Polarity-dependent emission and conversion characteristics of GaN-based thermionic cathodes

We observed the polarity-dependent thermionic emission and conversion characteristics of Si-doped n-type GaN-based cathodes with Cs adsorbed on their surfaces. Emission current from the surface of the GaN sample with N -polarity was markedly higher than that with Ga-polarity. We consider that the N-polarity enhanced the surface potential lowering for electrons due to the Cs atom adsorption. These results indicate that, from the viewpoint of a thermionic converter, the electromotive force for emission was higher for N -polarity compared with Ga-polarity.