Heteroepitaxy of Layered III–VI Semiconductor GaSe on Si(111)-7×7 Surface

Abstract

The new concept of overlayer growth named van der Waals epitaxy (vdWE) emerged with the initial work of Koma [1], in which the constraints imposed by the lattice mismatch have been shown to be removed by using the layered materials. The essential requirement for vdWE is, however, that both substrate and overgrown material should have layered structure (referred 2D materials) and, as a consequence, no direct dangling bonds on their clean surfaces. Herein the forces attaching the film to the substrate are no longer mediated by chemical bonds but by the relatively weak van der Waals forces which hold the layers together. In this way, very large lattice mismatches can be tolerated due to the lack of covalent bonding across the van der Waals gap of the two materials. Relaxed films have been successfully produced with their own lattice constants of MoSe₂ on SnS₂ [1] (Δa/a=10%) and InSe on GaSe [2] (Δa/a=6,7%). It has also been shown that passivated semiconductor surfaces of three-dimensional (3D) substrates with suppressed dangling bonds are suitable to vdWE. This is the case, for example, of GaAs(111) surfaces treated by a sulfide or a selenide prior the deposition of the layered material [3].