Speaker
Description
We report on our recent advancements in development of a fully automated growth procedure for alkali antimonide photocathodes. Our goal is to create a capability that allows fabrication of uniform fully stoichiometric alkali antimonide films of any given thickness at sufficiently low substrate temperatures, where the compounds are stable. We show that co-evaporation procedure at low substrate temperatures requires delivery of reactants to the growth surface in precise proportions; otherwise, non-stoichiometric material is produced. For the purposes of process control, we introduce a thickness-independent parameter that reflects photocathode’s quality (quality parameter) and can be used to monitor the growth process and provide feedback for flux control algorithms. We demonstrate a technique that allows quasi-continuous acquisition of spectral response characteristics during the growth, which renders the quality parameter. We provide experimental data that indicates feasibility of on-the-fly flux adjustments that are needed to quickly achieve and then maintain the optimum stoichiometry of the film during the growth cycle. We discuss the choice of the flux control algorithms with the emphasis on adaptive control and simultaneous optimization of multiple parameters.
