Junction capacitance studies of deep defects in undoped hydrogenated amorphous silicon

Abstract

Recent results obtained by applying two methods, drive-level capacitance profiling and transient photocapacitance spectroscopy, to the study of deep defects in undoped hydrogenated amorphous silicon (a-Si:H) are reviewed. From the first method, we illustrate how it is possible to obtain the density, energy distribution, electronic occupation and spatial distribution of light-induced metastable deep defects for a set of hydrogenated amorphous silicon samples with well-characterized impurity levels. These results strongly suggest an extrinsic carbon-related component to the degree of instability in some films. We also illustrate how a detailed comparison between transient photocapacitance and photocurrent spectra provides specific information about gap state dynamics and carrier-transport processes in a-Si:H films and, in particular, metastable changes in those properties.