Modelling sublimation and atomic layer epitaxy in the presence of competing surface reconstructions

Abstract

We present a solid-on-solid model of a binary AB compound, where atoms of type A in the topmost layer interact via anisotropic interactions different from those inside the bulk. Depending on temperature and particle flux, this model displays surface reconstructions similar to those of (001) surfaces of II-VI semiconductors. We show, that our model qualitatively reproduces many of the characteristic features of these materials which have been observed during sublimation and atomic layer epitaxy. We predict some previously unknown effects which might be observed experimentally. Keywords: Monte Carlo simulations, Surface relaxation and reconstruction, Models of nonequilibrium phenomena, Evaporation and sublimation, GrowthApart from a few exceptions (eg.[1]), theoretical models of crystal surfaces in nonequilibrium situations have not taken into account the effects of surface reconstructions, so far. Consequently, a theoretical understanding of the interplay of this phenomenon with the dynamics of growing or sublimating surfaces has not yet been achieved. In this paper we will address this important question in the context of a compound material that displays a competition of different vacancy structures in the terminating layer.Within the last years, there have been intensive experimental studies concerning the surfaces of II-VI semiconductors, see eg. [2,3] for an overview. These studies have revealed the existence of a fairly small number of surface reconstructions, which makes them promising candidates for a theoretical modelling. In the following, we will refer mostly to experimental results for CdTe(001) [2][3][4][5][6][7][8][9]. Under vacuum conditions, the CdTe(001) surface is metal terminated. The Cd atoms arrange in a vacancy structure, where half of the potential Cd sites are empty. At low temperatures, a c(2 × 2) reconstruction is observed, in which Cd atoms arrange in a checkerboard like configuration. Often a contribution of (2 × 1) arrangement in rows along the (110) direction is observed. At a temperature of ≈ 300 0 C, a reordering occurs, above which a (2 × 1) ordering dominates on a sublimating surface. An additional Cd flux stabilizes the c(2 × 2) ordering even at high temperatures. Under a Te flux, the surface is Te-terminated, with a (2 × 1) reconstruction. At small Te fluxes, the Te-coverage is 1, at low temperatures and high Te fluxes a higher coverage of 1.5 is observed [3,5,6,8]. In this Letter, we present a 2+1-dimensional solid-on-solid model of a binary compound material to get insight into the following problems: (1) Is the claim [6] of an effective thermal equilibrium of the surface layer justified under the non-equilibrium conditions of sublimation? (2) What is the effect of an external particle flux on the surface reconstruction? (3) How do reconstructions influence techniques of crystal growth like atomic layer epitaxy (ALE)?In the terminating layer of a CdTe(001) surface, the potential Cd sites form a regular square lattice, where the simultaneous occupation of nearest neighbour (NN...

Kinetic model of II-VI(001) semiconductor surfaces: Growth rates in atomic layer epitaxy

“…This re-arrangement of the surface is observed under step flow sublimation, as demonstrated earlier in Refs. 16,17, and a semi-quantitative agreement with experimental data can be achieved.…”

“…Chemical bonds and the influence of the underlying crystal were accounted for by effective pairwise anisotropic interactions. Sublimation and ALE growth have been studied in the framework of a simple cubic model, 17 which accounted only for the most essential features of CdTe. The correct zinc-blende lattice was first considered in Ref.…”

Flat (001) surfaces of II–VI semiconductors: a lattice gas model

“…At the temperature of the c(2 × 2) Cd -(2 × 1) Cd transition, sublimation plays an important role. However, in a previous publication [23] we have shown that the basic features of a simplified version of our model which neglects Te dimerization [12] are preserved under the conditions of step flow sublimation. This is the dominant sublimation mechanism for CdTe (001) [24].…”

Density‐functional study on the migration of Cd and Te adsorbates on the (001) surface of CdTe

“…Biehl et al introduced the anisotropic two‐dimensional lattice gas model for investigations of the metal‐terminated II–VI (001) semiconductor surfaces 17–20. This model reproduces many of the characteristic features of these materials.…”