Using DC reaction sputtering

ZnO films were deposited on Si and quartz substrates

respectively. The reflection and transmission spectra of ZnO films have been measured in order to detect the absorption edge and absorption peaks. A special system was designed to measure the reflection spectra of ZnO films deposited on Si substrates at vertical incidence. It is found that the ZnO films deposited on Si(100) or Si(111) substrates have the same absorption edge

whose wavelength is at 370nm

corresponding to energy of 3.35eV. This value is similar to the band-gap of ZnO crystal. Measuring the transmission spectra of ZnO films deposited on quartz substrates

the absorption edge is also at 370nm. It is indicated that the band-gap of ZnO film has no variance comparing to ZnO crystal. However

the absorption edge of ZnO film deposited on Si(100) substrate is sharper then that of ZnO film deposited on Si(111) substrate. We also found that the annealed sample has sharper absorption edge then that of unannealed sample. The reason is considered to the crystallinity of ZnO film. Higher crystal quality has sharper absorption edge. In the reflection spectra

an absorption peak was observed between 550nm and 600nm. The location of absorption peak is different for the ZnO film deposited on Si(100) substrate and for the ZnO film deposited on Si(111) substrate. We suggest that it is also resulted from the the difference of crystallinity of ZnO films.