The photo-field electron emitters (PFEEs) have been investigated by field-emission microscopy, low energy electron diffraction, Auger electron spectroscopy and Hall-effect complimentary techniques. We have found that the complete voltage-current characteristic (VCC) is nonlinear and has eight characteristic regions of current change with bias increase. The shape and the number of these regions depend highly on the state of the surface, its electrophysical parameters, and the time of the VCC measurement. An adequate model of PFEEs for the experimental results interpretation is proposed.