The factors determining quantum efficiency of field-assisted InP/InGaAsP semiconductor photocathodes have been analysed in detail in the paper. The transmission process of electrons in the absorption layer and transferred-electron process in the emission layer as well as the escape probability of electrons in the surface of emission layer have been calculated quantitatively on the basis of continuity equations and tunnelling effect of quantum mechanics. The curves of quantum efficiency versus wavelength for various biases have been obtained. The results show that the quantum efficiency of semiconductor photocathode in the range 0.9-1.25μm can be risen two orders of magnitude or more under a proper bias. It is helpful in designing the structure of semiconductor photocathodes and choose the optimum conditions of operation.
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