Effects of H⁺ ion bombardment on GaAs photocathode surface with Cs-O and Cs-F activation layers

To characterize the degree of damage to the GaAs photocathode surface caused by H+ ion back bombardment in the electron-bombarded complementary metal-oxide-semiconductor (EBCMOS), Stopping Range of Ions in Matter software based on the Monte Carlo method was used to investigate the effect of H+ ions with different incident energies on the surface of Cs-O (Cs-F) activated GaAs photocathode. During the simulations, different Cs/O (Cs/F) ratios ranging from 1:1 to 4:1 were considered. The sputtering rates, backscattering electrons, and longitudinal and lateral displacements along with vacancies/ions were investigated. According to the analysis of sputtering rates and vacancies, the optimal Cs/O ratio and Cs/F ratio are 3:1 and 4:1, respectively. With the increase in the incident energy, the backscattering rates decrease, the peak value of the H+ ion distribution decreases, while the corresponding peak position increases, and the peak value of the vacancy distribution increases first and then decreases, while the corresponding peak position increases. In addition, the projected ranges, and lateral and longitudinal displacements increase with the increase in incident energies, while the projected ranges may far exceed the straggle lengths and make the ion trajectory become more and more concentrated in the high incident energy region. This work helps to understand the degeneration mechanism of the GaAs photocathode operating in EBCMOS.