The photocurrent may be enhanced by internal gain caused by interaction among ions and photons under the influence of applied fields, such as occurs in an avalanche photodiode (APD).
[1] The setup of the technique involves having a semiconductor contacted with electrodes allowing for application of an electric bias, while at the same time a tunable light source incident with a given specific wavelength (energy) and power, usually pulsed by a mechanical chopper.
[2][3] The quantity measured is the electrical response of the circuit, coupled with the spectrograph obtained by varying the incident light energy by a monochromator.
The measurements give information related to the band gap of the semiconductor, allowing for identification of various charge transitions like exciton and trion energies.
This is highly relevant for studying semiconductor nanostructures like quantum wells,[4] and other nanomaterials like transition metal dichalcogenide monolayers.