Growth of novel wide bandgap room temperature ferromagnetic semiconductor for spintronic applications
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This work presents the development of a GaN-based dilute magnetic semiconductor (DMS) by metal organic chemical vapor deposition (MOCVD) that is ferromagnetic at room temperature (RT), electrically conductive, and possesses magnetic properties that can be tuned by n- and p-doping. The transition metal series (TM: Cr, Mn, and Fe) along with the rare earth (RE) element, Gd, was investigated in this work as the magnetic ion source for the DMS. Single- phase and strain-free GaTMN films were obtained. Optical measurements revealed that Mn is a deep acceptor in GaN, while Hall measurements showed that these GaTMN films were semi-insulating, making carrier mediated exchange unlikely. Hysteresis curves were obtained for all the GaTMN films, and by analyzing the effect of n- and p-dopants on the magnetic properties of these films it was determined that the magnetization is due to magnetic clusters. These findings are supported by the investigation of the effect of TM dopants in GaN nanostructures which reveal that TMs enhance nucleation resulting in superparamagnetic nanostructures. Additionally, this work presents the first report on the development of GaGdN by MOCVD providing an alternate route to developing a RT DMS. Room temperature magnetization results revealed that the magnetization strength increases with Gd concentration and can be enhanced by n- and p-doping, with holes being more efficient at stabilizing the ferromagnetic signal. The GaGdN films obtained in this work are single-phase, unstrained, and conductive making them suitable for the development of multifunctional devices that integrate electrical, optical, and magnetic properties.