Comparative study of microcrystalline silicon films prepared in low or high pressure regime by hot-wire chemical vapor deposition

Abstract

A comparison of structural, optical and electronic properties between undoped hydrogenated microcrystalline silicon films deposited by hot-wire chemical vapor deposition using either a high vacuum reactor or an ultra-high vacuum reactor has been made. The growth process has been assessed by changing the dilution ratio of silane in hydrogen and the process gas pressure, under the high pressure range (∼10 −1 mbar) and the low pressure range (∼10 −3 mbar) respectively. Structural properties (crystalline, amorphous and void fractions) of the films are analyzed through ultra-violet (UV)–visible ellipsometry and Raman spectroscopy data whereas electronic properties (majority carrier mobility-lifetime product and activation energy of the conductivity) are analyzed through dark conductivity and photoconductivity. All these results have been interpreted in terms of the flux of atomic hydrogen arriving on the growing surface, compared with that of radicals. This flux ratio is very sensitive to the gas pressure. This study gives better insight into the hot-wire deposition mechanisms.