Magnetic properties of Mn-doped GaN, InGaN, and AlGaN
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Magnetic properties of Mn-doped GaN, InGaN, and AlGaN M.L. Reed, E.A. Berkman*, M.J. Reed*, F.E. Arkun*, T. Chikyow**, S.M. Bedair, J.M. Zavada*** and N. A. El-Masry* Department of Electrical and Computer Engineering, North Carolina State University Raleigh, NC 27695-7911 *Department of Materials Science and Engineering, North Carolina State University Raleigh, NC 27695-7911 **National Institute for Material Science (NIMS), Nanomaterial Research laboratories, Nanoassembly R.G 1-2-1 Sengen Tsukuba Ibaraki 305-0047 Japan ***U.S. Army Research Office, Research Triangle Park, North Carolina 27709 ABSTRACT We report on the growth and magnetic properties of single crystal Mn-doped GaN, InGaN, and AlGaN films. The III-Nitride films were grown by MOCVD, while the Mn doping was performed by solid-state diffusion of a surface Mn layer deposited by pulsed laser ablation. Mndoped InxGa1-xN films were grown with x < 0.15, where the easy axis of magnetization rotates from in-plane to out-of-plane by changing the InxGa1-xN thickness/strain-state of the film from compressively strained to relaxed. Mn-doped AlxGa1-xN films were grown with x < 0.40 showing ferromagnetic behavior above room temperature. SQUID measurements ruled out superparamagnetism within these films. By optimizing the growth and annealing conditions of Mn-doped III-Nitrides, we have achieved Curie temperatures in the range of 228 to 500K. These ferromagnetic Mn-doped III-Nitride films exhibit hysteresis with a coercivity of 100-500 Oe. TEM analysis showed no secondary phases within these films. INTRODUCTION Dilute magnetic semiconductors (DMS) have potential as a new class of spintronic devices which utilize both information processing and data storage within one material system. In these materials a sizable number of nonmagnetic cations are replaced by magnetic ions to facilitate ferromagnetic behavior. Recently, researchers have focused on doping II-VI1,2 and III-V3-5 compound semiconductors with 3d transition elements to produce ferromagnetic semiconductors. EXPERIMENTAL GaN, InxGa1-xN and AlxGa1-xN films were grown by metal-organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates in an inductively-heated vertical reactor. Trimethylgallium (TMGa), ethyldimethylindium (EDMIn), trimethylaluminum (TMAl), and NH3 were used as precursors. A typical two-step sequence for III-Nitride growth was used in which a thin low temperature GaN nucleation layer is used to enhance two-dimensional growth of a high quality GaN or AlxGa1-xN epilayers subsequently deposited at ~1000 ºC on the nucleation layer. InxGa1-xN films (0
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