Transport studies of carbon-rich a-SiC x :H film through admittance and deep-level transient spectroscopy measurements

An intrinsic, carbon-rich a-SiC _x :H thin film, prepared by the plasma-enhanced chemical vapour deposition (PECVD) technique, has been studied mainly by AC admittance and small-pulse deep-level transient spectroscopy (DLTS) measurements on an Al/a-SiC _x :H/p-Si metal–insulator–semiconductor (MIS) structure. The effects of measurement temperature, voltage and small-signal AC modulation frequency on the MIS capacitor are qualitatively and quantitatively described. The kinetics of charge injection from the silicon substrate into the a-SiC _x :H film, as a function of temperature and voltage bias stresses, are reported. Nearest-neighbour and variable-range hopping mechanisms are considered. An activation energy of ～?0.09?eV, and a density of states (DOS) of about 10¹⁹?cm^?3/eV were found. The value of the DOS is in agreement with the effective interface DOS of above 10¹²?cm^?2/eV assessed by both capacitance and DLTS measurements. The frequency (or temperature) dependence of the MIS capacitor over the whole DC voltage range is considered in detail. Single- and double-step carrier exchange mechanisms between the a-SiC _x :H film and the silicon substrate, in the accumulation and depletion voltage regimes, respectively, are proposed.