Hydrogen bonding configurations and energy band structures of hydrogenated nanocrystalline silicon films

Abstract

The correlation between the hydrogen bonding configurations and the energy band structures of hydrogenated nanocrystalline (NC) silicon films has been investiga ted. The samples were prepared by helicon wave plasma chemical vapor deposition technique. Raman scattering, infrared absorption and optical absorption measurem ents were used to analyze the microstructure, hydrogen bonding configurations an d energy band structures of the deposited films. Raman results indicate that dis tinct different structures appear in films deposited at various substrate temper atures and there is a threshold at about 200℃ for the amorphous silicon to be t ransformed to the NC phase. The energy band structures of the films are closely related to their hydrogen bonding configurations. The chemical shift of the vala nce band to the lower state induced by high hydrogen content and the structural disorder related to low substrate temperature makes the films have wide band gap s and large band tail widths. With increasing the substrate temperature, the dec rease trend of optical band and tail width is mainly related to the enrichment o f the hydrogen located in the grain boundary, which perform the function of term inating the dandling bonds at NC silicon grain surface. Further increasing the s ubstrate temperature broadens the band tail width of the films because the hydro gen content is too low to passivate the dangling bonds at the NC silicon grain s urface.