Optical properties of ZnO thin films with/without MgO-buffer annealing were investigated by low and room temperature photoluminescence measurements. The ZnO films were grown on c-sapphire substrates by plasma-assisted molecular-beam epitaxy employing a thin MgO-buffer layer. Dislocation density of ZnO layer was reduced from 5.3 x 109 to 1.9 x 109/cm2 by annealing MgO-buffer prior to the growth of ZnO. The intensity of free exciton emission from the sample with MgO-buffer annealing was almost twice of that from the sample without annealing, while the deep level emission from the sample with MgO-buffer annealing was about 1/3 of that without annealing. The MgO-buffer annealing improves optical quality of overgrown ZnO films.

Reduction of Dislocation Density and Improvement of Optical Quality in ZnO Layers by MgO-Buffer Annealing. Goto, H., Makino, H., Setiawan, A., Suzuki, T., Harada, C., Minegishi, T., Cho, M.W., Yao, T.: Current Applied Physics, 2004, 4[6], 637-9