The Local Structure and I-V Characteristics of Chromium Doped Semiconducting Boron Carbide
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The Local Structure and I-V Characteristics of Chromium Doped Semiconducting Boron Carbide Jing Liu1, P. A. Dowben1, Guangfu Luo2,3, Wai-Ning Mei2, Anil Kumar Rajapitamahuni1, Andre Sokolov1, Sudarshan Karki4 and Anthony N. Caruso4 1 Department of Physics and Astronomy, University of Nebraska-Lincoln, 855 N. 16th St., Lincoln, NE 68588-0299, U.S.A. 2 Department of Physics, University of Nebraska-Omaha, Omaha, NE 68182-0266, U.S.A. 3 State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871, People’s Republic of China. 4 Department of Physics, University of Missouri-Kansas City, Kansas City, MO 64110, U.S.A. ABSTRACT The local spin configuration and band structure of chromium doped boron carbide calculated by density functional theory suggests local magnetic ordering. While the long range dopant position appears random in the boron carbide semiconductor, the local position and initial empirical/computational results suggest the promise of large magneto-resistive effects. The chromium doped boron carbide thin films, fabricated by boron carbide-chromium co-deposition, were studied by current-voltage (I-V) characteristics measurements. The results provide some reason to believe that magneto-resistive effects are indeed present at room temperature. INTRODUCTION Successful n-type doping of ß-rhombohedral boron has been accomplished with dopants such as iron [1-4], vanadium [4], chromium [4], nickel [4] and cobalt [4], while Cu is a p-type dopant [5]. For the related boron carbides, nickel [6-9] and iron [10,11] are certainly n-type dopants. In the case of cobalt, there are some indications that dominant majority carrier changes with temperature [12], so that cobalt may or may not be a p-type dopant of the boron carbides, depending upon device temperature, but this type of behavior is atypical of the transition metal dopants. The local structures of transition metal (Mn, Fe, Co) doped boron carbides thin films produced by plasma-enhanced chemical vapor deposition of orthocarborane (closo-1,2C2B10H12) and metallocenes were recently investigated by performing K-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) measurements [10-12]. The Mn, Fe and Co transition metal atoms dope boron carbide pairwise on adjacent icosahedra, which is in a good agreement with theoretical modeling of the local structure: two adjoined carborane cages each with a Mn, Fe and Co metal atom (forming the pair wise doping). The local spin configurations of all the 3d transition metal doped boron carbides, Ti through to Cu, are compared using theoretical cluster or icosahedral chain calculations [11,13]. The results suggest that transition metal doping will not only permit fabrication of boron carbide homojunctions but also may result in materials suitable for spintronic applications, particular in the case of chromium doped boron carbide [13], as suggested by other chromium metal doped materials [14]. This efforts to characterize Cr doping boron carbide
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