Nanostructures and optical characteristics of ZnO thin-film-like samples grown on GaN

We compared the nano-structures of three samples of ZnO thin films grown on GaN with different growth temperature conditions. Although disconnected spiral domain structures (of the order of 100?nm in width) were observed in the samples of high-temperature growth, their crystal qualities are generally better than the one grown at low temperature, either near the GaN interface or far away from the interface. In the sample of high-temperature growth through the whole process, the domain structures extend from the interface with a smaller scale and almost vertical sharp boundaries. The sample grown at the low temperature showed a generally continuous structure from the interface. However, its crystal quality is quite poor. In the sample with initial low-temperature growth and then high-temperature growth, the ZnO layer started with a continuous structure, like the sample of low-temperature growth. However, it evolved into domain structures similar to the sample of high-temperature growth beyond about 200?nm in thickness. The samples of high-temperature growth generally have higher photon emission efficiencies. The sample grown at the high temperature through the whole growth process has the highest emission quantum efficiency.