The Effects of Magnetic Field Size on the Electronic Structure of Al-Doped ZnO Thin Films Studied by X-ray Absorption and Emission Spectroscopy



This study examines Al-doped ZnO (AZO) transparent conductive thin films prepared on glass substrate using the pulsed laser deposition method with an expanding magnetic field perpendicular to the sample surface. O K-, Zn L3-, and Al K-edge X-ray absorption near-edge structure (XANES) and X-ray emission spectroscopy (XES) were used to investigate the relationship between the effects of magnetic field size and the electronic structure of AZO thin films. Analysis of the XANES spectra showed increasing O 2p states as film resistance decreases, suggesting that the enrichment of the O 2p-dangling bond along the c-axis is the main factor affecting the electric performance of AZO thin films. Magnetic field size affects electrons itinerating from Zn atoms to Al sites through O 2p–Zn 3d and O 2p–Al 3sp hybridization and consequently weakens O 2p–Zn 3d hybridization with the downsizing of the crystallite size. XES and XANES spectra of O 2p states at the O K-edge exhibit that the conduction-band minimum affects Eg and the valence-band maximum is nearly unaffected by changes in magnetic field size. Factors affecting the resistance/electric conductivity of AZO thin films are the preferential orientation of (002) along the c-axis, the thermal/annealing effect accompanied by the changes of magnetic field size, the surface effect, energy bandgap, and the density of unoccupied O 2p-derived states.