Cleaved {110} Surfaces of III–V and II–VI Compound Semiconductors

Abstract

Compound semiconductors, which crystallize in the cubic zincblende structure, cleave along {110} planes. Such planes contain the same number of anions and cations per unit area and are thus intrinsically neutral. With {110} surfaces of compound semiconductors no reconstructions are observed but the surface atoms relax from the positions expected for a bulklike termination such that the cation-anion zigzag chains become tilted with the anions being raised. As a result of this relaxation, the total valence charge remains the same around surface and bulk atoms. The dangling-bond surface states are lower in energy at the surface anions than at the surface cations. The band-structure term of the total energy is thus lowered with respect to a bulklike termination when the dangling bonds are completely occupied at the anions but empty at the cations. The surface relaxation indeed shifts the cation dangling-bond band to above the conduction-band minimum. The lowering of the band-structure energy obviously overcompensates the strain energy correlated with the tilting of the cation-anion chains.