Control of crystal polarity of ZnO and GaN epitaxial layers by interfacial engineering

The general controlling method and mechanism for the polarity of heteroepitaxial ZnO and GaN films by interfacial engineering via Plasma-assisted Molecular beam epitaxy(P-MBE) are reviewed in a viewpoint of the principle for polarity control. We proposed the principle of crystal polarity: Crystal polarity can succeed at a heterointerface when no interfacial layer is formed, while an interfacial layer with inversion symmetry is formed, the crystal polarity is inverted at the heterointerface. The effects of polarity on the growth evolution, interface, surface and bulk structure, and structural, optical, and electrical properties of ZnO and GaN epitaxy are also included. We demonstrate recent successful experimental results in selective MBE growth of ZnO on sapphire, ZnO on GaN, and GaN on ZnO, based on the proposed principle for control of crystal polarity. Additionally, the electrical characteristics such as electron concentration, band-line-up, C-V characteristics and electron trap centers of ZnO/GaN heterointerface will be discussed.