Boron doping effects and microcrystallite formation in SiC:H films prepared using ECR-CVD

Abstract

Hydrogenated silicon carbide films (SiC:H) were deposited using the electron cyclotron resonance plasma chemical vapour deposition (ECR-CVD) method from a mixture of methane, silane and hydrogen, with diborane as the doping gas. The tubular vessel used had a substrate receiver circular area of 87cm 2 and was fitted with magnetic coils to guide the microwave power into the deposition section. The effect of changes in the diborane fraction on the deposition rate, optical bandgap, and electrical conductivity and its activation energy were investigated. Raman scattering analysis showed that films deposited at a low microwave power of 150 W (2.45 GHz) were largely amorphous and the bandgap decreased as the diborane fraction was increased, but films deposited at 800 W and low diborane fractions were highly conductive and contained microcrystalline silicon inclusions. The films became amorphous as the diborane fraction was increased, while the optical bandgap remained relatively unchanged throughout the diborane fraction range. The activation energy varied in an opposite manner to the change in the electrical conductivity.