Properties of MOCVD-Grown GaN:Gd Films for Spintronic Devices
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Properties of MOCVD-Grown GaN:Gd Films for Spintronic Devices Andrew G. Melton1, ZhiQiang Liu2, Bahadir Kucukgok1, Na Lu3, and Ian Ferguson1 1
Department of Electrical and Computer Engineering, University of North Carolina at Charlotte, Charlotte, NC, 28223, USA 2 R&D Center for Semiconductor Lighting, Chinese Academy of Sciences, Beijing, China 3 Department of Engineering Technology, University of North Carolina at Charlotte, Charlotte, NC, 28223, USA
ABSTRACT The mechanism leading to RT ferromagnetism in Gd-doped GaN is not agreed upon, despite many experimental and theoretical reports. Oxygen impurities have been proposed as a possible contributor to ferromagnetic behavior in GaN:Gd films. In this report, GaN:Gd thin films grown by MOCVD using two different metalorganic Gd precursors are examined. The two precursors are (TMHD)3Gd, which contains oxygen, and Cp3Gd, which does not. The films have been characterized by XRD, VSM, and EDS. EDS measurements indicate that the TMHD3Gd samples contain oxygen, while the Cp3Gd samples do not, and VSM scans show that the TMHD3Gd samples exhibit much higher magnetic moments than the Cp3Gd samples, supporting the theory that oxygen enhances the ferromagnetic behavior of GaN:Gd. INTRODUCTION Spintronics is a class of devices that utilizes electron spin in addition to charge, in order to enable enhanced and novel functionality in electronic systems. The development of practical devices is contingent on the development of ferromagnetic materials with Curie temperature (TC) above room temperature (RT). Magnetic semiconductors are of interest because they allow electron spin alignment within the device material and thus avoid spin scattering at a metalsemiconductor interface. Dilute magnetic semiconductors (DMS) consist of traditional semiconductor materials which have been doped with low densities of magnetic elements. Transition metals have been extensively studied for use in DMS, particularly Mn-doped GaAs (TC limited to 170 K) and GaN (TC > RT but electrically resistive). An alternative approach is to use rare earth (RE) elements as the magnetic centers in DMS materials. RE elements have unpaired electrons in both the d and f orbitals and thus have a higher net magnetic moment as compared to TM ions. Recently, extensive research of GaN:Gd was initiated by the observation of a very large magnetic moment of ~4000 μB/Gd atom at RT in GaN:Gd films grown by molecular beam epitaxy (MBE) [1]. The vast majority of reported GaN:Gd films are produced by either MBE or ion implantation, and these films are generally electrically resistive. Despite many reports of RT ferromagnetism in GaN:Gd material, there is not general agreement on the magnetic mechanism responsible. Interstitial oxygen (Oi) has been predicted to have a negative formation energy in GaN:Gd and to add to the net magnetic moment of the
film [2]. The authors of this work have produced the only reports of GaN:Gd thin films grown by metalorganic checmical vapor deposition (MOCVD) to date [3-5], which is the standard commer
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