Structure and Optical Properties of ZnO Nanowire Arrays Grown by Plasma-assisted Molecular Beam Epitaxy

ZnO nanowire arrays were grown on the Si(111) substrates coated with 1 nm Au catalyst by plasma as- sisted molecular beam epitaxy (MBE) through Vapor-Liquid-Solid (VLS) growth mechanism at low temperature. Field-emission scanning electron microscope (FE-SEM) reveals that ZnO nanowire arrays grow densely and vertically to the substrate surface with the average diameter of 20−30 nm. The structure properties of ZnO nanowires are measured by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM), the results clearly show that the ZnO nanowire exhibits a typical wurtzite structure with c-axis (002) preferred orientation and good crystal quality. The diffraction peaks can be indexed to a hexagonal structure of bulk ZnO with cell constants of a = 0.325 nm and c = 0.521 nm. The spacing of the lattice fringes along the c axis of the ZnO nanowire is 0.52 nm. The room temperature photoluminescence (PL) spectrum shows that the ZnO nanowire arrays possess good photoluminscent properties with strong near band edge excitonic UV emission around 380 nm and weak defect-related emission in the visible region of 475−650 nm.