Hydrogen microstructure in amorphous hydrogenated silicon

Abstract

Using nuclear magnetic resonance (NMR) and infrared (ir) absorption spectroscopy, this paper demonstrates the effects of deposition temperature, annealing temperature, and dopant-atom incorporation on the hydrogen microstructure of plasma-deposited amorphous silicon. Multiple-quantum NMR studies indicate clusters of five to seven hydrogen atoms in films prepared at temperatures ranging from 113 to 324 \ifmmode^\circ\else\textdegree\fi{}C. In the range from 270 to 324 \ifmmode^\circ\else\textdegree\fi{}C, only these small clusters exist, but lower-temperature films also contain larger clusters. A comparison of the ir and NMR results allows the assignment of the 2080-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ absorption to small hydrogen clusters. Annealing studies indicate hydrogen rearranges prior to evolution. Deposition temperature and annealing temperature have similar effects on hydrogen concentration, but deposition temperature was found to control the density and microstructure of the film. The addition of dopant atoms also affects the hydrogen micro- structure, with phosphorous causing larger hydrogen clusters to form, and boron reducing clustering in the film. This perturbation of the film's microstructure suggests that the effects of dopant addition are much more complex in amorphous than in crystalline semiconductors. We surmise that hydrogen microstructure, rather than hydrogen content, determines amorphous-silicon properties.