Hexagonal ZnO layers were grown by plasma assisted MBE on GaAs(111)B substrates. The substrate was chemically etched and no buffer layer was introduced. The epitaxial orientation relationships was ZnO(0001)//GaAs(111) and //GaAs[01-1]. The layer-substrate interface was investigated by transmission electron microscope (TEM) observation, and 2-3 monolayer thick contrast band was found at the interface. The lattice constant c was smaller than that of bulk ZnO and changed systematically with the layer thickness. Low temperature photoluminescence (PL) spectra was dominated by a donor bund exciton band at 3.360 eV. Another bound exciton band was found around 3.330 eV. The relative intensity of the PL bands changed with growth conditions. PL peak energies became smaller as the lattice constant c became smaller. The lattice strain dependence of the exciton energy was derived.

.55. Jk, 78.55.Et, 81.15.Hi ZnO epitaxial layers grown on GaAs(111)B substrates by plasma assisted MBE with different O/Zn flux ratios are characterized by photoluminescence (PL), X-ray diffraction (XRD) θ -2θ scan, ω scan, and reciprocal lattice mapping. Low temperature PL spectra are dominated by bound exciton bands at 3.360 eV and 3.330 eV. The 3.360 eV band is strong in samples grown under Zn-rich cindition and the 3.330 eV band is strong in samples grown under O-rich condition. The epitaxial orientation relationship is ZnO(0001)//GaAs(111) and

Heterojunction p-GaN/n-ZnO light emitting diode (LED) structure using Eu-doped ZnO (ZnO:Eu) as an active component is demonstrated in order to realize low-cost and environmentally friendly red LEDs with sharp linewidth and temperature stability against surrounding environment including operating temperature and injection current. Chemically stable Al2O3 is inserted as an electron blocking layer between p-GaN and ZnO:Eu/n-ZnO in order to facilitate the injection of carriers into the ZnO:Eu active layer. Moderate thickness of ~10 nm thick Al2O3 insertion facilitates the carrier recombination at the ZnO layer with comparatively low resistivity. Device characteristics of the p-GaN/Al2O3/ZnO:Eu/n-ZnO LED structures shows red luminescence under current injection with reversed bias voltage originated from Eu3+ ions in the ZnO host. Detailed optical characteristics of the ZnO:Eu layer in the LED structures utilizing the combined excitation emission spectroscopy measurement enables the identification of the luminescence center contributing to Eu luminescence under both indirect excitation and collisional excitation. The luminescence center contributing to Eu luminescence under indirect excitation via the ZnO host is different from that under collisional excitation, which would pave the way to understand the Eu luminescence mechanism in ZnO:Eu, and hence realize high-brightness LED structures based on rare-earth doped ZnO as an active component.