Effect of formation on the quantum efficiency of cesium telluride thin-film photocathode

The photocathode for practical usage should be guaranteed to keep high performance level stable in long time and reproducibility. The quantum efficiency of a cesium telluride thin film photocathode changes in accordance to deposition conditions of cesium telluride. Conditions here include: the thickness of tellurium, the quantity of deposited cesium, passage of time from production of thin film, and a substrate condition to deposition. In this study, we produced thin films different deposition conditions of tellurium and cesium, and investigated about the spectral properties. We produced thin films by two cesium deposition methods: (1) suspending cesium evaporation at the time reaching the maximum photocurrent, and (2) wait for recovering the photocurrent after the excess cesium deposition. The quantum efficiency measurements were carried out in tellurium thickness range of 5-15nm. The results revealed that the quantum efficiencies at the 5eV energy region were high about 20% and fluctuations in quantum efficiencies were within 10-20% under the present tellurium and cesium deposition conditions. Below 4eV, the quantum efficiencies were very low and we observed differences of more than 10 times among these deposition conditions. (author)