Electron escape probability in high-efficiency photocathodes measured by reverse-injection photovoltage

The characterization of electron transfer through the emitting surface is of crucial importance for optimizing existing and developing new photocathodes. Here we propose and develop a method for the direct determination of the electron escape probability in high-efficiency semiconductor photocathodes. The proposed method is based on the variations in the surface photovoltage upon the injection of emitted photoelectrons back into a photocathode (``reverse injection"), which is induced by the polarity reversal of the external electric field. We demonstrate the method on \textit{p}-GaN(Cs,O) photocathodes with negative effective electron affinity by measuring the evolution of photoemission quantum efficiency upon the reverse injection of emitted electrons.