Effect of UV/ozone treatment in chemical cleaning procedure on photoemission performance of GaAs and GaN photocathodes

Abstract

To obtain a cleaner surface and enhance the photoemission performance of III-V photocathode, a comparative study of cleaning procedure using acidic solutions and UV/Ozone treatment, respectively, is investigated in GaAs and GaN photocathodes. The subsequent heat treatment and activation are carried out and the quantum efficiencies of GaAs and GaN photocathodes taking the different cleaning methods are compared. The results show that the quantum efficiency of GaN photocathodes with UV/Ozone treatment can be higher than using acidic solutions, while for GaAs photocathodes, the results are completely different. By using X-ray photoelectron spectroscopy analysis, we summarize the characteristics of these treatments, trying to find the function mechanism. The XPS spectra show that UV/Ozone treatment can effectively restrain carbon contaminations of these photocathodes. But the strong oxidizing properties of UV/Ozone treatment on GaAs surface leads to the generation of more oxides, and even the high-temperature heating cannot remove them. Conversely, no additional oxidation of GaN by UV/Ozone treatment is observed, and the reduced carbon contamination results in an increase of quantum efficiency of the GaN photocathode.