Fabrication and optical characteristics of position-controlled ZnO nanotubes and ZnO/Zn_0.8Mg_0.2O coaxial nanotube quantum structure arrays

The position-controlled growth and structural and optical characteristics o ZnO nanotubes and their coaxial heterostructures are reported. To control both the shape and position of ZnO nanotubes, hole-patterned SiO₂ growthmask layers on Si(111) substrates with GaN/AlN intermediate layers using conventional lithography are prepared. ZnO nanotubes are grown only on the hole patterns at 600°C by catalyst-free metal-organic vapor-phase epitaxy. Furthermore, the position-controlled nanotube growth method allows the fabrication of artificial arrays of ZnO-based coaxial nanotube single-quantumwell structures (SQWs) on Si substrates. In situ heteroepitaxial growth of ZnO and Zn_0.8Mg_0.2O layers along the circumference of the ZnO nanotube enable an artificial formation of quantum-well arrays in a designed fashion. The structural and optical characteristics of the ZnO nanotubes and SQW arrays are also investigated using synchrotron radiation X-ray diffractometry and photoluminescence and cathodoluminescence spectroscopy.