DETERMINATION OF THE HYDROGEN DENSITY-OF-STATES IN AMORPHOUS HYDROGENATED SILICON

A method for determining the density of hydrogen binding energies from H evolution is presented and used to determine the hydrogen density o f states (HDOS) in amorphous silicon. The method is based on fractiona l evolution where the temperature is ramped up and down until all the H is evolved. From the evolution curves, the H chemical potential is d etermined as a function of concentration that can be related to the H density of states. The fractional evolution extraction of the HDOS is tested on simulations of evolution, and is shown to yield good estimat es of the underlying density of states. When applied to amorphous sili con, two peaks in the density of states at similar to-1.8 eV and at ab out similar to-2.2 eV below the transport level are found. A majority of the hydrogen (> 80%) resides in the shallow energy level. (C) 1998 Elsevier Science B.V. All rights reserved.