The Dependence of the Magnetic Properties of GaMnN on Codoping by Mg and Si
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The Dependence of the Magnetic Properties of GaMnN on Codoping by Mg and Si Mason J. Reed2, M. Oliver Luen1, Meredith. L. Reed1 , Salah. M. Bedair1, Fevzi Erdem Arkun2, Erkan Acar Berkman2, Nadia. A. Elmasry2 ,John Zavada3 1 Electrical and Computer Engineering Department, North Carolina State University, Raleigh NC 27695-7911 2 Materials Science and Engineering Department, North Carolina State University, Raleigh NC 27695-7907 3 US Army Research Office, Durham NC 27709 ABSTRACT The magnetic properties of GaMnN, grown by metalorganic chemical vapor deposition, depend on the addition of dopants; where undoped materials are ferromagnetic, and n-type (Si-doped) and p-type (Mg-doped) films are either ferromagnetic or paramagnetic depending on dopant concentration. The ferromagnetism of this material system seems correlated to Fermi level position, and is observed only when the Fermi level is within or close to the Mn energy band. This allows ferromagnetism-mediating carriers to be present in the Mn energy band. The current results exclude precipitates or clusters as the origin of room temperature ferromagnetism in GaMnN. INTRODUCTION Dietl et al. [1] predicted that GaMnN yields ferromagnetic (FM) dilute magnetic semiconductors (DMS) with Curie temperatures above room temperature. Several groups, based on MOCVD[2,3] and MBE [4,5] growth techniques, reported these room temperature FM properties of Ga1-xMnxN, and most MBE data requires a Mn concentration above 5% to observe the ferromagnetism. For concentrations below 5%, magnetic properties were not observed. Secondary phases, which are undetectable by Xray diffraction (XRD) or high-resolution transmission electron microscopy (HRTEM), were claimed as the origin of GaMnN’s magnetic properties, but current opinion holds that FM properties are impurity or cluster related despite the undetermined origins. In this paper, we present empirical data demonstrating these magnetic properties are related solely to the Fermi-level position in GaMnN, where magnetic properties are altered by ntype or p-type doping. An explanation of the data is based on a previously reported theoretical model [6] where magnetic properties of GaMnN depend on carrier availability (related to Fermi-level position) relative to the Mn energy level [6]. B
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EXPERIMENTAL DETAILS GaMnN samples were prepared by MOCVD on (0001) sapphire substrates using TMGa, (EtCp)2Mn, and Cp2Mg as organometallic precursors. Ammonia and silane served as active nitrogen and silicon sources, respectively. All GaMnN films were grown on 1.5 µm of high resistivity GaN. Three distinct types of GaMnN films were
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grown: undoped, Si-doped, and Mg-doped. The Mn-doped layers were grown to a thickness of 0.2-0.5 µm. Secondary ion mass spectroscopy (SIMS) characterized sample composition, and xray diffraction and high resolution TEM characterized the structure. A superconducting quantum interference device (SQUID) measured the films’ magnetic response at room temperature, and Hall measurements determined electrical ch
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