INTERPRETATION AND USE OF MOTT-SCHOTTKY PLOTS AT THE SEMICONDUCTOR ELECTROLYTE INTERFACE/

The Poisson Boltzmann equation is solved for a semiconductor without m aking the usual assumption of no majority carriers in the depletion la yer. The capacative behaviour of the semiconductor is combined with th at of the Helmholtz layer to provide a complete description of the pot ential distribution in the electrolyte and in the semiconductor for al l applied potentials including accumulation, the flat band transition and depletion. Calculations show that good linear Mott-Schottky plots are obtained in the depletion region even when 90% of the potential is across the Helmholtz layer. A procedure is described which uses the c urvature of the Mott-Schottky plot in the region of the flat band pote ntial to determine the ratio of the semiconductor capacitance to that of the Helmholtz layer. This allows one to determine experimentally th e amount of band bending in any system. The procedure is illustrated w ith data for tin-doped indium oxide. Reasonable values are obtained fo r the doping density, the Helmholtz capacitance and the true hat band potential.