Four different p-type doping GaN photocathodes are activated by Cs/O, and the quantum efficiency (QE) curves are obtained. According to the QE equation, the curves are fitted. Both the QE curves and the fitting results show that the optimal p-type doping concentration is at 1017 cm−3. The electron diffusion length and surface-electron escape probability can be balanced well at 1017 cm−3. To a certain degree, thick emission layer is conducive to improving the QE, which is more obvious with the long wavelength.

Surface electronic structure in transition-metal (Cr and Mn) doped GaAs (001) studied by in situ photoemission spectroscopy Appl.In order to verify the actual effect of an exponential-doping structure on cathode performance, an exponential-doping structure has been applied to the preparation of the transmission-mode GaAs photocathode via molecular beam epitaxy technique. Compared with the uniform-doping photocathode, the activation and spectral response results show that the exponential-doping photocathode can achieve a higher photoemission capability. In addition, based on the revised uniform-doping and exponential-doping transmission-mode quantum yield equations, the cathode performance parameters such as electron average transport length and electron escape probability of the exponential-doping photocathode are obtained, which are greater than those of the uniform-doping one. The improvement in the cathode performance is attributed to the built-in electric field arising from this special doping structure, which effectively increases the electron transport efficiency and escape probability.

To confirm the actual effect of an exponential-doped structure on cathode performance, an exponential-doped structure was applied to the preparation of a transmission-mode GaAs photocathode, and spectral response curves after high-temperature activation, low-temperature activation, and the indium sealing process were separately measured by use of the on-line spectral response measurement system. The results show that, compared to the previously uniform-doped photocathode, the exponential-doped photocathode can obtain higher cathode performance and photoemission capability because of the built-in electric field. Nevertheless, cesium desorption and impurity of gas during the sealing process can cause the degeneration of spectral response in the entire response waveband, especially in the long-wavelength region, with the decrease in surface electron escape probability related to the adverse evolution of the surface potential barrier profile.

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