Raman spectroscopic investigation of boron doped hydrogenated amorphous silicon thin films

Abstract

We report on the effects of hydrogen dilution and boron doping on the structural properties of amorphous silicon thin films prepared by plasma enhanced chemical vapor deposition. Raman studies were performed on samples differing in both boron concentration and hydrogen dilution of the silane precursor prepared at two growth temperatures. Changes in the transverse optical and acoustic phonon modes were analyzed to determine the effect of boron and hydrogen on short- and mid-range order of the amorphous crystal structure. The results show that, with either an increase of hydrogen dilution or growth temperature, the short- and mid-range order improves. However, the effect of growth temperature on the ability of hydrogen to improve the short- and mid-range order decreases as the growth temperature is increased. This is attributed to dissociation of weakly bonded species at higher growth temperature, leading to less hydrogen being absorbed. In addition, for fixed hydrogen dilution, an increase in boron doping results in a decrease in the short-range order due to a rearrangement of the chemical bonding in the thin film. Finally, a direct correlation is seen between the electrical resistivity and the short-range order for samples of differing hydrogen dilution grown at the higher growth temperatures.