Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc Full length article Microscopic mechanisms of Si(111) surface nitridation and energetics of Si 3 N 4 /Si(111) interface T.L. Petrenko a, ⁎ , V.P. Bryksa a , I.V. Dyka a , V.P. Kladko a , A.E. Belyaev a , A.V. Kuchuk b a Institute of Semiconductor Physics, NASU, 45 Prospect Nauky, 03028 Kyiv, Ukraine b Institute for Nanoscience and Engineering, University of Arkansas, West Dickson 731, Fayetteville, AR 72701, United States of America ARTICLE INFO Keywords: Si(111) surface Thermal nitridation Si 3 N 4 film growth DFT simulation ABSTRACT Nitridation of silicon surface is an important step in GaN or AlN nanostructures growth process which de- termines quality of fabricated devices. In this work modeling of gas-surface reaction of the Si(111) surface nitridation was performed using density functional theory calculations. We show that interface structure cor- responding to first stoichiometric Si 3 N 4 monolayer may be generated in a great number of different ways by means of vacancy-assisted mechanism. The nearly continuum distribution of total energies may be associated with such structures formed after exothermic reaction with considerable energy gain. Nevertheless founded global minimum corresponds to abrupt interface and crystalline-like Si 3 N 4 monolayer structure. Suggested mechanism of silicon nitride film growth is based on the calculated energy barriers for diffusion of volatile species such as N, N 2 , SiN and SiN 2 which are building blocks for the growth of Si 3 N 4 film. At first stage atomic nitrogen diffusion from vacuum to substrate occurs. Then silicon vacancies in substrate and volatile SiN radicals are formed. The back diffusion of SiN from substrate to Si 3 N 4 -vacuum side is the main mechanism responsible for silicon nitride film growth. 1. Introduction III-nitride based optoelectronic devices require the use of the Ga or/ and Al nitride films or nanowires (NWs). The growth of such structures had been a difficult problem unless suitable substrates and growth methods were founded. Specifically, silicon (111) substrates were as- certain as the most appropriate ones for several reasons including low cost and availability of large wafer sizes. However, there are some problems related to using of such substrates. In particular, early stages of growth show an emergence of a buffer silicon nitride layer between the substrate and film as soon as the nitrogen source is switched on before the GaN or AlN films grow [1–3]. This buffer layer was shown to be unavoidable [4] unless the substrate was initially protected by Al prelayer and was found to be about 2 nm thick [5]. Later on it was understood that for growing of perfect GaN or AlN structures on Si(111) it is worth to obtain firstly the silicon nitride buffer layer [6] through the nitridation of the Si- surface. For example, structural quality of GaN films grown on ultrathin Si x N y intermediate buffer layer were strongly dependent on the structural perfection of such layer [7]. The main problems associated with this metod are low growth rate of the buffer and a strong dependence of its properties on a great number of technological parameters, which might have a significant effect on the final structures. Therefore mechanisms and quality of the Si(111) substrates nitridation have been in the focus of many further studies both for academical and technological reasons (see e.g. [4,8]). As a result of these investigations it was found that the silicon surface nitridation reaction is self limited [9] and that the thickness of the nitrided film is usually in the range of 2÷4 nm. Secondly, the final result of the nitridation is nearly independent on the nitrogen species used for this purpose. For example, application of N 2 , NH 3 or NO mo- lecules had a similar effect [10]. However, the presence of atomic N in the plasma strongly speeded up the process of nitridation [11]. There is a number of theoretical studies discussing structures of the Si 3 N 4 /Si(111) interface created by reaction of nitrogen ions with the Si (111) surface [12,13,14,36,15]. In these papers only idealized interface models were considered with abrupt Si 3 N 4 /Si(111) interface when crystalline Si 3 N 4 film forms interface with crystalline silicon substrate. We suppose that such structure may be realized in practice only when both Si and N atoms are present in plasma over perfect silicon substrate and silicon atoms for Si 3 N 4 film growth are taken from plasma. However in the present work we are interested in GaN growth technology in which external source of Si atoms is not used, so silicon https://doi.org/10.1016/j.apsusc.2019.03.239 Received 18 November 2018; Received in revised form 27 February 2019; Accepted 22 March 2019 ⁎ Corresponding author. E-mail address: petrenkotl@isp.kiev.ua (T.L. Petrenko). Applied Surface Science 483 (2019) 302–312 Available online 27 March 2019 0169-4332/ © 2019 Elsevier B.V. All rights reserved. T