Prospect for high brightness III-nitride electron emitter

We describe p-type gallium nitride (GaN) as a candidate for high brightness photocathodes. Experiments utilizing photoemission spectroscopy and quantum yield measurements were performed on GaN films to characterize various cesium and oxygen activations. Quantum efficiencies of 0.1%-4% were obtained in reflection for the cesiated p-type 0.5 mum thick GaN films and 25%-50% on the 0.1 mum thick GaN films. The corresponding emission currents are 142-300 nA for 0.5 mum thick films and 0.7-1.3 muA for the 0.1 mum thick films. This results in an increase of several orders of magnitude in the emission current from the starting GaN films. Furthermore, an initial desorption measurement was performed in order to evaluate the Cs binding strength to GaN relative to GaAs. We observe Cs was bound to the GaN surface (0001) at 700 degreesC and completely desorbed at 450 degreesC for a (100) GaAs surface. Finally, an alternate barium activation on GaN is included for preliminary comparison with the various cesium activations. (C) 2000 American Vacuum Society. [S0734-211X(00)10806-6].