Amorphous and microcrystalline silicon films obtained by hot-wire chemical vapour deposition using high filament temperatures between 1900 and 2500°C

Abstract

The effects of hydrogen dilution and substrate temperature on the optical, transport and structural properties of silicon thin films deposited by hot-wire chemical vapour deposition using filament temperatures between 1900 and 2500°C are reported. Amorphous silicon films with a Tauc bandgap of 1·65eV, a photoconductivity-to-dark-conductivity ratio above 10⁵, a deep defect density of 10¹⁶ cm⁻³, an Urbach energy of 55 meV and a structure factor R ≈ 0·2 were prepared with deposition rates up to 40 Å s⁻¹ for hydrogen dilutions below 80%. The best properties were obtained for undiluted films deposited at a substrate temperature of 220°C. For hydrogen dilutions above 80%, microcrystalline films were obtained with low growth rates (below 3 Å s⁻¹) for all substrate temperatures studied (between 100 and 400°C) regardless of the filament temperature. The Raman spectra show a high crystalline fraction and a small grain size. In this filament temperature regime, the growth mechanism and film properties are controlled by the high flux of atomic hydrogen.