Sensitivity in polycrystalline HgI2 X-ray imagers for mammography

The sensitivity of polycrystalline HgI2 (poly-HgI2 ) X-ray detector is determined. A generalized expression for charge carrier transport and absorption-limited sensitivity of X-ray photoconductors is derived by analytically solving the continuity equation for both holes and electrons considering the drift of electrons and holes in the presence of deep traps. Sensitivity is studied as a function of varying applied electric field across the photoconductor for both positive and negative bias under mammographic condition. The theoretical model is fitted to the published results for physical vapor deposited (PVD) poly-HgI2 mammographic detector. The fitted values of the electron and hole ranges are 1.6896 × 10(-5)cm2V-1 and 5.916 × 10(-6)cm2V-6 respectively. Concentration of deep trap for electrons and holes were found out to be 2.6082 × 1013/cm3 and 3.3806 × 1012/cm3 respectively . Effect of decreasing electron and hole lifetime on sensitivity is studied for varying detector thickness for positive bias under mammmographic condition. Under these conditions, deteriorating hole lifetime has much more impact on sensitivity than deteriorating electron lifetime. Presence of an optimum detector thickness has been found at low hole lifetime.