Electronic surface states in GaAs/Ga 1 − xAl xAs superlattice: effect of surface location

Abstract

Two Green function techniques (the direct matching formalism and the interface response theory) are used to investigate the electronic structure of a semi-infinite GaAs/Ga 1 − x Al x As superlattice being in contact with a Ga 1 − y Al y As substrate. The effect of the superlattice termination on the formation of a surface state as well as on the density-of-states distributions is studied in a systematic way by varying the position of the superlattice surface (i.e. substrate/superlattice interface) within a superlattice period. It has been found that the occurrence, the position and the localization properties of surface states are very sensitive to the way the superlattice is terminated—they occur in particular mini-gaps only for some ranges of the outermost layer thickness. When this thickness is close to the value at which surface states merge into the mini-bands, the density-of-states distributions exhibit the most pronounced modifications.