ADSORPTION, DIFFUSION AND GROWTH MODE OF ZnO THIN FILM FROM FIRST PRINCIPLES

A heteroepitaxial growth model of the ZnO film on sapphire (0001) is calculated by using a plane wave ultrasoft pseudo-potential method based on density functional theory. It is found that interfacial atoms have different diffusivity at 400°C, 600°C and 800°C. The temperature has a decisive effect on the surface and interface structures of ZnO/α-Al₂O₃ (0001) and on the growth mode of ZnO thin films. In the whole process of the adsorption and growth of ZnO, the diffusivity of O atoms is higher than that of Zn, and the interlayer diffusion has an important impact on the homogeneous growth of thin films. There are two growth modes of ZnO on sapphire (0001), which is further demonstrated by theoretical calculation. The growth mode at about 400°C has a character of mainly spiral-twisted growth with Zn-hexagonal symmetry structure, and it is favorable for forming the Zn-terminated surface. But in the case of 600°C, a regular in-plane growth is observed, which facilitates the O-terminated surface of the ZnO thin film. It can be observed from the calculation that the vacancies of Zn where the atomic layer is near to the α-Al₂O₃ (0001) surface is more than that of O atoms.