Epitaxial Growth and Ultraviolet Photoluminescence of CaF 2/ZnO/CaF 2 Heterostructures on Si(111)

The epitaxial growth of zinc oxide (ZnO) nanocrystals embedded in a single-crystalline CaF2 layer on a Si(111) substrate has been demonstrated. Highly c-axis-oriented ZnO 4–10 nm thick was grown on a CaF2(111) layer using radio-frequency (RF) sputtering followed by annealing in ultrahigh vacuum, resulting in the formation of epitaxial self-organized ZnO nanocrystals on CaF2/Si(111). It was found that CaF2 can be grown epitaxially over ZnO/CaF2 by molecular beam epitaxy (MBE), thus the CaF2/ZnO/CaF2 heterostructure has been formed on a Si(111) substrate. Abrupt heterointerfaces between CaF2 and ZnO were confirmed on a transmission electron microscope (TEM) cross section, and ultraviolet (UV) photoluminescence (PL) corresponding to the band-gap energy of ZnO was dominant in PL spectra observed at room temperature.