Paramagnetic centers in Al-doped 6H-SiC: Temperature and concentration effects

The electron paramagnetic resonance of Al-doped 6H-SiC was investigated ove r a range of temperature and concentration. The resonance signals attribute d to Al substituting for Si (Al-Si) were found to decrease sharply with tem perature between 3.4 and 6.0 K. Impurity-band conduction accounts for the a nomalous temperature behavior better than other mechanisms. Variable temper ature measurements of the Al-Si resonance provide activation energies for h opping conductivity that increase with the free-carrier concentration. The g map of Al-Si was observed to vary with [Al]. Additional resonance signals were found which increase with Al doping level. The temperature and satura tion dependence of these signals differ from those of the neutral Al-Si cen ter. One resonance having g(parallel to)=2.08 is detectable below 38 K, whi le the Al-Si signal is observed below 7 K. For free-carrier concentrations near 10(19) cm(-3), all the resonances are superimposed on a broad anisotro pic signal that exhibits complex intensity and linewidth changes with tempe rature. These additional Al-related signals were not assigned to specific m odels. (C) 2000 American Institute of Physics. [S0021-8979(00)06204-6].