Oxygen partial pressure during vapor phase growth plays a critical role in determining the microstructure and other properties of oxides. However, it remains unclear how it affects the growth mechanism on the atomic scale. In this article, we take ZnO(0001) surface as a model case and demonstrate the influence of oxygen partial pressure on surface adsorption and diffusion of intrinsic adatoms by first-principles calculations. Two typical reconstructions of ZnO(0001) surface, denoted as $(2\times 2)$-O and $n_3$, are utilized to model the oxygen-rich condition and oxygen-poor condition, respectively. The $(2\times 2)$-O refers to the surface with an oxygen adatom in a $(2\times 2)$ supercell, while the $n_3$ stands for the surface with triangular pits of edge length $n=3$. We find that under the oxygen-rich condition in which $(2\times 2)$-O forms, adsorption of the O adatom is always more energetically favorable than the Zn adatom. Under oxygen-poor condition in which $n_3$ forms, however, the preferential adsorbate changes from O adatom to Zn adatom as the oxygen partial pressure decreases. The O adatom is less diffusive than the Zn adatom on both reconstructed surfaces. The diffusion barriers of both Zn and O on $n_3$ are higher than their counterparts on $(2\times 2)$-O. Insufficient surface diffusion leads to a high nucleation rate; therefore, a second-layer nucleus may form before the completion of the first-layer on $n_3$. It suggests that ZnO growth under oxygen-poor condition, in comparison with the oxygen-rich condition, is more likely to proceed with the three-dimensional island growth mode and result in a rougher surface.

• Received 13 June 2016
• Revised 17 February 2017

DOI:https://doi.org/10.1103/PhysRevB.96.115412