Intrinsic Surface States in Semiconductors. I. Diamond-Type Crystals

Intrinsic surface states on clean and perfect surfaces of semiconductors are investigated. Calculations are made for (111) and (100) surfaces of diamond-type crystals, C, Si, Ge and α-Sn, with a tight-binding approximation including interactions up to nearest-neighbor distances. Second-nearest-neighbor approximation is also examined for Si and Ge. Spin-orbit coupling is wholly neglected. For the (111) orientation, two types of surfaces are considered: one intersects one bond per surface atom (denoted as (111)–1) and the other dose three bonds (denoted as (111)–3). It is shown that the surface band structures of the diamond-type crystals are correlated with the shape of the conduction bands and the specific surface energy of the (111)–1 surface is lower than those of the (111)–3 and (100) surfaces. Surface reconstruction is not considered in the calculation but its close relationship with the surface states is discussed.