Si–H bonding in low hydrogen content amorphous silicon films as probed by infrared spectroscopy and x-ray diffraction

Abstract

A systematic series of hydrogenated amorphous silicon (a-Si:H films) has been deposited by the hot wire chemical vapor deposition (HWCVD) technique onto crystalline silicon substrates, and the H bonding has been examined by infrared spectroscopy. All deposition parameters were kept the same, except that the substrate temperature (TS) was varied to affect changes in the film H content. Although the peak position of the Si–H stretch mode changes minimally with increasing substrate temperature, the stretch mode shape changes, becoming more intense (compared to the height of the wag mode) and considerably narrower. We show, through annealing experiments, that this narrow stretch mode may be a universal feature of low H content films, and suggest interpretations for this finite (narrow) linewidth. By correlations with x-ray diffraction data, we also show that the narrowing of the stretch mode peak for low H content HWCVD films is an indication of improved lattice ordering, and suggest that this improved ordering might also exist for other types of low H content a-Si:H films as well. However, for the as-grown HWCVD films the narrowing of the stretch mode peak width at lower H contents does not completely compensate for the increase in peak height, and as a result the integrated intensity of the peak mode (relative to that of the wag mode) increases. We comment on the differences between as-grown, low H content a-Si:H HWCVD films and high H content films annealed to reduce the film H content to comparable levels, and discuss possible reasons for these intensity changes versus sample H content.