Hydrogen energetics and transport in amorphous silicon films.

Abstract

Hydrogen surface reactions and diffusion in solids are important phenomena in a variety of industrial processes. Amorphous silicon (a-Si:H), a material with tremendous potential for microelectronic applications, contains hydrogen, which is incorporated into the lattice during film growth. Understanding of hydrogen energetics and transport in amorphous silicon films is particularly important, since hydrogen has been linked to the metastable behavior of a-Si:H. Determination of hydrogen energetics in a-Si:H relies on thermally driven evolution experiments, understanding of which involves classic chemical engineering principles. The goal of the work presented in this thesis was to use mass transport, reaction, and thermodynamic theory combined with evolution experiments to determine the hydrogen density of states in amorphous silicon films. To reach this goal, two mean-field evolution models were developed. These models were compared with published evolution results, as well as glass transition measurements, and a hydrogen density of states was derived for undoped, glow-discharge deposited a-Si:H. This work represents the first successful attempt to reconcile three different types of experimental data using consistent hydrogen energetics. In addition, a novel, fractional evolution method for the determination of hydrogen density of states was developed. The mean-field evolution models were used to analyze the applicability of the fractional approach to evolution. The method was experimentally validated, using amorphous silicon carbide films, and shown capable of deriving the hydrogen density of states directly from evolution data, eliminating the need for complex modeling. Both the new fractional evolution method and the classic linear temperature programmed evolution methods were used to study dc-reactive magnetron sputtered a-Si:D films. Hydrogen densities of state consistent with the theoretical ab initio calculations were derived for the first time from the experimental results.