Frequency and temperature dependent electrical characteristics of P-doped nc-SiOX:H thin films

Abstract

Phosphorus-doped nc-SiOX:H films with elevated dark-conductivity and wide optical band gap are prepared via one-step low-temperature (~ 250 °C) processing, by optimizing H2-dilution [RH = H2/(He + H2)] of the (SiH4 + CO2 + PH3) precursor gasses in RF plasma-CVD. The band tail defect dynamics in covalently bonded disordered oxide-semiconductor system has been extensively studied via frequency and temperature dependent conductivity-response, impedance-characteristics, and dielectric-properties, in doped-silicon-oxygen and amorphous-nanocrystalline complex system. The temperature dependent ac-conductivity obeys the Universal Jonscher power-law and the behaviour of extracted parameters from nonlinear-fitting identifies non-overlapping small-polaron-tunnelling (NSPT) model to prevail in ac-conduction mechanism. Modelling of the impedance spectra over wide frequency range via equivalent electric circuit consisting of two parallel R||CPE connected serially, confirms individual contribution of separate nc-Si and a-SiOX:H moieties. The charge carrier density-of-states, N(EF), participating in ac-conduction at ~ 373 K and ~ 104 Hz increases from ~ 7.6 × 1015 eV−1cm−3 to ~ 1.4 ×1017 eV−1cm−3 with RH elevated from 0.1 to 0.4, corresponding to increased O-content simultaneous to reduced H-content in the Si-network possessing sequentially higher-crystallinity and wider optical band gap.