INTERFACE STRUCTURE OF GaSe / Si(111) STUDIED BY X-RAY STANDING WAVES. B. Capelle^*, J.F. Petroff, J.C. Boulliard, A. Koebel, Y. Zheng. Lab. Minéralogie-Cristallographie, Universtiés PARIS VI et PARIS VII, CNRS URA 09, 4 place Jussieu, 75252 Paris Cedex 05, France; ^*also at LURE, Universtié Paris-Sud, Bat 209D, 91405 Orsay Cedex, France

Recently a renew of interest for GaSe has occured in relation with the so-called Van der Waals Epitaxy (VdWE). In common heterostructures, a low misfit between the lattice constants parallel to the substrate surface is usually considered as a prerequisite. To overcome these constraints Koma et al. [1] introduced VdWE between two-dimensional (2D) materials. A 2D material has a layered structure such as GaSe. As there is no strong bonding between layers, the epitaxy of 2D / 2D materials allows the possibility to remove the constraint of the lattice mismatch between the film and the substrate.

More recently the growth of 2D materials was extended on three-dimensional (3D) semiconductor substrates like Si and GaAs. Such epitaxial growth is often referred to as "Van der Waals epitaxy" [2]. Therefore, some evidences from TEM observations [3] suggest that the growth may proceed in two stages: firstly, as in "classical" pseudomorphic epitaxy, half a GaSe layer is bonded to Si by covalent bonds and Van der Waals growth of GaSe layers occurs in a second stage. To check this assumption very thin films (approximately half a layer) of GaSe were grown on H-Si(111) substrates. The X-ray standing waves technique was used to determine the structure of the interface. XSW results confirm the existence of half a GaSe layer at the interface of GaSe / Si(111). The Ga atoms are located in T sites, straight above top Si atoms, with a Si-Ga bond length of 2.37 Å. The position of Se atoms was found to be in agreement with the one calculated from GaSe bulk structure.

[1] A.Koma, K.Sunouchi & T.Miyajima, J.Vac.Sci.Tech. B3 (1985) 724.

[2] V.Le Thanh, M.Eddrief, C.Sébenne, A.Sacuto & M.Balkanski, J. Crystal Growth 135 (1994) 1.

[3] A.Koëbel, Y.Zheng, J.F.Pétroff, M.Eddrief, V.Le Thanh & C.Sébenne, J. Crystal Growth 154 (1995) 269.