Optical properties of ZnO: Al films prepared by reactive dc magnetron sputtering

Aluminium doped zinc oxide (ZnO : Al) films prepared by dc magnetron sputtering were studied in the spectral range of 300-1400 nm. The effect of post deposition heat treatments in air and in a hydrogen atmosphere on the optical properties were studied critically. The variation of refractive indices and extinction coefficients, along with the band gap due to the above, were correlated with the microstructures of the films. The presence of trap states at the grain boundaries and the number of charge carriers due to oxygen vacancies arising from absorption or desorption of oxygen seems to control the optical data in these films.