Optical properties of the nonpolar a-plane MgZnO films grown on a-GaN/r-sapphire templates by pulsed laser deposition

Nonpolar (112¯0)a-plane MgZnO films were grown on different a-GaN/r-sapphire templates by pulsed laser deposition (PLD), where the growth temperature of GaN buffer layers varied from 700 °C to 1000 °C. High-quality a-plane MgZnO epitaxial film was deposited on the optimized 1000 °C a-GaN/r-sapphire template. Temperature-dependent PL measurements of a-plane MgZnO films reveal an S-type temperature dependence of the excitonic recombination energy. It is resulted that the excitons are localized in alloy-induced potential fluctuations at low temperature and the room-temperature quantum efficiency is calculated to be 9.2%. An involvement of band-tail states in the radiative recombination was considered, and a quantitative description of the blue temperature-induced shift was obtained assuming a Gaussian shape of the band tail.