  Several kinds of models have already been proposed for explaining the
photoemission process. The exact photoemission theory of semiconductor
photocathode was not well established after decades of research. In this paper
an integral equation of quantum efficiency (QE) is constructed to describe the
photoemission of positive electron affinity (PEA) semiconductor photocathode
based on three-step photoemission model. The influences of forbidden gap,
electron affinity, photon energy, incident angle, degree of polarization,
refractive index, extinction coefficient, initial/final electron energy,
relaxation time and external electric field on the QE of PEA semiconductor
photocathode are taken into account. In addition, a computer code is also
programmed to calculate the QE of K2CsSb photocathode theoretically at 532nm
wavelength, the result is in line with the experimental value by and large.
What are the reasons caused to the distinction between the experimental
measuring and theoretical QE are discussed.
