Impact Of Charge Carrier Trapping On Amorphous Selenium Direct Conversion Avalanche X-Ray Detectors

A cascaded linear system model is developed to determine the detective quantum efficiency (DQE) considering trapping of charge carriers in the absorption layer of an amorphous selenium multilayer direct conversion avalanche detector. This model considers the effects of charge carrier trapping and reabsorption of K-fluorescent X-rays on the frequency-dependent DQE(f). A 2-D simulation is performed to calculate the actual weighting potential in the absorption layer, which is used to calculate the amount of collected charge. It is observed that the DQE(f = 0) reduces from 0.38 to 0.19 due to charge carrier trapping in the absorption layer having a thickness of 1000 mu m when the electronic noise is 1500 electrons per pixel. The avalanche gain enhances the signal strength and improves the frequency dependent DQE(f) by overcoming the effect of carrier trapping and as well as the effect of the electronic noise. The simulations suggest that avalanche gain of 35 and 20 are required to overcome the effect of the electronic noise of 1500 and 700 electrons per pixel, respectively. Published by AIP Publishing.