High Photostrictive Strain Rate in Ferroelectric AlScN Thin Films

Photostriction refers to non-thermal strain in materials induced by light, such as through opto-electro-mechanical coupling involving the bulk photovoltaic effect (BPVE) and the converse piezoelectric effect in a ferroelectric material. Conventional ferroelectric photostrictive responses are extremely slow, with strain rates below 10^{- 3} s^-1 due to the long timescale of BPVE, limiting their use in high-frequency or signal transmission applications. This work demonstrates a significantly enhanced photostrictive strain rate of 3.6 s^-1 in scandium aluminium nitride (Al_0.58Sc_0.42N) thin films under modulated continuous light excitation. The light-induced strain amplitude is equivalent to that of electric-field induced strain with 2 V applied across the film, underscoring the significant and competitive opto-mechanical coupling. This fast response is attributed to nanoscale columnar domains that reduce the electric time delay and charge carrier drift distances, enabling rapid strain generation. The demonstrated fast photostriction provides a unique pathway for light-driven actuation and acoustic wave excitation without requiring electrical wiring, electrodes or electric poling, thus, opening opportunities for developing acoustic micro-actuators and novel optomechanical systems operating in a non-contact mode.