Investigation of Electrical Transport in PECVD Grown a-SiCx:H Thin Film

Abstract

Dc/ac transport characteristic of PECVD grown hydrogenated amorphous silicon carbide (a-SiCx:H) thin film was investigated in MIS (metal/insulator/semiconductor) structure by dc current/voltage (I/V) at different temperature (T), ac admittance vs. temperature at constant gate bias voltages and deep level transient spectroscopy (DLTS), respectively. According to I-V-T analysis, two main regimes exhibited. At low electric field, apparent Ohm’s law dominated with Arrhenius type thermal activation energy (EA) around 0.4 eV in both forward and reverse directions. At high field, on the contrary, space charge limited (SCL) current mechanism was eventual. The current transport mechanisms and its temperature/frequency dependence were interpreted by a thermally activated hopping processes across the localized states within a-SiCx:H thin film since 0.4 eV as EA was not high enough for intrinsic band conduction. Instead, transport of charge carriers took place in two steps; first a carrier is thermally excited to an empty energy level from an occupied state then multi-step tunnelling or hopping starts over. Therefore, the two steps mechanisms manifested as single activation energy, differing only through capture cross sections. In turn, two steps in capacitance together with conductance peaks in C-(G)-T while convoluted DLTS signal associated with such events in the measurements.