AN ELECTROREFLECTANCE STUDY OF N-TYPE AND P-TYPE GALLIUM-ARSENIDE IN AQUEOUS-ELECTROLYTES

Electroreflectance was used to study the variation of the space-charge voltage with applied potential for n- and p-type GaAs in a series of aqueous electrolytes. The results were modeled by an intermediate-field Franz-Keldysh theory that included the electric-field variation within the depletion layer. Comparison of the theoretical and experimental spectra effectively allowed the space-charge voltage to be measured at each applied potential. In all cases the space-charge voltage was found to vary much more slowly than the applied potential on approach to the expected flatband potential and it was possible to characterize in some detail the changes in the ac and dc potential distribution that occurred. In addition, the rapid Fermi-level pinning of p-type GaAs in 0.1 mol KOH was found to be passivated by small concentrations of polysulfide ions. Spectra that were measured under either acidic or alkaline conditions showed quite large changes in line shape with applied potential, as expected. However, for n-type GaAs in pH-5 0.1 mol Na2SO4, little line-shape variation occurs and the space-charge voltage is shown to be fixed close to 0.3 V over a large range of applied potential.