MgZnO/ZnO quantum well nanowire heterostructures with large confinement energies

Mg(0.25)Zn(0.75)O/ZnO-quantum well nanowire heterostructures were grown with a three-step pulsed laser deposition process. To avoid shadowing effects during the coating, the ZnO nanowires were grown with a low area density on a ZnO buffer layer deposited on an a-plane sapphire substrate. By using spatially resolved cathodoluminescence measurements, the luminescence of axial and radial quantum wells were clearly distinguished. The large bandgap energy of the Mg(0.25)Zn(0.75)O barrier material (approximate to 3.85 eV) made it possible to tune the energy of quantum wells from 3.4 to 3.7 eV. The homogeneity of the radial quantum well along the wire axis was probed, revealing that only small fluctuations of about 4 meV are found in the main part of the nanowire. Near the tip of the nanowire, the energy of the radial quantum well increases due to locally modified growth conditions reducing the growth rate by up to 15%. Furthermore, the growth rates of the axial and radial quantum wells were determined, showing that the one in axial direction is a factor of about 2 larger than the one in radial direction. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3531709]