B.P. Zhang

Photoluminescence study of ZnO nanorods epitaxially grown on sapphire (112̄0) substrates

ZnO nanorods were synthesized on sapphire (1120) substrates by metalorganic vapor deposition. The rods exhibited better crystalline and optical properties than those of ZnO rods formed on sapphire (0001) substrates. The emission due to biexcitons is persistent up to ∼200 K, indicating potential for applications in biexciton-based nanoscale short-wavelength light-emitting photonic devices. The exciton–biexciton energy separation is independent of sample temperature. The band edge emission peak at room temperature is a mixture of free exciton and impurity-related transitions.

Growth of ZnO∕MgZnO quantum wells on sapphire substrates and observation of the two-dimensional confinement effect

ZnO∕MgZnO single quantum wells (QWs) in which the well width changes continuously were grown on sapphire (112¯0) substrates by metalorganic chemical vapor deposition. Photoluminescence (PL) measurement revealed two emission peaks: one is position dependent and the other is not. Polarized PL spectra obtained from cleaved facets demonstrated perfect two-dimensional features of the position-dependent emission peak. The position-dependent peak was attributed to emissions due to excitons confined in the ZnO well layer, and the position-independent peak was attributed to emissions due to excitons in MgZnO barrier layers. The width dependence of the emission energy from the ZnO QW was interpreted by a simple theoretical model. Typical PL decay time of the QW emission was 360ps at 77K. It was shorter than that of the MgZnO barrier, 470ps, due to the enhanced confinement effect in the QW.

High-quality ZnO films prepared on Si wafers by low-pressure MO-CVD

Abstract High-quality ZnO films were successfully prepared on Si wafers by low-pressure MO-CVD using zinc acetylacetonate (Zn(C5H7O2)2) and oxygen. The c-axis oriented ZnO films were grown on p-type Si wafers at temperature of 520 °C with ZnO buffers layers deposited by RF sputtering. Although, the ZnO layer deposited by sputtering has a poor c-axis orientation, the films prepared by MO-CVD on the ZnO buffer layer shows a sharp X-ray diffraction peak at 34.4° corresponding to the (0002) of hexagonal ZnO. Room temperature photoluminescence spectrum of the all film exhibits a strong peak consisted of near-band edges emission at 378 nm. Current–voltage characteristics of the ZnO(n)/Si(p) heterojunction exhibits non-linear and rectifying characteristics with a small current leakage in the reverse direction. A dark-blue light was clearly observed around the periphery of the top Al electrode by applying forward bias voltages.

Structural and optical properties of ZnO films grown on R–Al2O3 substrates

Structural and optical properties of ZnO films grown on R–Al2O3 substrates by atmospheric pressure chemical-vapor deposition were investigated using x-ray diffraction and photoluminescence. The (1120) plane of the ZnO film tilted 0.3° with respect to the (1102) plane of the substrate and rotated about 7° around the normal of the sample surface. Symmetric (1120) and asymmetric (2022) x-ray reflection on ZnO films with different thicknesses were carried out. Comparison with photoluminescence measurements allowed us to conclude that the optical properties of the ZnO films are predominately determined by the in-plane, rather than out-of-plane, structural features.

Features of nanometer scale islands on CdSe/ZnSe surfaces

We examined the early-stage (within a few hours) properties in air of nanometer scale islands formed on a CdSe/ZnSe surface. When a CdSe/ZnSe surface grown in vacuum was exposed to air, some islands were newly formed. The aspect ratio of the island was found to increase first and then decrease. A depletion zone was observed in the perimeter of the island which indicates the intermixing of ZnSe into the island. Surface analyses using Auger electron spectroscopy indicated that the island was composed mainly of oxides and the outer shell was Zn enriched and Cd depleted. This letter shows that surface oxidation plays a key role in the formation of islands on CdSe/ZnSe surfaces in atmosphere.