Sapphire/silicon-substrate dependent magnetism of Er-substituted ZnO (ZnO: Er) thin film: x-ray absorption near edge structure (XANES) study

Abstract

Abstract Hexagonal wurtzite structure Er-substituted ZnO dilute magnetic semiconductors (DMSs) thin films have been deposited on sapphire/silicon substrate [(ZnO: Er) sapphire/silicon ] using DC sputtering technique at room temperature in oxygen-plasma atmosphere and studied their electronic/local atomic-structure and correlated with their magnetic behaviors. Incorporation of Er +3 -ion in ZnO-lattice [(ZnO: Er) sapphire/silicon ] and formation of Zn +2 /O − vacancies (V Zn /V 0 ) at the bonding between Zn and O 2 may induces room temperature ferromagnetism. Magnetic M-H loops of pure-ZnO shows diamagnetic behaviour, whereas (ZnO: Er) sapphire/silicon are ferromagnetic in nature. Moreover, (ZnO: Er) sapphire is higher ferromagnetic (saturation magnetization, M S ≈2.3 emu/g, coercivity, H C ≈63 Oe) than (ZnO: Er) silicon (M S ≈0.5 emu/g, H C ≈15 Oe). Incorporation of Er +3 -ion and formation of V Zn /V 0 vacancies were observed from x-ray photoelectron spectroscopy (XPS) and x-ray absorption near edge structure (XANES) spectroscopy analysis. The peak positions of Zn 3 p and O 1 s in XPS spectrum of (ZnO: Er) sapphire/silicon thin films are shifted at higher energy levels compared to pure ZnO, indicating that the behaviors of (ZnO: Er) sapphire/silicon thin films are substrate dependent. XANES study of Zn K -edge/Zn L 3 -edge shows the transition of Zn 1 s →4 p / Zn 2 p → Zn 4 s 3 d in antibonding states of Zn; whereas Er L 3 -edge is the transition of 2 p →5 d states of Er upon x-ray absorption that demonstrates the local atomic structure around Er in the (ZnO: Er) sapphire/silicon thin films. These transitions reveal the host-lattice in Zn-sites is substituted with Er 3+ -ions to preserve the symmetry with negligible distortion. The O K -edge shows the transition of O 2 p - Zn 4 s hybridized states through charge transfer the oxygen bands (Er-O-Zn) that reduced slightly atomic radius of Zn-O/Er-O/Zn-Zn found from extended x-ray absorption fine structure study, implies (ZnO: Er) sapphire is higher ferromagnetic behaviour than (ZnO: Er) silicon . The defect emission bands also identified through Er-substitution indicated that the emissions changed the diamagnetic-ZnO into room temperature ferromagnetic DMSs (ZnO: Er) sapphire/silicon thin film that could be useful for optoelectronic/magnetic applications.