HETEROEPITAXY OF GASE LAYERED SEMICONDUCTOR COMPOUND ON SI(111)7X7 SUBSTRATE - A VAN-DER-WAALS EPITAXY

In a conventional heteroepitaxial system, the misfit between the lattice constants of two materials is a severe condition to overcome in order to get good heterostructures. Recently, Van der Waals epitaxy has been shown to relieve the lattice-mismatch stress by using materials which have strong bonding only in two dimensions. The Van der Waals epitaxy has so far been limited to quasi-one- or quasi-two-dimensional materials. We report, for the first time, the epitaxial growth of a GaSe layered semiconductor on Si(111)7 x 7, a substrate that is known to have active dangling bonds associated with the presence of adatoms along its surface. The film growth was performed by means of molecular-beam epitaxy and characterized in-situ by reflection high-energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS), and ex-situ by Raman spectroscopy and X-ray diffraction. It has been shown that the epitaxial growth was strongly affected by the growth conditions. At a low growth temperature range, multi-domains were observed. This has been explained according to the film growth kinetics, in which the nucleation and the growth are competing processes. At a high flux of Se, a 3D growth was observed. It is related to the decrease of the surface diffusion length of Ga adatoms. Finally, the mechanism for the epitaxial growth of GaSe on Si(111)7 x 7 is discussed in terms of the balance of surface free energy between interface, film and substrate.