Near-Infrared Absorption Enhancement of GaAs Photocathode Through “Sandwich” Micro-Nano Structure

In this paper, a nano-layered transmission GaAs photocathode structure is proposed. The near-infrared absorption of the photocathode is enhanced by inserting a “sandwich” structure of nano-SiO2 layer + Si3N4 nanopillar array + nano-SiO2 layer between the cathode optical window and the photocathode. Compared with the flat film structure GaAs photocathode used in the current third-generations image intensifiers, the optical absorption of the optimized “sandwich” structure GaAs photocathode in the near-infrared band has been significantly improved: when the wavelength λ is 868 nm and 896 nm, the optical absorption is increased by 41.69%, 55.08%, respectively. The effects of structural parameters including film thickness and grating filling medium on the light absorption of photocathode are investigated. The results show that the near-infrared light absorption enhancement is the most obvious when Si3N4 is selected as the grating filling medium for the current design, and the deposition of SiO2 film with 10 nm thickness could effectively prevent the damage of Si3N4 during bonding with the photocathode. The theoretical analyses offer important guidance in material selection and structural optimization in the grating cathode optical window used in the third-generation image intensifier for improving performance.