DLTS response due to localized states in hydrogenated amorphous silicon

Abstract

Abstract The transient response of the localized states in a-Si : H involved in DLTS measurements is analyzed in the frame of a detailed model for the band bending. The model is based on an exponential distribution of the density of states, spatially uniform throughout a Schottky-barrier depletion layer. The thermally emitted charge is calculated and compared with the estimate of the charge from the simple crystalline model to assess the effect of nonparabolic band bending. The influence of spatially nonuniform space charge density and uncompensated shallow level concentration is analyzed by calculating the DLTS signal and retrieving the density of states by the modified crystalline model. Our results show that the simple modified crystalline model accurately determines the localized density of states in a-Si:H from DLTS data obtained with large reverse bias voltages. for lower reverse bias voltages the analysis of the DLTS spectra based on the crystalline model yields substantially lower values for the minimum density of states.