Behavior of Al Impurity in ZnO Films: Influence of Al-Level Doping on Structure, X-Ray Photoelectron Spectroscopy and Transport Properties

Transparent and conductive ZnO:Al thin films have been deposited by a reactive magnetron sputtering using the layer-by-layer growth method. The grown Al-doped ZnO films of about 100 nm thickness on Si and glass substrates, have been investigated with respect to the crystalline phase by X-ray diffraction (XRD), surface morphology by atomic force microscopy (AFM), chemical bonding and the electronic structure by measuring the XPS core-level and valence-band spectra of the ZnO:Al films. Influence of Al content in ZnO films on structure, optical and XPS spectra, transport parameters n, µ, ρ have been studied. The weak temperature dependence of conductivity in temperature range 77-300 K suggest that Al3+ is fully ionized impurity that provides the values of electron concentration in the range 7×1019 – 2.44×1020 cm-3. Al electroactivity in ZnO films is diminishing with Al content increases. The strong decrease in Al electroactivity from 60 % to 30 % is observed for ZnO:Al films within 0.93 - 1.22 at. % of Al that indicates on enhancement of concentration of acceptor native and/or neutral complex defects in ZnO