Abstract
We report on Ga-doped 3C-SiC epitaxial layers grown on on-axis (0001) 6H-SiC substrates using the vapor-liquid-solid technique and different Si1-xGax melts. The resulting samples have been investigated using secondary ion mass spectroscopy (SIMS), micro-Raman spectroscopy (mu-R) and, finally, low temperature photoluminescence (LTPL) spectroscopy. From SIMS measurements we find Ga concentrations in the range of 10(18) cm(-3), systematically accompanied by high nitrogen content. In good agreement with these findings, the mu-R spectra show that the Ga-doped samples are n-type, with electron concentrations close to 2x10(18) cm(-3). As expected, the LTPL spectra are dominated by strong N-Ga donor-acceptor pair (DAP) transitions. In one sample, a weak additional N-Al DAP recombination spectrum is also observed, showing the possibility to have accidental codoping with Ga and Al simultaneously. This was confirmed on a non-intentionally doped 3C-SiC (witness) sample on which, apart of the usual N and Al bound exciton lines, a small feature resolved at 2.35 eV comings from neutral Ga bound excitons. Quantitative analyses of the DAP transition energies in the Ga-doped and witness sample gave 346 meV for the optical binding energy of Ga acceptors in 3C-SiC against 251 meV for the Al one. The conditions for the relative observation of Ga and Al related LTPL features are discussed and the demonstration of room temperature luminescence using Ga doping is done. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3455999]