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HL: Fachverband Halbleiterphysik

HL 20: Focus Session: Magnetic Semiconductors (jointly with MA)

HL 20.2: Vortrag

Montag, 26. März 2012, 16:45–17:00, EW 202

Magnetism and bound states of Fe in GaN : a hybrid DFT study — •Paola Alippi¹, Francesco Filippone¹, Giuseppe Mattioli¹, Aldo Amore Bonapasta¹, and Vincenzo Fiorentini² — ¹CNR-ISM, Rome, Italy — ²CNR-IOM and U of Cagliari, Italy

Transition- metal (TM) impurities in GaN hold promise for room-temperature ferromagnetism. They are also under investigation because of suspected effects of electron correlation in the localized impurity d shell as well as in host p valence states. We studied therefore neutral and charged Ga-substitutional Fe impurities in GaN via spin-polarized density-functional-theory calculations using the hybrid GGA+Hartree-Fock HSE functional.

For the neutral state, Fe induces localized states in the lower valence band, and dispersed N-Fe hybrids in the majority upper valence band, and empty minority states resonant with the Ga-like conduction band. The –1 charge state occupies and shift the latter into the gap, resulting in a (0/–1) transition level near the observed value. The +1 state has a hyper-deep (+1/0) donor level associated to a bound hole on ligand N’s, i.e. a Fe(III)+L state. This is the first theoretical evidence of such a state, supported by some as-yet-inconclusive experiments. A Bader analysis shows that Fe:GaN follows a “charge self-regulation” rule. In the –1 state, the Fe-like gap state is counterbalanced by depleted Fe valence states, and conversely the bound hole is an empty gap state appearing only in the +1 state. The population of resonant plus gap states, however, remains constant, and the charge residing on Fe hardly changes upon charging the impurity+host system.