Study of arsenic for antimony exchange at the Sb-stabilized GaSb(0 0 1) surface M.C. Righi * , Rita Magri, C.M. Bertoni INFM National Research Center on NanoStructures and BioSystems at Surfaces and Dipartimento di Fisica, Universita ` di Modena e Reggio Emilia, Via Campi 213/A, 41100 Modena, Italy Available online 20 January 2006 Abstract In this paper we present a first-principle study on the energetics of a single As 2 molecule on GaSb(0 0 1) reconstructed surface. In order to shed light into the mechanisms of anion exchange at the Sb-rich GaSb(0 0 1) surface, we studied firstly As 2 adsorption and then As for Sb exchange. We identify a surface region where both the processes are energetically favored. The results of this twofold analysis can be combined to derive possible reaction paths for the anion exchange process. # 2005 Elsevier B.V. All rights reserved. PACS: 68.43.Bc; 71.15.Mb Keywords: Adsorption; Exchange reaction at surface; Density functional theory; III–V Compounds 1. Introduction Epitaxially grown III–V semiconductor heterostructures containing both arsenides and antimonides, such as InAs/GaSb and InAs/AlSb, have attracted considerable attention due to the variety of band alignments that are possible still maintaining a near-lattice match. This property provides enormous flexibility in designing novel electronic and optical devices. A challenging aspect of mixed arsenide and antimonide growth is controlling the composition of the interfaces that deeply influences the transport and optical properties of the heterostructure. It has been widely reported that when As 2 is incident on an antimonide surface, an anion exchange reaction occurs, with As displacing surface Sb [1,2]. This anion intermixing can not be suppressed even at very low temperature [3]. It has been speculated that the As to Sb exchange at the GaSb and AlSb surface is driven by the reduction of the system energy via formation of stronger GaAs (or AlAs) bonds in place of GaSb (or AlSb) bonds [4]. Other mechanisms, such as microscopic stress, and surface reconstruction are believed to play a role as well. However, a microscopic description of the As-for-Sb exchange process is still lacking. In this work we address this issue by applying first-principles total energy calculations at the As 2 /GaSb(0 0 1) adsorbate system. Since the problem is quite complex, involving different processes such as molecular adsorption, dissociation, and atomic exchange, here we focus on two particular aspects: (i) we consider As 2 adsorption on the GaSb(0 0 1) reconstructed surface and the interaction of the molecule with the different elements of the reconstruction and (ii) we explore different As-for-Sb exchange configurations to identify where and how anion exchange at the surface is energetically favored. 2. Method Ab initio calculations were performed within density functional theory in the local density approximation [5]. The ionic species were described by norm-conserving pseudopo- tentials, and the electronic wave functions were expanded in a plane-wave basis, with a kinetic energy cutoff of 18 Ry. The completeness of the basis was checked to accurately describe the structural and electronic properties of the GaSb bulk. The GaSb(0 0 1) surface was modeled considering both the a(4 Â 3) and b(4 Â 3) phases [6] which were found to stabilize the GaSb(0 0 1) surface for a wide range of surface preparation conditions [7]. Both the surface reconstructions contain one www.elsevier.com/locate/apsusc Applied Surface Science 252 (2006) 5271–5274 * Corresponding author. Tel.: +39 059 2055289; fax: +39 059 374794. E-mail address: mcrighi@unimo.it (M.C. Righi). 0169-4332/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2005.12.068