Atomic hydrogen cleaning of semiconductor photocathodes

Negative electron affinity (NEA) semiconductor photocathodes are widely used for the production of polarized electron beams, and are also useful for the production of high brightness electron beams which can be modulated at very high frequencies. Preparation of an atomically clean semiconductor surface is an essential step in the fabrication of a NEA photocathode. This cleaning step is difficult for certain semiconductors, such as the very thin materials which produce the highest beam polarization, and those which have tightly bound oxides and carbides. Using a small RF dissociation atomic hydrogen source, we have reproducibly cleaned GaAs wafers which have been only degreased prior to installation in vacuum. We have consistently prepared very high quantum efficiency photocathodes following atomic hydrogen cleaning. Details of our apparatus and most recent results are presented