XPS and X-ray diffraction studies of aluminum-doped zinc oxide transparent conducting films

Aluminum-doped zinc oxide transparent conducting films are prepared by spray pyrolysis at different dopant concentrations. These films are subsequently characterized by X-ray diffractometric and X-ray photoelectron spectroscopic (XPS) techniques. The results are compared with those obtained from pure zinc oxide films prepared under identical conditions. X-ray diffraction measurements show an increase in lattice parameters (c and a) for aluminum-doped films while their ratio remains the same. This study also indicates that within the XPS detection limit the films are chemically identical to pure zinc oxide. However, a difference in the core-electron line shape of the Zn 2p(3/2) photoelectron peaks is predicted. An asymmetry in Zn 2p(3/2) photoelectron peaks has been observed for aluminum-doped films. The asymmetry parameters evaluated from core-electron line-shape analysis yield a value of the order of 0.04 +/- 0.01. The value is found to lie between those obtained for pure zinc oxide and has been attributed to the presence of excess zinc in the films.