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The gradient-doping structure is first applied to prepare the transmission-mode GaAs photocathode and the integral sensitivity of the sealed image tube achieves 1420 μA/lm. This paper studies the inner carrier concentration distribution of the gradient-doping transmission-mode GaAs photocathode after molecular beam epitaxy (MBE) growth using the electrochemical capacitance-voltage profiling. The results show that an ideal gradient-doping structure can be obtained by using MBE growth. The total band-bending energy in the gradient-doping GaAs active-layer with doping concentration ranging from 1 × 1019 cm−3 to 1 × 1018 cm−3 is calculated to be 46.3 meV, which helps to improve the photoexcited electrons movement toward surface for the thin epilayer. In addition, by analysis of the band offsets, it is found that the worse carrier concentration discrepancy between GaAs and GaAlAs causes a lower back interface electron potential barrier which decreases the amount of high-energy photoelectrons and affects the short-wave response.

The photocurrent and spectral response characteristics of gallium arsenide (GaAs) are obtained by a multi-information measurement system, and the evolution of the photocurrent versus the Cs:O flux ratio is investigated. The experimental results show that the photocurrent increases approximately exponentially after the first exposure to Cs until a maximum sensitivity is reached, the detailed evolution process and the ultimate photocurrent are different for different samples. These differences are analysed, and according to the process of coadsorption of Cs and oxygen on GaAs, an equation is presented to explain the increase of photocurrent.

The stability of a reflection-mode GaAs photocathode has been investigated by monitoring the photocurrent and the spectral response at room temperature. We observe the photocurrent of the cathode decaying with time in the vacuum system under the action of Cs current, and find that the Cs atoms residing in the vacuum system are helpful in prolonging the life of the cathode. We examine the evolution and analyse the influence of the barrier on the spectral response of the cathode. Our results support the double dipolar model for the explanation of the negative electron affinity effect.