AVS 50th International Symposium
    Semiconductors Thursday Sessions
       Session SC+MI-ThA

Invited Paper SC+MI-ThA1
Electronic Structure Theory of Mn-doped GaAs

Thursday, November 6, 2003, 2:00 pm, Room 321/322

Session: Ferromagnetic and Dilute Magnetic Semiconductors
Presenter: P. Mahadevan, National Renewable Energy Laboratory
Authors: A. Zunger, National Renewable Energy Laboratory
P. Mahadevan, National Renewable Energy Laboratory
Correspondent: Click to Email
(1) Orientation dependent ferromagnetism: Models involving the interaction between the transition metal spin and free carriers have conventionally been used to describe ferromagnetism in dilute magnetic semiconductors. In contrast to the expectations of such a model, we find that the GGA calculated energy of the ferromagnetic state for two 3d transition metal (TM) impurities in GaAs show a strong dependence on the crystallographic orientation of the TM pairs. For Mn in GaAs, the ferromagnetic state is strongly stabilized for pairs in the <110> direction. The stabilization is greatest along the directions for which the p-d hybridization matrix elements coupling the Mn atoms are the largest. (2) Interstitial-substitutional complexes: Examining the formation energy of Mn at various lattice sites, we find that Mn at an interstitial (Mn(i)) site could have comparable energy to Mn at a Ga site (Mn(Ga)). Under epitaxial growth conditions, the solubility of both substitutional and interstitial Mn is strongly enhanced over what is possible under bulk growth conditions. The high solubility opens the possibility of Mn atoms forming small clusters. While isolated Mn(i) are hole killers (donors), and should therefore destroy ferromagnetism, complexes such as Mn(Ga)-Mn(i)-Mn(Ga) are found to be more stable than complexes involving Mn(Ga)-Mn(Ga)-Mn(Ga). The former complexes exhibit partial or total quenching of holes, yet Mn(i) in these complexes provides a channel for a ferromagnetic arrangement of the spins on the two Mn(Ga). This suggests that ferromagnetism in Mn doped GaAs arises both from holes due to isolated Mn(Ga)as well as from strongly Coulomb stabilized Mn(Ga)-Mn(i)-Mn(Ga) clusters.