Optical investigation of deep defects in GaN epitaxial layers grown on 6H-SiC

Photoluminescence (PL) has been used to study GaN layers, which were grown hy the sublimation sandwich technique on 6H-SiC substrates. The promising quality of the samples, which have a lattice mismatch of 3.5%, is demonstrated by the high intensity and the small half width (2 meV) of the donor bound exciton which is comparable to that for metalorganic vapour phase epitaxy grown layers. Fourier transform infrared photoluminescence spectroscopy was used to search for 3d elements (deep defects) which are incorporated as natural contaminants during the epitaxial growth. An emission with a no phonon line at 1.3 eV was observed, which is proposed in the literature to be caused by an internal 3d transition Fe3+, and also two additional strong emissions with sharp no phonon lines at 1.19 and 1.04 eV. The PL measurements show, that the emission at 1.19 eV is due to an internal 3d transition of a d(2) system. The no phonon line at 1.04 eV belongs to an internal 3d transition of a d(1), d(2), or d(7) system, possibly Ti2+, Ti3+, V3+, or Co2+. (C) 1996 The Institute of Materials.