AVS 47th International Symposium
    Processing at the Nanoscale/NANO 6 Friday Sessions
       Session NS+NANO6+MC-FrM

Paper NS+NANO6+MC-FrM8
Atomically-resolved Observation of Single Surface States and Trapped Electrons at Semiconductor Surfaces using Photovoltage Imaging with STM

Friday, October 6, 2000, 10:40 am, Room 302

Session: Nanoscale Spectroscopy
Presenter: G. Haase, Weizmann Institute, Israel
Authors: S. Aloni, Weizmann Institute, Israel
I. Nevo, Weizmann Institute, Israel
G. Haase, Weizmann Institute, Israel
Correspondent: Click to Email
Atomically-resolved, super- and sub-band-gap photon surface photovoltage (SPV) imaging was used to study surface states and a trapped exciton at semiconductor surfaces. Super-band-gap radiation that flattens the electronic bands gives rise to SPV that reflects the local band bending in the dark. On the other hand, a sub-band-gap photon can excite a localized electron in a surface state into the conduction band, and produce an SPV that reflects the new charge distribution. By studying the effect of the tip on the local band bending, we can learn about the nature of a single localized surface state on an otherwise surface-state-free surface. It turns out that a single adsorbate or a single atom-size defect, can sometimes screen efficiently a strong external electric field. When a filled deep surface state, such as As-vacancy defect on the surface-state-free GaAs(110) surface, was excited by 1064 nm (sub-band-gap) illumination, a trapped electron state was imaged: It's induced SPV feature had a slight positive value at a radius of ~20 AA, and a negative portion 5-50 AA further away, as expected for a localized positive charge with a wide (bias-dependent radius of 25-70 AA) electron-density distribution around it. An observed six-point star shape of the SPV feature is explained by the contribution of the surface atoms to the potential well shape.