Modeling (001) surfaces of II–VI semiconductors

Abstract

First, we present a two-dimensional lattice gas model with anisotropic interactions which explains the experimentally observed transition from a dominant c(2 × 2) ordering of the CdTe(001) surface to a local (2 × 1) arrangement of the Cd atoms as an equilibrium phase transition. Its analysis by means of transfer-matrix and Monte Carlo techniques shows that the small energy difference of the competing reconstructions determines to a large extent the nature of the different phases. Then, this lattice gas is extended to a model of a three-dimensional crystal which qualitatively reproduces many of the characteristic features of CdTe which have been observed during sublimation and atomic layer epitaxy.Within the last years, potential applications of electronic devices based on II-VI semiconductors have inspired basic research concerning for instance the surface reconstructions of these materials. For CdTe, a fairly complete qualitative phase diagram of (001) surfaces has been obtained [1]. An understanding of the interplay of these reconstructions with techniques like molecular beam epitaxy (MBE) or atomic layer epitaxy (ALE) is desirable both for technological applications and for the theory of crystal growth. From the theoretical point of view, the case of CdTe is especially interesting, since it exhibits a phase transition which involves competing reconstructions at typical MBE growth temperatures. While there have been a few models of MBE, especially for GaAs which take into account the effects of surface reconstructions (e.g. [2]), phase transitions between different reconstructions have not been considered in growth

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.…”

“…In simpler versions of the model it was possible to reproduce the temperature dependence of the surface reconstruction as well as macroscopic sublimation rates on a semiquantitative level. 16 The larger number of parameters in the current extension, however, requires further input from experiment. Moreover, we hope to obtain reliable estimates of microscopic activation barriers from first principle quantum chemical calculations as are already available for III-VI semiconductors.…”

“…The correct zinc-blende lattice was first considered in Ref. 16, but here we extend the model significantly by taking into account the formation of Te-dimers at the surface. More importantly, we will consider weakly bound excess Te, which provides a reservoir of highly mobile atoms.…”