STUDY OF LIGHT INDUCED CHANGES IN a-Si:H BY DETAILED COMPUTER MODELING OF ADMITTANCE AND DLTS

A full numerical analysis of the nonequilibrium response of a Schottkybarrier space charge region for a semiconductor with an arbitrary density of states, g(E), has been developed. These methods are applied to measurements of admittance vs temperature, thermally stimulated capacitance (TSCAP), and Deep Level Transient Spectroscopy (DLTS) of n-type a-Si:H samples in a 200°C dark annealed state (State A) as well as several partially dark annealed states following initial preparation in a light saturated state (State B). We find that changes in the admittance and DLTS spectra can be explained in detail by a lowering of the bulk Fermi energy and an increase in the density of states below midgap. Detailed pictures of g(E) obtained from DLTS spectra of two partially annealed states are presented. The quantitative relation of the Fermi energy shifts to the observed changes in g(E) is discussed.