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

The optical transmission and paramagnetic centers in pulsed laser deposited amorphous silicon carbide films were investigated as a function of the deposition temperature (T_d). As T_d 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 T_d. 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 T_d 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. © 2000 American Institute of Physics.