GaAs-based photocathodes are considered state-of-the-art for producing highly spin-polarized electron beams for accelerator and microscopy applications.Negative Electron Affinity (NEA) activated surfaces are required to extract highly spin-polarized electron beams from GaAs-based photocathodes, but they suffer extreme sensitivity to poor vacuum conditions that result in rapid degradation of quantum efficiency (QE). This thesis investigates unconventional activation recipes of GaAs using Te and Sb elements in addition to conventional Cs and oxygen. Photocathode parameters, such as spectral response, spin polarization, and lifetime, are characterized for various growth recipes. To conclude the thesis, GaAs photocathodes with an optimal activation recipe (Cs-Sb-O) were characterized in a high voltage environment for a high current extraction.