Surface states in double-well superlattices: symmetric vs asymmetric interwell coupling

Abstract

Electronic level structure and the density of states (DOS) of a semi-infinite superlattice (SL), whose period consists of two GaAs quantum-well layers and two AlxGa1−xAs quantum-barrier layers (the so-called double-well basis), are investigated within an envelope-function approximation. A special attention is paid to surface effects due to the SL termination by a substrate or a cladding layer. In particular, the existence and properties of surface-localized states, as well as a consequent modification of the extended states forming SL minibands, are studied for various terminating conditions, determined by the choice of substrate and the sequence of SL layers approaching the SL surface. The resulting surface electronic structure is shown to be critically dependent on the geometry of the SL basis: For symmetrically (asymmetrically) coupled wells, crossing (anticrossing) of SL minibands occurs, which dramatically influences the energy spectrum of SL surface states as well as the local DOS distributions at the SL end.