It was demonstrated here for the first time that photo-emission from samples under negative electron affinity could be used to study the metastable deep defects which were responsible for surface band bending and Cs/O adsorption. Optically induced pinning of the Fermi level, quenching, and the subsequent generation of photo-emission from negative electron affinity material were found be due to the presence of EL2 antisite defects and reconstructed Ga dangling bonds. By varying the external electric field, it was possible to suppress the metastable properties of the EL2 defect and thus increase the lifetime of photo-excited electrons in the band bending region. The photo-emission from negative electron affinity material could also be stimulated by using the optically activated adsorption of Cs and O, which was caused by changing the charge states of the EL2 defect and of Ga dangling bonds.

N.T.Bagraev: Materials Science Forum, 1994, 143-147, 543-8