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 dep osition temperature (T-d). As T-d is raised from 200 to 650 degrees C, the optical gap of the films increases from about 2.0 eV up to a value of 2.2 e V, while the density of paramagnetic defects, measured by electron paramagn etic resonance (EPR), diminishes from (5.6 to 3.6)x10(20) spins/cm(3). EPR line shape analyses and g-value measurements indicate that the EPR active c enters are clustered sp(2) carbon related defects. At a measurement tempera ture of -190 degrees C, the exchange narrowed EPR linewidth, evaluated at 5 .0 +/- 0.3 G, is nearly independent of T-d. However, at room temperature, t he EPR linewidth was found to increase with deposition temperature, thus su ggesting a decrease in the size of the sp(2) bonded clusters. All the struc tural changes revealed by EPR, as T-d was raised from 200 to 650 degrees C, correlate well with the optical transmission data and with the increase in heteronuclear SiC bonding revealed by Fourier transform infrared spectrosc opy. Finally, analysis of the thermal dependence of the EPR linewidth toget her with the conductivity of the a-SiC films have revealed the existence of different conduction mechanisms in the layers, depending on the deposition temperature. (C) 2000 American Institute of Physics. [S0021-8979(00)02122- 8].