The bulk photovoltaic effect describes the generation of photocurrents and photovoltages in bulk materials lacking a center of symmetry. Its principal mechanism is “shift current,” a nonlinear-optical, inherently quantum mechanical process. While most attention has been devoted to its prospects as a means of solar energy capture, shift current bulk photovoltaic effect possesses a number of distinguishing features that make it well-suited to sensing and switching applications: photovoltages substantially exceeding the material’s band gap, response amplitudes and directions that can depend on both photon energy and polarization, and response that occurs on ultrafast timescales.
"The bulk photovoltaic effect as a novel mechanism for sensing devices and applications", Proc. SPIE 9835, Ultrafast Bandgap Photonics, 98350P (13 May 2016); doi: 10.1117/12.2225103; https://doi.org/10.1117/12.2225103