title: Direct evidence for shallow acceptor states with nonspherical symmetry in GaAs.
abstract: We investigate the energy and symmetry of Zn and Be dopant-induced acceptor states in GaAs using cross-sectional scanning tunnelling microscopy (STM) and spectroscopy at low temperatures. The ground and first excited states are found to have a nonspherical symmetry. In particular, the first excited acceptor state has a T(d) symmetry. Its major contribution to the STM empty-state images allows us to explain the puzzling triangular shaped contrast observed in the empty-state STM images of acceptor impurities in III-V semiconductors.
authors.affiliation: Institut d'Electronique, de Microélectronique et de Nanotechnologie, IEMN, (CNRS, UMR 8520), Département ISEN, 41 bd Vauban, 59046 Lille Cedex, France.
authors.forename: G
authors.initials: G
authors.lastname: Mahieu
authors.forename: B
authors.initials: B
authors.lastname: Grandidier
authors.forename: D
authors.initials: D
authors.lastname: Deresmes
authors.forename: J P
authors.initials: JP
authors.lastname: Nys
authors.forename: D
authors.initials: D
authors.lastname: Stiévenard
authors.forename: Ph
authors.initials: P
authors.lastname: Ebert