THE EFFECTS OF NONEQUILIBRIUM CHARGE-DISTRIBUTION IN SCANNING TUNNELING SPECTROSCOPY OF SEMICONDUCTORS

Results are presented from a low-temperature scanning tunneling micros copy (STM) investigation of III-V semiconductor surfaces cleaved in si tu along a (110) plane. The STM topographic images reveal the presence of surface charge structures. The possibility of their observation de pends on the charge state of the apex of the STM tip. Peaks are also o bserved in the local tunneling conductivity spectra. The energy positi on of these peaks and the energy position of the edges of the band gap change with distance from the defect. A theoretical model is proposed which demonstrates that the experimental scanning tunneling spectrosc opy (STS) data can be explained by effects due to a nonequilibrium ele ctron distribution in the contact area, which gives rise to localized charges. In this model the on-site Coulomb repulsion of localized char ges and their interaction with semiconductor electrons are treated sel f-consistently. (C) 1998 American Institute of Physics. [S0021-3640(98 )01016-0].