Comparison of blue-green response between transmission-mode GaAsP- and GaAs-based photocathodes grown by molecular beam epitaxy

In order to develop the photodetector for effective blue-green response, the 18-mm-diameter vacuum image tube combined with the transmission-mode Al0.7Ga0.3As0.9P0.1/GaAs0.9P0.1 photocathode grown by molecular beam epitaxy is tentatively fabricated. A comparison of photoelectric property, spectral characteristic and performance parameter between the transmission-mode GaAsP-based and blue-extended GaAs-based photocathodes shows that the GaAsP-based photocathode possesses better absorption and higher quantum efficiency in the blue-green waveband, combined with a larger surface electron escape probability. Especially, the quantum efficiency at 532 nm for the GaAsP-based photocathode achieves as high as 59%, nearly twice that for the blue-extended GaAs-based one, which would be more conducive to the underwater range-gated imaging based on laser illumination. Moreover, the simulation results show that the favorable blue-green response can be achieved by optimizing the emission-layer thickness in a range of 0.4 mu m-0.6 mu m.