IMPEDANCE DIAGRAMS OF SEMICONDUCTOR/OXIDE/ELECTROLYTE (SOE) STRUCTURES TO DERIVE EQUIVALENT R-C COMPONENTS OF THE SEMICONDUCTOR SPACE CHARGE

摘要

The zero current impedance of a silicon substrate in a semi-conductor/oxide/electrolyte (SOE) structure permitted the identification of the contribution of the depletion layer under various bias potentials. Careful measurements using p-Si in a HCl solution within the potential range from 0 to -1 V vs SCE lead to the determination of the corresponding equivalent circuits as a function of the bias potential. Modeling the circuit as a Constant Phase Element (CPE) proved that the imaginary component was a pure capacitor Csc in parallel with a pure resistance RSC. Experimental data showed that these two components undergo a steep variation when the system approaches the silicon flatband potential situation. In this case, a novel fundamental development is presented, assuming that the gradient of potential inside the material is small enough for a simplified treatment based on the linearization of the exponential function. The steep increase in the vicinity of the flatband potential of both the space charge capacitance and conductance was confirmed. It constitutes a useful tool for electrochemical studies to determine the flatband potential and then the band curvature as a function of the sample potential measured vs the SCE reference electrode.