Mechanism of Interface Roughness Contribution in Heteroepitaxy

Based on experiments conducted on epitaxial GaN materials deposited on AlN substrates with varying sputtering thicknesses, this study demonstrates that the atomic behavior at the heteroepitaxial interface is influenced not only by the initial surface energy of heteroepitaxy but also by the microscopic morphology of the epitaxial surface. When the macroscopic surface energy remains constant, increased undulations in the microscopic morphology amplify disparities between in-plane and out-of-plane crystal orientations. These disparities result from differences in the dangling bonds associated with in-plane and out-of-plane crystal planes. Consequently, these variations affect the microscopic surface energy, influencing the migration and diffusion of molecules on the surface. Additionally, the unevenness of the heteroepitaxial surface physically increases resistance to molecular migration and diffusion, thereby reducing the diffusion length of the source atoms. These two factors collectively shape the molecular dynamics of nucleation at the interface, ultimately impacting the crystal quality of heteroepitaxial materials. Notably, the crystal quality of heteroepitaxial materials does not always correlate positively with the quality of the heteroepitaxial substrate. Instead, it is more directly determined by the atomic kinetic nucleation behavior at the heteroepitaxial interface. These findings provide valuable insights for optimizing and regulating the properties of group III nitrides.