Characterizations of n-type ferromagnetic GaMnN thin film grown on GaN/Al2O3 (0001) by metal-organic chemical vapor deposition

A high-quality ferromagnetic GaMnN (Mn = 2.8at%) film was deposited onto a GaN buffer/Al2O3(00 01) at 885 degrees C using the metal-organic chemical vapor deposition (MOCVD) process. The GaMnN film shows a highly c-axis-oriented hexagonal wurtzite structure, implying that Mn doping into GaN does not influence the crystallinity of the film. No Mn-related secondary phases were found in the GaMnN film by means of a high flux X-ray diffraction analysis. The composition profiles of Ga, Mn, and N maintain nearly constant levels in depth profiles of the GaMnN film. The binding energy peak of the Mn 2p(3/2) orbital was observed at 642.3eV corresponding to the Mn(III) oxidation state of MnN. The presence of metallic Mn clusters(binding energy: 640.9eV) in the GaMnN film was excluded. A broad yellow emission around 2.2eV as well as a relatively weak near-band-edge emission at 3.39eV was observed in a Mn-doped GaN film, while the undoped GaN film only shows a near-band-edge emission at 3.37eV. The Mn-doped GaN film showed n-type semiconducting characteristics; the electron carrier concentration was 1.2 X 10(21)/cm(3) and the resistivity was 3.9 X 10(-3) Omega cm. Ferromagnetic hysteresis loops were observed at 300K with a magnetic field parallel and perpendicular to the ab plane. The zero field-cooled and field-cooled curves at temperatures ranging from 10 to 350K strongly indicate that the GaMnN film is ferromagnetic atleast upto 350K. A coercive field of 250 Oe and effective magnetic moment of 0.0003 mu(B)/Mn were obtained. The n-type semiconducting behavior plays a role in inducing ferromagnetism in the GaMnN film, and the observed ferromagnetism is appropriately explained by a double exchange mechanism. (C) 2009 Published by Elsevier B.V.