Effect of 900°C air annealing on luminescence properties of ZnO thin film by L-MBE

High quality preferred (0002) orientation ZnO thin films are grown on c-plane Al₂O₃ substrates by L-MBE. The samples are annealed in the air at 900°C. By comparing X-ray diffraction and photoluminescence spectra of the annealed with unannealed sample, we find that the crystalline quality and luminescence performance of the annealed samples are improved greatly. The thermal photoluminescence spectra indicates that there are three near band emitting (NBE) ultraviolet emitting peaks at 3.352, 3.309 and 3.237 eV, which are respectively due to free excitonics emitting, a exciton bounded to a neural impurity of I₉ and it's first LO phonon replica. With rising temperature, the location of the luminescence peak shifts to the long-wave ('red shift'), the full wave at half maximum (FWHM) increases; the luminescence intensity of deep level emitting (DLE) is very weak.