PECVD grown a-SiNx:H and a-SiCx:H films were investigated as dielectric films in the form of metal/insulator/p-silicon (MIS) structures. AC admittance of MIS structures was measured as a function of dc gate bias voltages and frequencies (1-1000 kHz) of the superimposed ac bias voltage (10mV). For each applied bias voltage (from accumulating to inverting bias regimes), temperature (7) dependence of both capacitance (C) and conductance (G/omega) were measured to investigate majority/minority carrier behavior under various frequencies omega(kHz-MHz) as parameters. C and G/omega - T - omega measurements reveal that observed pairs of capacitance steps and conductance peaks are related to traps lying on the same energy value, residing in the insulator and at the interface of insulator/semiconductor structure and differing only through capture cross-sections. On the other hand, surface band bending (0,) of silicon and activation energy (EA) deduced from the Arrhenius plot of the frequency vs. reciprocal temperature as a function of gate bias (VG) seem linearly dependent, implying that EA reflects the 0, variation. (c) 2007 Elsevier Ltd. All rights reserved.