The imprint of the changing surface concentration of minority carriers in photocurrent transients is marginalized in “switch off” transients as compared to “switch on” transients. When the surface level is situated close to either one of the band edges, it is shown that in principle it must be possible to obtain the energy of the surface level from “switch off” transients. The time constants for the “switch on” and “switch off” cases behave differently with potential. While in “switch off”, transient plots, the magnitude of the slope decreases monotonically with increasing band bending potentials; for the “switch on” however, though it decreases and is identical to “switch off” initially, beyond a certain increase in potential the magnitude of the slope shows an increase.
Ramakrishna, S., Rangarajan, S. K., & Sesha Shankar, R. (1991). A note on transient photocurrents at semiconductor electrodes. J. Electroanal. Chem., 308, 39. https://doi.org/10.1016/0022-0728(91)85057-V