Phase transition and optical properties of Ge doped ZnO films synthesised by sputtering

Ge doped ZnO films were deposited on Si substrates by sputtering technique. With the increasing annealing temperature, the crystal quality of samples becomes gradually better and the phase transition can be observed at annealing temperature of 600°C. X-ray photoelectron spectroscopy results show the incorporation of Ge into the ZnO films with 14·81 at-%Ge content. Fourier transform infrared spectroscopy absorption spectra of samples annealed at above 600°C display vibration mode of ν (ZnO₄) and ν (GeO₄) in Zn₂GeO₄. The enhancement of ultraviolet emission intensity should be attributed to the yielded mass holes caused by Ge doping and the rising crystal quality. The sample annealed at 800°C displays the strongest blue emission due to the native defects in Zn₂GeO₄ films or/and surface defects.