Structural, optical, and electronic properties of room temperature ferromagnetic GaCuN film grown by hybrid physical-che
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Hyo Jin Lee and Yoon Hee Jeong Department of Physics, POSTECH, Pohang, Gyungbuk 790-784, Republic of Korea
Myung Hwa Jung Department of Physics, Sogang University, Seoul, 100-611, Republic of Korea (Received 5 September 2008; accepted 5 December 2008)
Ferromagnetic Cu-doped GaN film was grown on a GaN-buffered sapphire (0001) substrate by a hybrid physical-chemical-vapor-deposition method (HPCVD). The GaCuN film (Cu: 3.6 at.%) has a highly c-axis-oriented hexagonal wurtzite crystal structure, which is similar to GaN buffer but without any secondary phases such as metallic Cu, CuxNy, and CuxGay compounds. Two weak near-band edge (NBE) emissions at 3.38 eV and donor-acceptor-pair (DAP) transition at 3.2 eV with a typical strong broad yellow emission were observed in photoluminescence spectra for GaN buffer. In contrast, the yellow emission was completely quenched in GaCuN film because Ga vacancies causing the observed yellow emission in undoped GaN were substituted by Cu atoms. In addition, GaCuN film exhibits a blue shift of NBE emission, which could be explained with the +2 oxidation state of Cu ions, replacing +3 Ga ions resulting in band gap increment. The valance sate of Cu in GaCuN film was also confirmed by x-ray photoelectron spectroscopy (XPS) analysis. The GaCuN film shows ferromagnetic ordering and possesses a residual magnetization of 0.12 emu/cm3 and a coercive field of 264 Oe at room temperature. The unpaired spins in Cu2+ ions (d9) are most likely to be responsible for the observed ferromagnetism in GaCuN. I. INTRODUCTION
III-V-based dilute magnetic semiconductor (DMS) materials have attracted intense interest for the past two decades due to their potential ability to use two degrees of freedom, electron charge, and spin simultaneously in one device.1 This new generation of device application is called electromagnetics or spintronics, and several concepts for spintronic devices such as spin-field effect transistors, spin-light emitting diodes, magnetic randomaccess memory, and quantum computing have been proposed.2,3 In addition, DMSs have been suggested as one of the potential candidate materials for facilitating spintorque effects.4,5 To realize this technology, materials possessing ferromagnetism above room temperature are an essential priority. Carrier-induced ferromagnetism was discovered in Mn-doped GaAs, but its reported highest Curie temperature (TC) was 150 K.6 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0204
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http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 5, May 2009 Downloaded: 05 Apr 2015
Recently, a theoretical study by ab initio calculations within the local spin density approximation predicted that GaN-based DMSs would be promising candidate materials for stable ferromagnetism above 300 K,7 and some research groups have succeeded in growing DMSs dealing with Cr, Mn, or Fe in GaN at room temperature.8–10 Despite these considerable efforts, the mechanism and its universality are still under active debate because t
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