Anomalous Hall Effect in Gd-implanted Wurtzite Al x Ga 1-x N High Electron Mobility Transistor Structures
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1111-D03-03
Anomalous Hall effect in Gd-implanted wurtzite AlxGa1-xN/GaN high electron mobility transistor structures Fang-Yuh Lo,1,a) Alexander Melnikov,2 Dirk Reuter,2 Yvon Cordier,3 and Andreas D. Wieck2 1 Department of Physics, National Dong-Hwa University, No. 1, Sec. 2, Da Hsueh Rd., Shoufeng, Hualien 97401, Taiwan 2 Lehrstuhl für Angewandte Festkörperphysik, Ruhr-Universität Bochum, Universitätsstraße 150, 44780 Bochum, Germany 3 Centre de Recherche sur l'Hétéro-Epitaxie et ses Applications, CNRS-UPR10, rue Bernard Grégory, Sophia Antipolis, 06560 Valbonne, France ABSTRACT AlxGa1-xN/GaN high electron mobility transistor (HEMT) structures grown by ammoniasource molecular beam epitaxy (MBE) are focused-ion-beam implanted with 300 keV Gd-ions at room temperature. The two-dimensional electron gas (2DEG) of these HEMT structures is located 27 nm underneath the sample surface. At 4.2 K, current-voltage characteristics across implanted rectangles show that the structures remain conducting up to a Gd-dose of 1×1012 cm-2. Anomalous Hall effect (AHE) is observed at T = 4.2 K for structures implanted with Gd, whose dose is 3×1011 cm-2. Measurements of AHE in the wide temperature range from 2.4 K to 300 K show that the magnetic ordering temperature of these structures is around 100 K. Therefore, these Gd-implanted HEMT structures containing the still conducting 2DEG, which is now embedded in a ferromagnetic semiconductor, open the possibility to polarize the electron spins. INTRODUCTION GaN is a wide direct band gap semiconductor and the base material to realize blue light emitting devices (LEDs) and laser diodes[1]. AlxGa1−xN/GaN heterostructures attracted considerable interest since mid-1990s because of their potential applications for hightemperature and high-power electronics [2-4]. GaN thin films doped with rare earth elements were first studied for developing red, green, and blue light-emitting devices [5-7] and later for their potential to fabricate GaN-based magnetic semiconductors [8-12] since the theoretical prediction that GaN-based magnetic semiconductor can exhibit ferromagnetism above RT [13, 14]. Gd-incorporated wurtzite GaN thin films were recently reported to be ferromagnetic above RT for both doping during crystal growth [8] and by ion implantation [9-12], where the Gd-implanted ones showed the ferromagnetism even without being annealed [9]. The magnetic easy plane of Gd:GaN was found to be the thin film plane, i.e., perpendicular to the growth direction, namely, the (0001) direction, and no in-plane anisotropy was reported [8-10]. Gdimplanted wurtzite AlN was also reported to be ferromagnetic above RT for the doses in the 1014 cm−2 range [11]. Moreover, the Gd-doped GaN thin films feature an extraordinary large effective magnetic moment per Gd atom peff, which is much larger than the one of elementary Gd, especially for very dilute Gd concentrations [8-10]. These properties would extend the potential applications of the GaN/AlxGa1−xN systems to spintronics, but the applicability might be limited by th
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