Difference in the photocurrent of semiconductor photodiodes depending on the polarity of current measurement through a contribution from the photoemission current

摘要

When using semiconductor photodiodes in the VUV, photoelectrons emitted from the photodiode surface form an additional current circuit when electrons reach a vacuum chamber wall surrounding the photodiode. In the case where the rear electrode of the photodiode is grounded, and hence the sensing terminal of an electrometer is connected to the front electrode, the electrometer measures the superimposed current, that is, the photocurrent internally generated in the p-n junction plus the photoemission current. Experiments done for diffusion-type silicon photodiodes and Schottky-type GaAsP photodiodes in the wavelength range from 50 nm to 200 nm show that the photoemission contribution has peaks of about 10% and 25%, respectively, of the internal photocurrent at around 100 nm for both without an extraction voltage. Therefore, for precise measurements of semiconductor photodiode photocurrents, the sensing terminal of an electrometer should be connected to the rear electrode of a photodiode to avoid any contribution from the photoemission current.