Optimization of photoluminescence lifetime for ZnO films grown on ZnO substrates at low temperature

Abstract

ZnO films were grown on Zn-polar ZnO substrates with 0.5° miscut toward the [1EQ \\O(1,¯)00] direction by plasma-assisted molecular beam epitaxy (PAMBE). An atomically flat surface with one or two monolayer step height along the [0001] direction was achieved at low growth temperature. Wet etching of the substrates and ozone exposure reduced defects and improved photoluminescence (PL) lifetime by a factor of two. A 20min interval between oxygen plasma ignition and growth was found necessary for excellent crystallinity and yielded high PL lifetimes of 0.179ns. By decreasing the growth temperature in the low temperature range, the growth rate was increased from 0.02μm/h to 0.246μm/h, and correspondingly PL lifetime was improved by an order of magnitude, from 0.018ns to 0.3ns.