Abstract
A heterostructured Al(x)Ga(1-x)As/GaAs photocathode consisting of a composition-graded buffer layer and an exponential-doped emission layer is developed to improve the photoemission performance over the wavelength region of interest. The theoretical quantum efficiency models for reflection-mode and transmission-mode Al(x)Ga(1-x)As/GaAs photocathodes are deduced based on one-dimensional continuity equations, respectively. By comparison of simulated results with conventional quantum efficiency models, it is found that the multilevel built-in electric field can effectively improve the quantum efficiency, which is related to the buffer layer parameters and cathode thicknesses. This special graded bandgap structure arising from the compositional grade in the buffer layer and doping grade in the emission layer would bring about the reduction of back interface recombination losses and the efficient collection of photons generating photoelectrons. Moreover, a best fit of the experimental quantum efficiency data can be achieved with the aid of the deduced models, which would provide an effective approach to evaluate internal parameters for the special graded bandgap photoemitters.
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