EI_SEVIER Applied Surface Science 92 (1996) 216-221 • ,,~.~:~ : : . : ..-:::,:.~,~ ~ • . . •..,.:~...-.;~ surface science A theoretical analysis of the molecular and dissociative adsorption of H20 on GaAs(110) R. Rinc6n, F.J. Garcia-Vidal, F. Flores * Departamento de Ffsica de la Materia Condensada C-Xll, Facultad de Ciencias, Universidad Aut6noma de Madrid, E-28049 Madrid, Spain Received 14 December 1994; accepted for publication 4 March 1995 Abstract The interaction of O, H, OH and H20 with a GaAs(110) surface is analyzed using a self-consistent LCAO approach supplemented with a local density approximation. Chemisorption energies for the different species are calculated and the possibility of either molecular or dissociative adsorption for water is discussed. Our results show that water adsorbs molecularly on GaAs(ll0), with O bonded to the Ga atoms; the adsorption energy on As is smaller but the initial semiconductor surface relaxation might favour water adsorption on the anion. 1. Introduction The interaction of molecules and, in particular, water with different surfaces has been a topic of basic and practical interest for many fields [1]. Water participates in many chemical reactions and plays a crucial role in the field of electrochemistry. With semiconductors, water can be used for wet-oxidation or in solutions for surface etching. Although many experimental works have studied the properties of water absorbed on metals and semi- conductors [1], only a few papers have analyzed those systems theoretically [2]. In the case of H20 on semiconductors, we mention here the work of Ciraci and Wagners for Si [3], but, to our knowledge, no theoretical analysis of H20 on GaAs(110) exists. Regarding experimental data, this system has not been so extensively studied as H20 on Si [1,4], * Corresponding author. although a few papers discuss how water adsorbs on GaAs(110) [5-7]. The main conclusion that seems to come out of these works is that H20 mainly adsorbs molecularly on GaAs(ll0) and that its physisorbed state has an energy of around 0.7 eV. In one particu- lar case [6], it has been mentioned that H20 adsorbs dissociatively on GaAs(ll0), this conclusion had been reached by using XPS, UPS and SIMS. The aim of this paper is to present a theoretical analysis of the properties of water adsorbed on H20. We follow a self-consistent LCAO-approach supple- mented with a LDA-method to analyze the many- body properties of the initial LCAO-Hamiltonian [8,9]. Section 2 will present a brief summary of the method used in our calculations, while in Section 3 we will discuss our main results. In order to under- stand the properties of H20 on GaAs(110), we have also analyzed other cases, like O, H and OH on the same semiconductor surface. In Section 3, we will present our main results for these species and even- 0169-4332/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSDI 01 69-4332(95)00233-2