Surface Fermi-level changes in n-type GaAs determined from Hall-effect measurements

Changes in the surface Fermi-level position in n-type epitaxial GaAs samples are determined by Hall-effect measurements of the corresponding changes in the sheet concentrations and theoretical calculations of the surface depletion thickness. The changes are induced and reversed repeatedly by alternating wet chemical treatments in hydrogen peroxide and ammonium hydroxide. This is the first known use of hydrogen peroxide to restore the surface Fermi level to near its starting value and demonstrate the repeated variation of the surface Fermi level by ammonium hydroxide. The results agree with the predictions of the advanced unified defect model and with published reports of increased band bending on n-type material, rather than with conflicting reports of decreased band bending. The results also indicate that problems may exist with other techniques used to measure surface- potential changes.