INTERFACE-STATE DENSITY AT SIO2 GAAS ASSESSED BY DIRECT MEASUREMENT OF SURFACE BAND BENDING/

Electroreflectance is applied to study the interface properties of met al/SiO2/GaAs structures. From a bias-voltage dependence of surface pot ential, which was evaluated from the measured surface field in i/n(+)- GaAs structures, energy distributions of interface-state density were determined based on the modulation spectroscopy technique. Upon biasin g toward inversion, a strong: pinning of surface Fermi level occurred at around 0.88 eV below the conduction-band minimum. This pinning, thu s, is concluded to be due to a large number of interface states, and n ot due to an actual hole inversion. The method is free from numerical ambiguities encountered in capacitance-based techniques, in which the energy reference for surface Fermi level is model dependent, and thus, is a suitable tool for studying insulator/semiconductor interfaces, e ven having a large number of interface traps. (C) 1996 American Instit ute of Physics.