Obtaining photocathodes with high quantum yield has been the focus during the process of photocathode development. With the limitation of basic industrial manufacturing level, the further performance improvement of the negative electron affinity photocathode is subject to the quality of grown material itself. For this reason, according to the band engineering science, we have proposed an exponential-doping structure applied to the active-layer of reflection-mode and transmission-mode AlGaAs/GaAs photocathodes via molecular beam epitaxy technique, to increase the photocathode emission efficiency. A series of theoretical and experimental researches including structure design, material growth, surface cleanness, Cs-O activation and performance evaluation have been carried out to confirm the actual effect of exponential-doping photocathodes. As a result of the built-in electric field, the cathode performance was enhanced for exponential-doping AlGaAs/GaAs photocathodes.