Electrowetting on a semiconductor

We report electrowetting on a semiconductor using of a mercury droplet resting on a silicon surface. The effect is demonstrated using commercial n-type and p-type single-crystal (100) silicon wafers of different doping levels. The electrowetting is reversible - the voltage-dependent wetting contact angle variation of the mercury droplet is observed to depend on both the underlying semiconductor doping density and type. The electrowetting behaviour is explained by the voltage-dependent modulation of the space-charge capacitance at the metal-semiconductor junction - current-voltage and capacitance-voltage-frequency measurements indicate this to be the case. A model combining the metal-semiconductor junction capacitance and the Young-Lippmann electrowetting equation agrees well with the observations.