Modeling optimal characteristics of a-Si:H semiconductor detectors for X-ray detection

The promising perspectives and important advantages of the amorphous silicon p-i-n semiconductor detectors for the direct detection of X-rays at room temperature make them suitable for medical applications. In this work, photons in the mammography energy range obtained from a molybdenum target X-ray tube, were transported in an a-Si:H diode using MCNP-4C code based on Monte Carlo method. The geometric features of p-i-n type a-Si:H diodes grown with PECVD high deposition rate technique, whose spectrometric characterization was reported in a previous work, where included in our calculations. The energy deposition profile on a structured a-Si:H detector is evaluated and the calculations are carried out for devices whose intrinsic layer thickness was varied from 5 to 50 μm. The influence of the composition and thickness of four different contact electrodes on the energy deposition process inside the intrinsic layer is described in detail. Some physical parameters of these devices are estimated and discussed in order to increase the electron-hole quote production per incident photon on the intrinsic layer and get the best X-ray detection conditions. Our results suggest that the most important geometric factor between those considered in our simulation is the thickness of the intrinsic layer, giving rise to an augmentation of ∼20% of the energy deposition in the i-layer.