Effect of Substrate Temperature on the Structural, Electrical and Optical Properties of Nanocrystalline Silicon Films in Hot-Filament Chemical Vapor Deposition

Hydrogenated nanocrystalline silicon films are deposited onto glass substrates at different substrate temperatures (140–400 °C) by hot−filament chemical vapor deposition. The effect of substrate temperature on the structural properties are investigated. With an increasing substrate temperature, the Raman crystalline volume fraction increases, but decreases with a further increase. The maximum Raman crystalline volume fraction of the nanocrystalline silicon films is about 74% and also has the highest microstructural factor (R=0.89) at a substrate temperature of 250 °C. The deposition rate exhibits a contrary tendency to that of the crystalline volume fraction. The continuous transition of the film structures from columnar to agglomerated is observed at a substrate temperature of 300 °C. The optical band gaps of the grown thin films declines (from 1.89 to 1.53 eV) and dark electrical conductivity increases (from about 10⁻¹⁰ to about 10⁻⁶ S/cm) with the increasing substrate temperature.