Vacancy ordering at heterovalent interfaces

Atomic structures of three Ga₂Se₃ epilayers grown on GaAs(100) or ZnSe(100) epilayers by molecular beam epitaxy were studied by transmission electron microscopy. A new vacancy ordered structure was found in the heteroepitaxial interface regions of Ga₂Se₃ epilayers. The ordered structure is described as an alternate stacking of two types of Ga planes in the growth direction. One half of the sites are vacancies in one type of Ga plane, while the other type of Ga plane is fully occupied by Ga atoms. Comparison of three Ga₂Se₃ epilayers indicates a strong influence of surface chemistry of substrate epilayers on the formation of the vacancy ordering. A highly developed two-dimensional ordering has occured in the epilayer grown on a GaAs(100) surface with (4 × 3) rereconstructions.