Improvement of blue green absorption of reflection mode GaAlAs photocathode with different nanostructures

Abstract

Underwater photoelectric detection equipment with 532 nm laser as light source needs to match specific photocathodes to achieve the purpose of high quantum efficiency and narrow-band response. NEA GaAlAs photocathodes have a series of advantages, such as high quantum efficiency, adjustable spectral response cutoff threshold and long lifetime to serve as the devices for underwater detection. However, the quantum efficiency of GaAlAs photocathodes is not high enough to meet the actual detection requirements. In addition, micro-nano structures on the surface of materials have been proved to be an effective method to improve optical absorption. In this paper, four kinds of nanostructures including square column, cylinder, square cone and cone are designed. By the finite difference time domain method, results show that the optical absorptivity of reflection-mode GaAlAs photocathodes can be effectively improved. The optical absorptivity of square cone nanostructures increases and tends to be stable with the increase of filling factor. The optical absorptivity is approximately 100% at blue-green light region including 532 nm, and has an abrupt cutoff feature. Otherwise, when the absorptivity of square cone nanostructures is high and stable, the most intense light absorption part will move to the top of nanostructures with the increase of filling factor, thus effectively shortening the electron transport distance and improving the photoemission capability.