Shift current: A quantum-mechanical photovoltaic effect in noncentrosymmetric crystals

Abstract

Materials lacking inversion symmetry generate photocurrent without an external electric field. Although this phenomenon was found more than 50 years ago, its mechanism has remained controversial. Recently, its principal mechanism is theoretically suggested to be the shift current, which is a purely quantum-mechanical photocurrent driven by the geometric phase of the electron wave function. We have experimentally demonstrated the prominent features of the shift current, such as the robustness against carrier scattering, a high photovoltage far exceeding the bandgap, and an ultrafast response to pulsed light. These features are a great advantage for optoelectronic applications including solar cells and high-speed photo-detectors.