Comparison of first and second annealing GaN photocathode.

We anneal GaN samples in ultra high vacuum system for two times at the same temperature of 710 °C, and activate the sample after each heating by Cs/O. The vacuum level, residual gas, QE, and photocurrents are compared. We find, for the 1st annealing vacuum level line has a shape of “W”, but the 2nd looks like “V”. The residual gases include H2, H2O, N2, and CO2 mainly. Nothing else has been detected significantly. For the 1st annealing, there are two stages the residual gases come out quickly, but nothing comes out until the maximum temperature during the 2nd annealing. Before activation, the photo-current after 2nd heating is higher than the 1st, which shows the stability of GaN. No obvious difference of QE has been found between the two times annealing, and more researches will be done on this topic. [ABSTRACT FROM PUBLISHER]