The Mn3+/2+ acceptor level in group III nitrides

Molecular-beam-epitaxy grown GaN:Mn and AlN:Mn layers with Mn, concentrations around'. 10(20) cm(-3) were, investigated by optical absorption and photoconductivity measurements. From electron spin resonance Mn is known to be mostly present in the neutral acceptor state in GaN without codoping. This leads to a reassignment of the optical absorption features to a charge transfer from the neutral Mn3+ oxidation state, either by direct photoionization at 1.8 eV or through a, photothermal ionization process via an excited state at 1.42 eV above the Mn3+ ground state, by spin-allowed Mn3+ E-5--> T-5 internal absorption. The position of the Mn3+/2+ acceptor level at 1.8 eV above the valence-band edge of GaN makes the realization of, carrier-mediated ferromagnetism rather unlikely in GaN;Mn. (C) 2002 American Institute of Physics. [DOI: 10.1063/1.1530374].