Optical properties of homo- and heteroepitaxial ZnO/MgxZn1-xO single quantum wells grown by pulsed-laser deposition

The optical properties of ZnO/Mg0.2Zn0.8O single quantum wells grown by pulsed laser deposition on sapphire substrates as well as on ZnO substrates were studied by photoluminescence measurements. The transition energy of the excitons shows a clear blue shift with decreasing well width due to the quantum confinement. A detailed comparison of our results with the literature indicates the lack of a stringent theory to calculate the exciton transition energies. The experimentally determined full width of half maximum (FWHM) of the luminescence of hetero- and homoepitaxial grown ZnO quantum wells compared with the calculated ones suggests that an additional contribution has to be taken into account to determine the luminescence linewidth correctly. We assume an additional alloy disorder in the quantum well itself due to the diffusion of Mg. Using time-resolved photoluminescence we found a monoexponential decay in the quantum well.