Effect of deposition temperature on the optical transmission and paramagnetic centers in pulsed laser deposited amorphous silicon carbide thin films

Abstract

The optical transmission and paramagnetic centers in pulsed laser deposited amorphous silicon carbide films were investigated as a function of the deposition temperature (Td). As Td is raised from 200 to 650 °C, the optical gap of the films increases from about 2.0 eV up to a value of 2.2 eV, while the density of paramagnetic defects, measured by electron paramagnetic resonance (EPR), diminishes from (5.6 to 3.6)×1020 spins/cm3. EPR line shape analyses and g-value measurements indicate that the EPR active centers are clustered sp2 carbon related defects. At a measurement temperature of −190 °C, the exchange narrowed EPR linewidth, evaluated at 5.0±0.3 G, is nearly independent of Td. However, at room temperature, the EPR linewidth was found to increase with deposition temperature, thus suggesting a decrease in the size of the sp2 bonded clusters. All the structural changes revealed by EPR, as Td was raised from 200 to 650 °C, correlate well with the optical transmission data and with the increase in heteronuclear SiC bonding revealed by Fourier transform infrared spectroscopy. Finally, analysis of the thermal dependence of the EPR linewidth together with the conductivity of the a-SiC films have revealed the existence of different conduction mechanisms in the layers, depending on the deposition temperature.