Growth of high quality single crystal ZnO films on sapphire by pulsed laser ablation

The structural and optical characterizations of single crystal zinc oxide films on sapphire have been performed. The ZnO films were deposited by pulsed laser deposition in an oxygen environment. These films were annealed in oxygen for further improvement in the oxygen stoichiometry. Both as-deposited and oxygen annealed films were high quality single crystal as characterized by X-ray diffraction and transmission electron microscopy. The defect density, comprised mainly of dislocations and stacking faults, was low as compared to high quality films of III-nitrides deposited on sapphire. Under these growth conditions, the ZnO films grow two dimensionally on sapphire as opposed to GaN which grows three dimensionally. The band edge photoluminescence was found to be dominant, and an order of magnitude higher in the annealed films. Transmission measurements and the electrical resistivity of the annealed films also show the films were of high quality after annealing. It is envisaged that these improvements in the quality of the ZnO films occur as a result of reduction of oxygen vacancies and the density of point defects.