Paper EM+AN+MI+SS-WeM3
Lattice-alignment mechanism of SiGe on Sapphire

Wednesday, October 24, 2018, 8:40 am, Room 101A

In the conventional heteroepitaxy processes, the deposition of dissimilar materials has been made with the same or similar crystal structure and perfect or nearly matching lattice constants, such as Ge/Si (diamond cubic), InAs/GaAs (zinc-blende), and GaN/Al₂O₃ (hexagonal/trigonal). On the other hand, the super-heteroepitaxy of two semiconductors with dissimilar crystal structures such as SiGe (diamond cubic)/Al₂O₃ (trigonal) is not readily achievable but requires scrupulous manipulation of growth conditions for single crystal formation. Epitaxial growth patterns of SiGe on r-plane and c-plane of sapphire substrates show 90^o-rotated and 60^o-rotated twin defects, respectively [1,2].

A team at NASA Langley Research Center developed a technique for super-hetero-epitaxy of single crystal SiGe growth; diamond-cubic structure of SiGe on trigonal structure of the c-plane sapphire substrate by a transformed lattice structure under a new lattice-alignment model [2]. Although the growth conditions were effective for the formation of single crystal film, how the mechanism or physics of single crystal formation of SiGe at the interface of sapphire was not theoretically and experimentally defined with the order of atomic scale level in arrangement. This work presents the interfacial image of SiGe/Al₂O₃ using high-resolution transmission electron microscope (HRTEM) to show the SiGe/Al₂O₃ interfacial bonding for superheteroepitaxy mechanism. The first two atomic layers of the SiGe are Si-rich where Si atoms match with the surface oxygen lattice of the Al₂O₃ substrate. After the Ge composition increases, the monolayer spacing is also increased due largely to the dominance of Ge composition since the lattice constant of Ge is bigger than that of Si. These results highlight the importance of a cleanliness of sapphire substrate, the Si-affinity to oxygen that ties up Si- of SiGe with the oxygen of sapphire, and eventually causing the deformation of SiGe cubic structure for super-heteroepitaxy [3]. From the essential understanding of the SiGe/Al₂O₃ interface mechanism, both low temperature SiGe super-heteroepitaxy and the III-V or II-VI semiconductor epitaxy are possible.

References:

[1] W.B. Dubbelday, K.L. Kavanagh, J. Cryst. Growth, 222 (2001), pp. 20-28.

[2] Y. Park, G.C. King, S.H. Choi, J. Cryst. Growth, 310 (2008), pp. 2724-2731.

[3] H. J. Kim, D. Adam, S. H. Choi, Acta Materialia, 145 (2018), pp. 1-7.