Study On Preparation And Characterization Of AlN-based Diluted Magnetic Semiconductor Thin Films

Diluted magnetic semiconductor materials (DMSs) are non-magnetic semiconductorsdoped with a few percent of magnetic elements, usually transition-metals (TM) orrare-earth-metals, and are expected to be not only easily integrable with existingsemiconductors but also highly spin-polarised. III-V based DMSs with high Curietemperature (Tc) have been investigated extensively due to its potential applications inspintronic devices. Among them, AlN has attracted much attention as promising DMSs andtheoretical studies predicted that AlN could be appropriately doped using transition metals toexhibit ferromagnetic behavior above room temperature (RT).AlN based DMSs doped with magnetic element Ni and non-magnetic element Cu havebeen prepared by magnetron sputtering. Effects of N2gas partial pressure, dopingconcentration and substrate temperature on structural, optical and magnetic properties ofdoped AlN films have been investigated. Thermal annealing effects on the structural andmagnetic properties of doped AlN films have also been discussed.Results show that Ni atoms substitute the Al in the AlN lattice when Ni concentration isless than3.14at.%. However, Ni impurity phase appeared with the doping concentrationincreasing. All doped AlN thin films exhibit room temperature ferromagnetism. The saturationmagnetization decreased with the Ni doping concentration increasing. The maximumsaturation magnetization of9emu/cm3were obtained from the Al1-xNixN films doped with3.14at.%Ni. The Curie temperature of the Al1-xNixN films were higher than350K.According to the transmission analysis, the transmittance of the film increased with N2gaspartial pressure increasing. Al1-xCuxN films prepared at room temperature were in amorphous.All Al1-xCuxN thin films showed weak ferromagnetism. The maximum Ms of Al1-xCuxN filmswas about2emu/cm3.Annealing treatment was used to improve the crystalline and magnetic properties of thefilms. Ni-doped AlN films annealed in N2atmosphere exhibited better crystalline propertiescompared to those annealed under NH3atmosphere, So did the Cu-doped AlN thin films. Results show that the crystallinity of Al1-xCuxN thin film got enhanced significantly afterthermal annealing. The saturated magnetic moment increases up to near three times incomparison with the as-prepared sample. The origin of room temperature ferromagnetism issupposed to be the combined effects of p-d hybridization mechanism and N-related defects.