Iron acceptors in gallium nitride -GaN-.

We report on a combined study of the deep iron acceptor in vapour phase grown GaN epitaxial layers, on sapphire (alpha-Alsub2Osub3) substrate, by electron spin resonance (ESR) and optically detected magnetic resonance (ODMR). The ESR-spectrum of Fehigh3plus (3dhigh5) has been detected in iron-doped epitaxial layers. We assign it to deep Fe-acceptors on Ga-sites. A very similar spectrum was observed by ODMR via infrared photoluminescence (PL), also in nominally undoped GaN layers. The characteristic PL-band involved, showing rich phonon structure and rather long (about 1.5 msec) radiative lifetime occurs near 1.3 eV. We assign it to the spin-forbidden internal transition high4 Tsub1(G) correspond to high6 Asub1(S) of Fehigh3plus(3dhigh5). Photo-excitation of the 1.3 eV luminescence occurs above 2.6 eV, presumably via the charge-transfer process Fehigh3plus(3dhigh5) correspond to Fehigh2plus(3dhigh6) plus hole.