Abstract
The electronic states of Ga-terminated and As-terminated GaAs(100)-(1×1) surfaces and those surfaces with adsorbed O and S are studied by molecular orbital calculation using small cluster models and the discrete variational Xα method. Without adsorption of any foreign atoms, the Ga-terminated surface has 4p-related surface states in the middle of the forbidden band. While, the As-terminated surface has 4p-related surface states in the lower half of the forbidden band. The adsorption sites of chalcogen atoms on Ga- and As-terminated surfaces are determined ab initio by using density functional theory (Gaussian 98). With adsorbed chalcogen atoms, the density of the surface states in the forbidden band of the surface Ga layer markedly decreases, and that of the surface As layer increases. The adsorbates have states in the lower half of the band gap (Ga-terminated surface) or in the valence band (As-terminated surface). The results suggest that a chalcogen adsorbed Ga-terminated and bare As-terminated surface have low surface densities in the upper half of the band gap.
Published Version
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