Materials Science and Engineering, B9 ( 1991 ) 137-141 137 The fabrication of a novel composite GaAs/SiO 2 nucleation layer on silicon for heteroepitaxial overgrowth by molecular beam epitaxy J. de Boeck, J. Alay, J. Vanhellemont, B. Brijs, W. Vandervorst and G. Borghs Interuniversity Micro-Electronics Centre (IMEC vzw), Kapeldreef 75, B-3GO1Leuven (Belgium) M. Blondeel and C. Vinckier Laboratory for Analytical and Inorganic Chemistry, Department of Chemistry, K. U. Leuven, 200F Celestijnenlaan, B-3001 Leuven (Belgium) Abstract We report on the fabrication of a composite GaAs-SiO 2 nucleation layer. The layer is formed by a deposition of a GaAs island layer by molecular beam epitaxy (MBE), followed by an oxidation step of the silicon regions surrounding the islands. In this way, small GaAs islands, for which the critical thickness for misfit dislocation generation is increased, are surrounded by a stable amorphous phase. Lateral overgrowth seeded by the individual GaAs islands might enhance the overall epilayer quality. We describe the fabrication and cleaning of such a composite GaAs-SiO x nucleation layer that is compatible with the epitaxy process. Preliminary regrowth on a non-optimized composite surface resulted in GaAs-on-silicon quality equal to standard GaAs-on-silicon. Compared with GaAs epitaxy on porous silicon, another seeded growth technique, the composite surface technique has greater technological potential for the monolithic integration of GaAs and silicon electronics. 1. Introduction In GaAs-on-silicon heteroepitaxy the material degradation induced by the lattice and thermal mismatch of both semiconductors has received great attention [1]. The initial stages of GaAs-on- silicon heteroepitaxy show a tendency towards strong three-dimensional nucleation [2]. Recent studies have investigated the possibility of two- dimensional growth of GaAs on silicon [3, 4]. Ideally, early two-dimensional growth is the most suitable way to improve the intrinsic materials quality, when a regular network of non-threading misfit dislocations can be formed. The critical thickness for dislocation generation in GaAs/Si is estimated to be between 2 and 4 nm [5] and inhi- bition of 60 ° dislocations is difficult to realize in practice. As is well established, the critical thickness for misfit dislocations increases significantly when the lateral dimensions of a coherently strained island are comparable to its height (0.5 < h/l< 1 ) [6]. This theoretical consideration has been con- firmed for the GaAs-on-silicon system [1] where initial GaAs islands grown at 405 °C are found to be coherently strained to heights of 6 nm. Heteroepitaxy on porous silicon has been applied [6, 7] to test the concept of small seeding areas surrounded by a non-epitaxy environment to alleviate the misfit dislocation problem. However, the above mentioned technique is not compatible with standard silicon processing and no signifi- cant GaAs-on-silicon quality improvement has yet been reported, this being ascribed to the roughness of the porous silicon substrate. With this paper we want to stimulate the study on an alternative approach: overgrowth on a composite surface (CS) consisting of GaAs seeds sur- rounded by a stable amorphous phase with low nucleation probability. We report the fabrication and cleaning of a composite GaAs-SiO2 surface that is compatible with the epitaxy process. In the next section we briefly describe the experimental conditions. In the results section, the different steps in the fabri- cation of the CS are discussed using ESCA, transmission electron microscopy and Ruther- ford back scattering (RBS) as analysis tools. 0921-5107/91/$3.50 © Elsevier Sequoia/Printed in The Netherlands