Surface-state mediated optical actuation of GaAs microcantilevers

We demonstrate optical actuation of n-GaAs microcantilevers using homogeneous, nanowatt-level LED illumination. Intensity-modulated light induces a surface photo-voltage that changes the depletion layer at the GaAs surface, generating a time-dependent piezoelectric stress that drives flexural motion at mechanical resonance. Resonant actuation is achieved without focused beams, optical cavities, or complex heterostructures. Orientation-dependent static deflection, bias-polarity-dependent phase response, and negligible resonance-frequency shifts under illumination distinguish this mechanism from photothermal, electrostatic, and radiation-pressure effects. These results identify surface-state-mediated piezoelectric coupling as an efficient optomechanical interaction in GaAs, enabling low-power optical control of micro- and nanomechanical resonators.