Role of hydrogen in controlling the growth of μc-Si:H films from argon diluted SiH₄ plasma

Abstract

Hydrogenated microcrystalline silicon thin films have been prepared by the rf glow discharge method using argon as a diluent of SiH₄ to achieve a high growth rate. μc-Si:H film having conductivity ~10^-5S cm^-1 was achieved at a deposition rate of 36 Å/min at a moderate power density of 90 mW/cm², without hydrogen dilution. Micrograins were identified with several well defined crystallographic orientations. Inhomogeneity and porosity at the grain boundary zone have a significant effect on the electrical properties of the films due to adsorption when exposed to atmosphere. However, by adding hydrogen to the Ar-diluted SiH₄ plasma, a homogeneous and improved network structure without having any effect of adsorption was obtained at a reduced deposition rate. Highly conducting (σ_D~10^-3 S cm^-1) undoped µc-Si:H film was prepared at a deposition rate of 15 Å/min having 90% crystalline volume fraction. The energy released by the de-excitation of Ar in the plasma initiates rapid nucleation in the Si network and atomic hydrogen in the plasma helps in the defect elimination, structural reorientation, and grain growth.