applying voltage at the gate terminal. Three different types of structures of the three-terminal device are presented. In order to investigate the charge collection behavior both the thickness of the bulk and the distance between two electrodes have been varied. 20, 70 and 200 - micron device thicknesses were chosen while the electrode spacing was varied from 6 to 10 micron. In order to compare between the different types of devices a fixed level of electric field at 2.5 V/micron was applied across the bulk of the device. Result shows that the gate voltage can control the current-voltage transfer characteristics and is dependent on the incident radiation.
One of the two main advantages of the gated photodetectors is that they can be manufactured with a simple fabrication process. The other advantage is that the gate voltage can control charge collection, which has the potential for eliminating the thin film transistor (TFT) switches in large-area direct or indirect X-ray imaging.