Optimized chemical cleaning procedure for enhancing photoemission from GaAs photocathode

Abstract

To obtain cleaner GaAs photocathode surface, various wet chemical cleaning methods to remove the oxides and carbon contaminations from the surface of GaAs photocathode are investigated, and an improved chemical etching method is presented to further enhance the cathode photoemission performance. By means of X-ray photoelectron spectroscopy analysis, characteristics of these methods are summarized. HF solution can effectively reduce surface oxides, but it does not effectively act on the absorbed carbon contaminations. The mixed solution of HCl and isopropanol scores well in removing carbon contaminations, but the ability of removing oxides is relatively weaker. The mixed solution of HCl and deionized water right after the mixed solution of H2SO4, H2O2 and deionized water is unfavorable to reduce Ga oxides. The improved chemical etching method, which uses HF solution followed by the mixture of HCl and isopropanol has more advantages in removing oxides and carbon contaminations at the same time. Moreover, a hydrophobic surface is obtained by using the improved method, which also plays a role in the contaminations removal. The quantum efficiencies of GaAs photocathode undergoing various wet chemical cleaning procedures are compared after subsequent heat treatment and activation. The results show that the chemical treatment of HF solution followed by the mixture of HCl and isopropanol can help GaAs photocathode obtain higher activated photocurrent and quantum efficiency.