Remotely-Doped Sb Quantum-Well Structures

Antimony (Sb) has topological surface states, but its bulk is semimetallic. Our goal is to study the transport properties of the topological states by suppressing the bulk conductivity through quantum confinement and enhancing the surface conductivity through remote n-type doping. A series of Sb quantum-well (QW) structures were grown by molecular beam epitaxy using GaSb barrier layers and GaSb or GaAs substrates. Transport measurements on undoped Sb QWs, 0.7 to 6 nm thick, show a suppression of the bulk conduction. Interpretation of Hall-effect measurements is complicated by the presence of both electrons and holes. We have begun experiments to populate the topological electron states by n-doping the GaSb barrier with Te atoms. We observed that the Hall coefficient at low temperature decreases with increasing distance between the doped layer and the QW. This indicates that the QW is populated by electrons from the dopants in the barrier layer, but parallel conduction by holes is still significant. We will report on the next series of structures with Al(x)Ga(1-x)Sb barriers and optimized doping densities.