The room-temperature epitaxial growth of ZnO thin films on NiO buffered sapphire (0001) substrate was achieved by using the laser molecular-beam-epitaxy method. The obtained ZnO films had the ultrasmooth surface reflecting the nanostepped structure of the sapphire substrate. The crystal structure at the surface was investigated in situ by means of coaxial impact-collision ion scattering spectroscopy. It was proved that the buffer-enhanced epitaxial ZnO thin films grown at room temperature had +c polarity, while the polarity of high-temperature grown ZnO thin films on the sapphire was −c. Photoluminescence spectra at room temperature were measured for the epitaxial ZnO films, showing only the strong ultraviolet emission near 380nm.

We observed strong band edge luminescence at 8.5–200 K from 200–880 nm thick InN films grown on 10 nm thick InN buffer layers on Si(001) and Si(111) substrates by electron cyclotron resonance-assisted molecular beam epitaxy. The InN film on the Si(001) substrate exhibited strong band edge photoluminescence (PL) emission at 1.814 eV at 8.5 K, tentatively assigned as donor to acceptor pair [DAP (α-InN)] emission from wurtzite-InN (α-InN) crystal grains, while those on Si(111) showed other stronger band edge PL emissions at 1.880, 2.081 and 2.156 eV, tentatively assigned as donor bound exciton [D0X(α-InN)] from α-InN grains, DAP (β-InN) and D0X (β-InN) emissions from zinc blende-InN (β-InN) grains, respectively.

We have grown and characterized epitaxial layered structure GaSe on As-passivated Si(111) and GaAs on GaSe on As-passivated Si(111) for the ultimate purpose of using the layered structure GaSe as a lattice mismatch/thermal expansion mismatch buffer layer in the GaAs on Si system. Films were grown on nominally (111) oriented Si substrates by molecular beam epitaxy and characterized by in situ reflection high energy electron diffraction, as well as by ex situ scanning electron microscopy and both plan-view and cross-sectional TEM (transmission electron microscopy). In this study, GaSe was grown epitaxially on As-passivated Si(111) substrates at 500 °C with Se/Ga BEP (beam equivalent pressure) ratios of ∼10 and ∼20. Small droplets were observed on the surface after GaSe growth. These are thought to be droplets of unreacted Ga. The density and size of the droplets decreases with the increasing Se/Ga BEP ratio. When the GaSe surface is exposed to As, the droplets become GaAs islands. Subsequent GaAs growth was carried out at 400 and 500 °C, giving the following results for 300-Å-thick films: as grown GaAs films were highly twinned, and some polycrystalline GaAs was present in the film grown at 400 °C. In situ annealing at 650 °C for 10 min reduced the density of twins in both cases. In plan-view TEM, Moiré fringes from both GaAs and GaSe are observed and show conclusively that the GaAs grew epitaxially on the GaSe without contacting the Si substrate. Cross-sectional TEM shows the interface between the Si and GaSe is not smooth on the atomic scale. In spite of this, the GaSe becomes smooth with about 2 monolayers of growth and the GaAs/GaSe interface appears to be very smooth.

For the first time, we observed strong band-edge photoluminescence at 1.814 eV, and two stronger emissions at 1.880 and 2.081 eV at 8.5 K from the respective 880 nm thick InN heteroepitaxial layers (heteroepilayers) with 10 nm thick InN buffer layers grown on Si(001) and Si(111) substrates by electron cyclotron resonance-assisted molecular beam epitaxy. The former was probably assigned as donor-to-acceptor pair (DAP(a-InN)) emission from wurtzite-InN (a-InN) crystal grains, the latter were assigned as donor bound exciton (D 0 X(a-InN)) emission, and D 0 X(b-InN) or DAP(b-InN) emission from zincblende-InN (b-InN) crystal grains, respectively. Substrate annealing before growth and the introduction of a buffer layer had strong influences on the crystal structure and crystalline quality of the initial InN heteroepilayers.

Room-temperature epitaxy of AlN thin films on sapphire (0001) substrates was achieved by pulsed laser deposition using an epitaxial NiO ultrathin buffer layer (approximately 6 nm thick). Four-circle x-ray diffraction analysis indicates a double heteroepitaxial structure of AlN (0001)/NiO(111)/sapphire (0001) with the epitaxial relationship of AlN [10-10] ‖ NiO [11-2] ‖ sapphire [11-20]. The surface morphology of room-temperature grown AlN thin films was found to be atomically smooth and nanostepped, reflecting the surface of the ultrasmooth sapphire substrate with 0.2-nm-high steps.