Hydrogen elimination model of the formation of hydrogen bonding structures during the growth of hydrogenated amorphous silicon by plasma CVD

The correlations between the [dihydride]/[monohydride] ratio and the H content in hydrogenated amorphous silicon $(a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H})$ and alloy materials were studied statistically for data obtained from infrared absorption spectroscopy. A hydrogen-elimination (HE) model, which is based on the thermally activated elimination of H atoms from ${\mathrm{SiH}}_{3}$ precursors, is proposed to describe the formation kinetics of H-Si bonding configurations during film growth. The experimental results were compared with a continuous random network (CRN) model and the HE model. It was found that $a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ deposited using a low rf power and a low ${\mathrm{H}}_{2}$-dilution ${\mathrm{SiH}}_{4}$ plasma selectively contains ${\mathrm{S}\mathrm{i}\ensuremath{-}\mathrm{H}}_{2}$ structures, while a high ${\mathrm{H}}_{2}$-dilution method reduces ${\mathrm{S}\mathrm{i}\ensuremath{-}\mathrm{H}}_{2}$ resulting in an almost random network. The selective ${\mathrm{S}\mathrm{i}\ensuremath{-}\mathrm{H}}_{2}$ formation is probably caused by the larger activation energy for H-elimination from ${\mathrm{S}\mathrm{i}\ensuremath{-}\mathrm{H}}_{2}$ rather than from Si-H. It is proposed that the ${\mathrm{H}}_{2}$-dilution effects activate the H-elimination and reconstruction of the network, and decrease ${\mathrm{S}\mathrm{i}\ensuremath{-}\mathrm{H}}_{2}$ to maximize the entropy of the arrangement of H atoms. The HE model can quantitatively describe the deposition condition dependence of the H bonding structures. Furthermore, it was suggested that the random H-elimination reactions can cause selective Si-H formation compared to the CRN model.