Shallow optically active structural defect in wurtzite GaN epilayers grown on stepped 4H-SiC substrates

A number of wurtzite GaN epilayers directly grown on 4H-SiC (0001) misoriented by 0, 3.5degrees, 5degrees, 8degrees, and 21degrees with plasma-assisted molecular-beam epitaxy were optically characterized with photoluminescence and excitation spectra. An intense shallow-defect emission peak locating at energy position similar to70 meV lower than the near band edge emission peak at 3.47 eV is found in the emission spectra of the GaN films on 4H-SiC misoriented by 8degrees and 21degrees. Stacking mismatch boundaries are supposed to be the candidate causing the optical transition. Combined with the low-temperature photoluminescence excitation spectra of the films, the location of the electronic level induced by the structural defect is determined to be about 100 meV above the valence-band maximum of GaN. (C) 2003 American Institute of Physics.