Incorporation and thermal stability of hydrogen in amorphous silicon and germanium

Abstract

Based on hydrogen evolution and secondary ion mass spectrometry measurements, the relation between incorporation and stability of hydrogen is discussed for undoped amorphous Si and Ge. In both materials, an increase of hydrogen concentration results in a decrease of H stability as monitored by an enhanced H diffusion and the appearance of void-related H surface desorption. Besides film microstructure, the hydrogen chemical potential defining the filling level of a film-specific hydrogen density of states is identified as an important parameter affecting H stability. For material with low H concentration, the H chemical potential moves with temperature and is enhanced by contact with material of high H concentration. While H surface desorption takes place for amorphous Ge at considerably lower temperature than for amorphous Si, less pronounced differences occur for H diffusion in the compact materials.