Theory of exciton effects in semiconductor surface spectroscopy

Electronic excited states at the 〈001〉 and 〈111〉 surfaces of a simple cubic solid are investigated, with inclusion of a contact electron–core hole interaction. Contributions of bulk and surface bands to bound and resonant excitons are derived without approximations. The resulting spectrum dramatically depends on the nature and energy of empty surface states. A large increase of the exciton binding energy near the surface is obtained in some situations, while in others binding is suppressed altogether in the first few planes, and a ’’dead layer’’ results. Limiting cases relevant to the discussion of recent observations of surface excitons in semiconductors and insulators are identified.