Characterization of amorphous silicon deposited at high rate by helium dilution PECVD and used for applications in radiation detection

PECVD hydrogenated amorphous silicon (a-Si:H) layers have been deposited at high rates using helium dilution of the reacting precursors. This allows the fabrication of very thick layers (a few tens of microns) within reasonable processing times. This technique can be applied to the fabrication of thick p-i-n detector devices to be used for direct X-ray detection. Several p-i-n devices have been processed at deposition rates as high as 15 A/sec without significant changes in the optoelectronic properties of the a-Si:H films. Capacitance-Voltage measurements have been performed in order to measure the residual space charge density in the intrinsic region of the devices. The results demonstrate a moderate increase of the N*DoS concentration with the deposition rate. DC bias photoconductivity measurements have also been performed. The experimental data have been fitted with a multiple trapping transport model for holes. The model parameters have been studied and related to the electronic properties of the films.