Lattice-alignment mechanism of SiGe on Sapphire

Abstract Heteroepitaxy of silicon germanium (SiGe) prepared on a sapphire substrate (Al2O3) requires scrupulous attention to growth conditions. Previous work was used a substrate temperature of 890°C to grow a SiGe (111) film on the trigonal sapphire (0001) substrate without twin defects. Although the growth conditions were effective for the formation of single crystal film, how the formation of SiGe at the interface of sapphire was not experimentally defined with the order of atomic arrangement. This work presents high resolution transmission electron microscope (TEM) images of the SiGe/Al2O3 interface to show the SiGe/Al2O3 interface bonding for heteroepitaxy mechanism. The first two monolayers of the SiGe are Si-rich as this match with the surface oxygen lattice of the Al2O3 substrate. After the Ge composition increases, the monolayer spacing also increased while maintaining the cubic crystal structure. These results highlight the importance of a cleanliness of sapphire substrate, the Al2O3 termination for SiGe growth, and the cubic structure deformation of SiGe for heteroepitaxy. From the essential understanding of the SiGe/Al2O3 interface and growth mechanism, both low temperature SiGe heteroepitaxy and the III-V or II-VI semiconductor epitaxy are possible.