Structural and Raman scattering properties of ZnO:Al thin films sputter-deposited at room temperature

Structural and Raman scattering properties of Al-doped ZnO (ZnO:Al) thin films grown by radio-frequency (RF) magnetron sputtering at room temperature has been investigated. Coupled with the low temperature-deposition, the RF power was found to have profound influence on various film properties. An increase in the RF power effected an unusual deterioration of preferred c-axis orientation and increased polycrystallinity accompanied by a progressive transformation from a dense columnar to a non-columnar and faceted grain structure. Raman spectra of the films showed phonon modes at ∼274, 475 and 505 cm ^-1, which are unusual of wurtzite ZnO. The origin and evolution of these modes have been elucidated by comparing these spectra with those of undoped ZnO films grown under identical conditions and by correlating their intensity variation with RF power. It has been shown that although manifestation of all three modes is associated with the Al dopant incorporation in the films, their intensity evolution is distinctly affected by the RF power-dependent carrier concentration n and disorder in the films.