First-principles study of the atomic reconstructions of ZnSe(100) surfaces

First-principles studies of the atomic reconstructions of CdSe (001) and (111) surfaces

We have performed the first-principles total-energy calculations to investigate (2 × 1), (1 × 2), (2 × 2), (4 × 2) and (2 × 4) reconstructions of Cd- and Se-terminated CdSe(001) and (111) surfaces as a function of the surface stoichiometry and the Cd chemical potential. We find that there exist Cd dimers on the (001) surface and Se tetramers on the (111) surface. Comparing surface formation energies as a function of the Cd chemical potential μ(Cd), we find the Cd-vacancy and Se-vacancy (2 × 2) structures to be energetically favorable for the Cd-terminated (001) surface at high μ(Cd) and Se-terminated (001) surface at low μ(Cd), respectively. In contrast, an Se-tetramer (2 × 4) structure is more favorable than the vacancy structure for the Se-terminated CdSe(111) surface almost in the whole region of allowed μ(Cd).

Chemical surface analysis by Raman spectroscopy utilizing dimer vibrations

We report on the investigation of reconstructed semiconductor surfaces by Raman spectroscopy from dimer vibrations. Localized modes of Te dimers on the (100) surface of the zinc blende II-VI semiconductor BeTe allow the analysis of Te- and Be-rich surface structures, as well as oxidation effects. The Te-rich surface exhibits one dimer-vibration mode at 165 cm(-1), while two modes appear at the Be-rich surface (157 and 188 cm(-1)). The mode assignment as dimer vibrations is underscored by their symmetry properties and by frozen phonon calculations, yielding mode frequencies and eigenvectors. This approach opens up a new field of surface chemistry analysis by dimer-vibration spectroscopy.