Structural and electronic properties of Bi/GaAs(110)

Abstract

Ordered Bi overlayers on GaAs(110) were investigated with scanning tunneling microscopy (STM), STM spectroscopy, low-energy electron diffraction (LEED) studies, and with angle-integrated and angle-resolved photoemission spectroscopies. Two-dimensional (2D) layer growth occurs to ∼1 monolayer (ML), thereafter three-dimensional (3D) growth dominates. A Bi phase pseudomorphic with the GaAs is observed to ∼10 ML. Interdiffusion or chemical reactions between the components were not detected. STM images for coverages of 0.5 and 1 ML reveal the Bi structure to consist of chains of atoms aligned above and in between the Ga–As zigzag surface chains. Additional evidence for dual bonding sites of the Bi suggests that the Bi chains exhibit a zigzag structure similar to the Sb/GaAs system. Near 1 ML the Bi chains are interrupted by a periodic array of dislocations, ∼25 Å apart, that consist of missing Bi atoms. STM spectroscopy reveals that the Bi ML is semiconductorlike with a 0.7-eV band gap, and that the dislocations generate a band of empty, acceptorlike states within this gap. Band bending measurements indicate that the position of the Fermi level on n-type GaAs is determined by these acceptor states. Gap states were also associated with Bi terrace edges for coverages <1 ML. The position of the Fermi level for Bi on p-type GaAs is determined by the top of the Bi valence band, which overlaps that of GaAs by 0.4 eV. The dispersion of this band and another lower Bi band were measured using angle resolved photoemission spectroscopy.