Early Stages of Halogen Adsorption on Cation-Rich InAs(001): Surface Etching Mechanism A. V. Bakulin,* ,†,‡ S. E. Kulkova, †,‡ S. V. Eremeev, †,‡ and O. E. Tereshchenko §,∥ † Institute of Strength Physics and Materials Science SB RAS, 2/4 Akademichesky avenue, Tomsk, 634021, Russia ‡ National Research Tomsk State University, 36 Lenina avenue, Tomsk, 634050, Russia § Rzanov Institute of Semiconductor Physics SB RAS, 13 Lavrentieva avenue, Novosibirsk, 630090, Russia ∥ Novosibirsk State University, 2 Pirogova street, Novosibirsk, 630090, Russia * S Supporting Information ABSTRACT: Comparative theoretical study of halogens (F, Cl, I) adsorption on cation-rich ζ-InAs(001)-(4 × 2) surface was performed within the density functional theory. The energetically preferable positions for Cl and I are found on-top of In- dimerized atoms whereas F prefers to adsorb between adjacent In surface dimers. The interaction of the halogen atom with In-dimerized atoms leads to weakening of the chemical bonds between In−As surface atoms, which is the origin of the initial stage of surface etching. The larger bonds weakening was found for the more electronegative F that has a tendency to break the dimers in InAs(001) and to induce stationary etching. The trend in the bonding mechanism of halogen atoms on InAs(001) surface is found to be common for other III−V semiconductor surfaces in the cation-rich limit. ■ INTRODUCTION The interest in chemical reactions between halogens and semiconductor surfaces is related to the use of halogen- containing gases in semiconductor etching processes. 1 The atomic-precision control of semiconductor surfaces is crucial for modern technologies. Thereafter, the development of the techniques such as layer by layer removal (“digital” etching), keeping an atomically flat surface morphology, is desirable for modern surface science. For the last two decades, the halogen- etch-based techniques were intensively used to modify the surface termination of III−V semiconductors by means of halogens and halogen-containing molecules. 1−10 It is known that molecular halogens dissociatively chemisorb on the surface with the formation of relatively stable bonds with the surface atoms. The formation of monohalides is observed at low halogen concentration, furthermore di- and trihalides can be formed with increase of halogens concentration. The high electronegativity of halogens (2.66, 3.16, and 3.98 in Pauling units for iodine, chlorine, and fluorine, respectively) leads to a significant electron charge density redistribution within near- surface layers and to a weakening of the chemical bonds between surface atoms. It is believed that this condition is crucial at the initial stage of dry etching process. A III B V semiconductors are the best candidate for making atomically abrupt structures because their polar surfaces (001) and (111) represent alternating anion and cation layers. Despite numerous experimental studies, 1−3 and references therein as well as a successful realization of atomic layer-by- layer etching, 8−10 there is a lack in the microscopic description of the mechanism of halogen-semiconductor interaction. It was shown by scanning tunneling microscopy (STM) that at a low coverage iodine and chlorine atoms are adsorbed in the Ga missing row of the ζ-GaAs(001)-(4 × 2) surface, 11 where they occupy the positions between arsenic atoms. An experimental and theoretical analysis of chlorine adsorption on the GaAs(001)-c(8 × 2) surface have shown that chlorine prefers to adsorb above Ga-dimerized atoms. 12−15 Furthermore, it was shown 15 that obtained trend in the Cl geometry on ζ- GaAs(001)-(4 × 2) surface remains the same in case of Cl adsorption on ζ-InAs(001)-(4 × 2) surface. The comparative study of three halogens (F, Cl, I) on ζ-GaAs(001)-(4 × 2) surface was performed. 16 It was shown that the most stable adsorption geometries are the same for all considered halogens: halogen adatom prefers to be bonded with Ga in on-top dimer position. In contrast to GaAs, the mechanism of halogen interaction with other A III B V semiconductors is still poorly known. To the best of our knowledge, the interaction of halogens with the In- rich InAs(001) surface was not investigated earlier by first- principles calculations, except mentioned above our preliminary results. 15 In earlier studies 17−19 it was shown that the InAs(001) stable surface structure in the In-rich limit is the ζ-(4 × 2) reconstruction. In the relatively recent study, 20 the structure of InAs(001) was reexamined and new β3′-(4 × 2) reconstruction was proposed on the base of STM image analysis, however the surface energy of the new reconstruction was not compared with that of ζ-(4 × 2) there. In our recent Received: January 23, 2014 Revised: April 18, 2014 Published: April 23, 2014 Article pubs.acs.org/JPCC © 2014 American Chemical Society 10097 dx.doi.org/10.1021/jp5008208 | J. Phys. Chem. C 2014, 118, 10097−10105