Capacitance of semicondoctor-electrolyte junction and its frequency dependence

The frequency dependent capacitance of semiconductor-electrolyte junction and its relationship to the surface roughness of the semiconductor and the ions in the electrolyte are discussed. Due to very low mobility of the ions, the observed capacitance can be dominated by the Helmholtz double-layer of the electrolyte rather than the space charge layer of the semiconductor. The capacitance will also depend on the frequency. This, often observed power-law frequency dependence of capacitance is ascribed to the contribution of constant phase angle impedance. The power-law exponent can easily be related to the fractal dimension if the semiconductor surface can be described by fractal geometry.