Photoluminescence from Gd-implanted AlN and GaN Epilayers
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Photoluminescence from Gd-implanted AlN and GaN Epilayers John M Zavada1, Neeraj Nepal2, J. Lin2, K. H. Kim2, H. X. Jiang2, J. Hite3, G. T. Thaler3, R. M. Frazier3, C. R. Abernathy3, and S. J. Pearton3 1 Electronics Division, US Army Research Office, 4300 South Miami Blvd., Durham, NC, 27703 2 Department of Physics, Kansas State University, 116 Cardwell Hall, Manhattan, KS, 665062601 3 Materials Science and Engineering, University of Florida, Gainesville, FL, 32611 ABSTRACT Recent experiments have shown that rare earth-doped III-V nitride thin films have ferromagnetic properties that have potential impact on spintronic devices. Here we report on ferromagnetic behavior and optical spectroscopy of Gd-implanted GaN and AlN thin films. The AlN samples exhibit both luminescence and magnetic behavior at room temperature. Results indicate that magnetic and optical functionality on a single chip may be possible. INTRODUCTION Incorporation of rare earth (RE) atoms into a semiconductor host has received wide spread attention due to optoelectronic applications, such as displays, optical amplifiers, and lightemitting devices [1]. Depending upon the particular RE element, emission can be observed from the infrared (IR) through the visible to the ultra-violet (UV) region of the spectrum. Furthermore, thermal quenching of the RE-emission is significantly reduced in wide bandgap semiconductors [2]. In this regard the III-V nitrides (GaN, AlN and their alloys) are excellent hosts for RE elements. Recently there have been experimental reports of ferromagnetic (FM) behavior at room temperature in Gd-doped GaN and AlN thin films. The doping of GaN films with Gd atoms (GaN:Gd) has produced extremely large magnetic moments per RE ion [3]. Since AlGaN alloys can have very large energy bandgaps, the inner 4f shell transitions of the Gd-dopant atoms can also be observed. EXPERIMENT In this work, we have implantated Gd ions into AlN films, grown by molecular beam epitaxy (MBE), and into GaN films grown by metal-organic chemical vapor deposition (MOCVD). The samples were implanted with Gd ions at two energies with doses of either 1014 (160 keV) plus 2x1014 (320 keV) cm-2 or 2x1014 (160 keV) plus 4x1014 (320 keV) cm-2. Postimplantation annealing was performed for 5 min under a flowing N2 gas at temperatures up to 1178K. Portions of the samples were examined using a SQUID magnetometer and clear hysteretic behavior at 300K was observed [4]. Magnetic data from a Gd-implanted AlN sample is shown in Fig. 1. The magnetization (M) shows a difference between the field cooled (FC) and zero field cooled (ZFC) plots up to room temperature. There is clear evidence of hysteretic behavior at 5 K as well as at 300K. Similar magnetic behavior was measured for the Gdimplanted GaN samples. Measurements that were performed on un-implanted GaN samples did not yield any magnetic response.
Fig. 1. Field cooled (FC) and zero field cooled (FC) magnetization data from Gd implanted AlN annealed at 900∫C (left), and magnetization (M) vs. applied field (H)
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