Excited states of Fe3+ in GaN

We report a comprehensive photoluminescence excitation (PLE) investigation of the deep iron acceptor in hexagonal GaN. PLE spectra of the Fe3+[T-4(1)(G)-(6)A(1)(S)] luminescence in semi-insulating GaN samples reveal intracenter excitation processes via excited states of the Fe3+ center. Zero-phonon lines resolved around 2.01 and at 2.731 eV are attributed to the (6)A(1)(S)-T-4(2)(G) and the (6)A(1)(S)-(4)E(G) transition, respectively. A steplike excitation structure on the low-energy onset of the Fe-3+/2+ charge-transfer band is attributed to the formation of a (Fe3+,e,h) complex at 2.888 eV. We estimate a binding energy of 280 meV locating the deep Fe-3+/2+ acceptor level 3.17 eV above the valence-band maximum. In n-type GaN samples the Fe3+ luminescence is excited by hole-transfer processes. The experimental results indicate that the internal reference rule fails for the GaN/GaAs heterostructure.