Characteristics and luminescence of Ge doped ZnO films prepared by alternate radio frequency magnetron sputtering

Ge doped ZnO films have been deposited on Si(1 0 0) substrates by alternate rf sputtering of ZnO and Ge. The effects of doping and annealing on the optical and structural properties have been investigated by means of X-ray diffraction and photoluminescence (PL) spectra. With the increasing annealing temperature, the intensity of the ZnO(0 0 2) diffraction peak increases, indicating that the crystalline quality of the film improves. The samples annealed at 800 and 1000 °C there appear the GeO and GeO2 diffraction peaks, and the intensity of the near ultra-violet emission at 395 nm increases greatly, while a weak yellow emission appears at 590 nm. The near ultra-violet emission could be attributed to the GeO color centers and exciton recombination. The yellow peak is probably related to Ge incorporated in the ZnO structure.