Reconstruction, morphology, and stoichiometry of CdTe(001) and Cd 0.96Zn 0.04Te(001) surfaces

Abstract

The (001) surfaces of commercial, “MBE-ready” CdTe and Cd 0.96Zn 0.04Te substrates were studied by high resolution low energy electron diffraction (SPA-LEED) and Auger electron spectroscopy (AES) with respect to reconstructions, morphologies and stoichiometries. Contrary to the commonly used surface preparation by growth of additional buffer layers, contamination-free and structurally long-range ordered surfaces were achieved by Ar +-sputtering and subsequent annealing at 260–350°C. For CdTe, a mixed c(2 × 2)+(2 × 1) reconstruction with average terraces of up to at least 1000 Å width, separated by double layer steps of (3.3±0.1) A ̊ height, are deduced. The c(2 × 2) domains have a size of ∼65 A ̊ × 300 A ̊ . No facetting was detected. For the Cd 0.96Zn 0.04Te surface, Zn enrichment occurs at temperatures > 300°C, leading to various different surface reconstructions. Depending on annealing conditions and on the number of sputter-annealing cycles performed, (3 × 1), (2 × 1) and c(2 × 2) reconstructions, an increase of the step density and a formation of (011) facets were observed. Different mechanisms for the variation of the surface Zn concentration and of the surface reconstructions are discussed.