Direct electronic probing of the band-bending profile in semiconductor nanostructures and its impact on the charge transport is a great challenge, since attachment of probing electrodes inevitably modifies the properties of the semiconductor surface. An efficient tool for such investigations may be the terahertz (THz) spectroscopy enabling contactless probing of the pristine surface.
We used time-resolved THz and multi-THz spectroscopies to assess the ultrafast photoconductivity in an array of aligned GaAs nanobars (prepared by MBE growth and e-beam lithography) at 300 and 20 K. These experiments were complemented by time-resolved THz local-probe measurements (THz-SNOM) within a single nanobar and by quantum-based calculations of the THz conductivity of confined electrons.
Our investigations reveal prominent effects of the band bending close to the nanobar surfaces on the picosecond charge carrier dynamics and on the confinement of electrons.