Transport mechanism of microcrystalline silicon thin films

The dark conductivity, σd(T), and the time-resolved microwave conductivity (TRMC) of hydrogenated microcrystalline silicon (μc-Si:H) films prepared by hot-wire chemical vapor deposition (HWCVD) and very-high-frequency plasma-enhanced CVD have been investigated. The σd(T) simulations were carried out based on a simplified energy band model. Fitting the σd(T) data indicates that the electrical transport mechanism in μc-Si:H film depends on the nanocrystallite volume fraction (Xc). Around room temperature, thermionic emission dominates for samples with low Xc, however, for high Xc, tunneling is the major conduction mechanism. In the low temperature range, the behavior of films with low-Xc is fairly explained by variable range hopping conduction. An activation energy of 0.15 eV related to oxygen was found in HWCVD films. TRMC measurements show that the mobility increases with Xc.