MBE Growth of Custom-Designed III-V Semiconductor Microstructures Scaled to the Physical Limit: Ultrathin-Layer Superlattices and Monolayer Doping

Abstract

Molecular beam epitaxy (MBE) of custom-designed microstructures has reached a status where monolayer dimensions in artificially layered semi­conductors are being routinely controlled to form a new clls of materials with accurately tailored electrical and optical properties^1,2. The unique capabilities of molecular beam epitaxy in terms of spatially resolved ma­terials synthesis has stimulated the inspiration of device engineers to design a whole new generation of electronic and photonic devices based on the concept of band gap engineering^3,4. This concept, also called wavefunc­tion or density-of-states engineering^5,6, respectively, relies on the ar­bitrary modulation of band-edge potentials in semiconductors through the abrupt change of composition (e.g. GaAs/AlAs, GaSb/InAs, Si/Ge, etc.) or of dopant concentration. The microscopic structuring or engineering of se­miconducting solids to within atomic dimensions is thus achieved by the incorporation of interfaces (consisting of abrupt homo- or heterojunctions) into a crystal in well-defined geometrical and spatial arrangements. The electrical and optical properties are then defined locally, and phenomena related to extremely small dimensions (“quantum size effects”) become more important than the actual chemical properties of the materials involved.