Mn valence state mediated room temperature ferromagnetism in nonpolar Mn doped GaN

Abstract In this work, we demonstrate room temperature ferromagnetism in nonpolar, m-plane manganese doped gallium nitride (m-GaN:Mn) epitaxial thin films synthesized using plasma-assisted molecular beam epitaxy on nonpolar, m-plane sapphire (Al2O3) substrates. We observed that Mn doping concentration plays a key role in stabilizing the valence state of Mn ions thereby influencing the magnetic and transport properties. Chemical characterization by X-ray photoelectron spectroscopy, X-ray absorption near edge spectra, and energy dispersive X-ray spectroscopy affirm homogeneous valence state Mn+3 in lightly doped samples, while higher doping levels cause a heterogeneous Mn+0 and Mn+2 mixed valence states. Magnetic measurements indicate that films with low doping levels show the signature of room temperature ferromagnetism, while films with higher doping show antiferromagnetic/spin glass behavior besides the indication of MnGa alloys. Temperature dependent resistivity measurements show that both the samples are semiconducting with deep level defect states. Our findings suggest the possibility of incorporating spin functionality in non-polar optoelectronic devices.