Space charge capacitance spectroscopy in amorphous silicon Schottky diodes: Theory,modeling, and experiments

Numerical modeling of capacitance spectroscopy of hydrogenated amorphous silicon Schottky diodes is carried out. We test the accuracy of the determination of the density of states at the Fermi level, g(E_F), from an analytical treatment of the temperature (T) and frequency (f) dependence of the capacitance (C). Assessment of the position of the Fermi level and the attempt-to-escape frequency of states at E_F is also addressed. It is shown that the precision and reliability of the determination of g(E_F) is strongly dependent on the position of the Fermi level and the shape of the DOS and that the attempt-to-escape frequency is overestimated. Numerical calculations are then used to fit experimental capacitance data. Material parameters that provide the best fits are found in quite good agreement with independent modulated photocurrent and constant photocurrent measurements. Again, the attempt-to-escape frequency deduced from the simplified analytical treatment of capacitance data is found to be overestimated.