Effects of rf power on surface-morphological, structural and electrical properties of aluminium-doped zinc oxide films by magnetron sputtering

Aluminium-doped zinc oxide (ZnO:Al) films were prepared by magnetron sputtering at different radio-frequency powers (P-rf) of 50, 100, 150 and 200 W. The properties of the films were characterised by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Raman microscopy, and spectrophotometry with the emphasis on the evolution of compositional, surface-morphological, optical, electrical and microstructural properties. XPS spectra showed that within the detection limit the films are chemically identical to near-stoichiometric ZnO. AFM revealed that root-mean-square roughness of the films has almost linear increase with increasing P-rf. Optical band gap E-gopt of the films increases from 3.31 to 3.51 eV when P-rf increases from 50 to 200 W. A widening E-gopt of the ZnO:Al films compared to the band gap (similar to 3.29 eV) of undoped ZnO films is attributed to a net result of the competition between the Burstein-Moss effect and many-body effects. An electron concentration in the films was calculated in the range of 3.73 x 10(19) to 2.12 x 10(20) cm(-3). Raman spectroscopy analysis indicated that well-identified peaks appear at around 439 cm(-1) for all samples, corresponding to the band characteristics of the wurtzite phase. Raman peaks in the range 573-579 cm(-1) are also observed, corresponding to the A(1) (LO) mode of ZnO. (C) 2008 Elsevier B.V. All rights reserved.