Low-temperature epitaxy of ZnO films on Si(0 0 1) and silica by reactive e-beam evaporation

Low-temperature epitaxy of ZnO films was carried out on both Si(001) and silica substrates by reactive e-beam evaporation. Growth temperature was varied between 100°C and 450°C. The optimal growth temperatures were between 200°C and 300°C for Si(001) substrates and 300°C and 350°C for silica, respectively. Structural and optical characteristics grown on both of Si and silica were compared by measurements of X-ray diffraction, Raman scattering and photoluminescence excitation (PLE) spectroscopy. X-ray diffraction showed the ZnO films grown both on Si(001) and silica substrates were all highly c-axis-oriented and their linewidth of (002) diffraction peak is significantly smaller than that measured from ZnO films deposited by magnetron sputtering. However, Raman scattering demonstrated the presence of excess zinc in the ZnO/silica structure. PLE measurements exhibited the sharp band-absorption edge and exciton absorption in the ZnO films on Si(001) and poor optical properties of ZnO on silica. PLE also revealed that the absorption characteristic near the band edge remarkably changed with the variation of oxygen content in the ZnO lattice while X-ray diffraction showed that the crystalline structures of ZnO films grown under different O2 pressure almost remained unchanged. The underlying mechanism of low-temperature epitaxy of high-quality ZnO films and its applications in electronic and optoelectronic devices are discussed.