A lattice gas model of II-VI(001) semiconductor surfaces

We introduce an anisotropic two-dimensional lattice gas model of metal-terminated II-VI(001) semiconductor surfaces. Important properties of this class of materials are represented by effective NN and NNN interactions, which results in the competition of two vacancy structures on the surface. We demonstrate that the experimentally observed transition from the dominant c(2 x 2) ordering of the CdTe(001) surface to a local (2 x 1) arrangement of Cd atoms can be explained as a phase transition in thermal equilibrium. The model is studied by means of transfer-matrix and Monte Carlo techniques. The analysis shows that the small energy difference of the competing reconstructions determines to a large extent the nature of the different phases. Possible implications for further experimental research are discussed.