Magnetotransport properties of p-type carbon-doped ZnO thin films

Abstract

Carbon-doped ZnO ͑ZnO:C͒ thin films exhibiting Curie temperature above room temperature were fabricated using ion beam technique. The magnetic moment of the ZnO:C films was found to be around 1.35 B per carbon atom. The ZnO:C films showed p-type conduction with a hole concentration of ϳ5 ϫ 10 17 cm −3 . In addition, the anomalous Hall effect and negative magnetoresistance can be detected in the ZnO:C films. The magnetotransport properties of the ZnO:C suggested that the films possessed charge carrier spin polarization. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3176434͔In recent years, there has been an intense search for ZnO-based ferromagnetic semiconductors with coexistence of ferromagnetic and spin-transport properties, which are desirable for practical spintronics applications. 1 It was predicted that Mn-doped ZnO could exhibit above room temperature ͑RT͒ ferromagnetism in a hole-rich environment. 2 This prediction initiated intensive experimental work on 3d-transition metals ͑TM͒ doped ZnO. However, the reported results have been receiving skepticism and the origin of the observed ferromagnetism continues to be strongly debated in the literature. 3 As a result, this stimulated an extensive experimental and computational search for non-TM doped ZnO, such as carbon-doped ZnO ͑ZnO:C͒ as alternatives to fabricate an unambiguous and clean ferromagnetic semiconductor. Pan et al. 4 predicted that hole mediation in ZnO:C film could lead to ferromagnetism, but ZnO:C showed n-type behavior experimentally. Thus, the intrinsic ferromagnetism in this carbon system need to be examined carefully before its potential can be explored.The origin of ferromagnetism in ZnO-based semiconductors is the most unsettled question in today's material community. This complication can be partially alleviated if the magnetotransport properties of these materials can be observed. Anomalous Hall effect ͑AHE͒ and magnetoresistance ͑MR͒ are among the most important tools to determine practical functionality of the materials as the spin polarized carrier can be probed and controlled electrically, 5 leading to direct application in electronics. Here, we demonstrate p-type ZnO:C films by investigating its ferromagnetic and magnetotransport properties. By tuning the carbon concentration in the ZnO thin films, one can control the strength of ferromagnetic coupling and its magnetotransport properties.ZnO films with a thickness of 300 nm were prepared on Si substrates at RT using the filtered cathodic vacuum arc technique. The details of ZnO film preparation have been described elsewhere. 6 The ZnO samples were mounted on a water-cooled sample holder and subsequently irradiated by Ar + ions at 45°from the normal to the surface using a Kaufman-type ion gun ͑Iontech Inc. Ltd., model 3-1500-100 FC͒ with a simultaneous supply of C atoms. For the supply of carbon, a graphite plate located perpendicularly near the ZnO sample was cosputtered with the ZnO sample by Ar + ions with an energy of 500 eV at RT. After the fabrication of ZnO:C films, ...

Stable ferromagnetism in p-type carbon-doped ZnO nanoneedles

“…4͒ and carbon-doped ZnO ͑ZnO:C͒. 5,6 Among these d 0 oxides, ZnO:C has received significant attention because of its potential application in spintronics. Peng et al 7 showed that direct hole doping at the anion site, such as C substitution on the O site, was more effective for localizing the hole and sustaining the magnetic moment.…”

“…Indeed, p-type conduction and anomalous Hall effect have been observed experimentally in ZnO:C thin films. 6 Peng et al 7 also predicted that quantum confinement effect could reduce the critical hole concentration to induce ferromagnetism in ZnO nanostructures. However, it has been proved challenging to incorporate C into ZnO nanostructures effectively by conventional methods.…”

Possible room temperature ferromagnetism in silicon doped tellurium semiconductor

“…Reported observations of ferromagnetism in the transition metal (TM) doped TiO 2 , SnO 2 , ZnO, are the most notable among them [2][3][4]. However, the role played by transition metals in manifestation of ferromagnetism in these systems has been seen with reservation after observation of ferromagnetism in ZnO with carbon-doping and even without any doping [5][6][7]. The query becomes more robust when ferromagnetism is surprisingly seen in thin films of band insulator HfO 2 even in the absence of any doping [8].…”

Effect of carbon doping on microstructure, electronic and magnetic properties of Cr:AlN films

“…Kwak et al predicted that the carbon dopants can become magnetic under confinement in ZnO nanocrystals and nanowires [7]. Herng et al obtained p-type magnetic ZnO using ion implantation [8]. Due to the polymorphism of carbon in these semiconductors, the modulation mechanisms of these properties, including carriers, local moment, and transport behaviors under magnetic field, vary significantly.…”