Near-infrared enhancement in thin transmission-mode GaAs photocathodes via nanostructured window layer

Facing the demand for higher quantum efficiency of transmission-mode GaAs photocathode in the near-infrared waveband, a nano-cylinder array structure is designed in the Al_0.7Ga_0.3As window layer. Through systematic optimization, the photocathode achieves a peak quantum efficiency of 39.02% at 830 nm and a maximum average quantum efficiency of 29.11% in the 700∼920 nm waveband, which are about 1.7 times and 1.4 times those of the planar photocathode, respectively. Notably, the absorptance and quantum efficiency show minimal dependence on Si₃N₄ planar layer thickness within this spectral range, offering enhanced fabrication flexibility. The near-field localization induced by the Mie resonance concentrates the light absorption near the back interface of the GaAs layer, enabling the thickness of the GaAs layer to be thinned while still maintaining a high absorptance and reducing photoelectron transport losses. This GaAs photocathode with the nano-cylinder array structure can achieve higher quantum efficiency, faster response time and lower average transverse energy in the near-infrared waveband. Meanwhile, the nanofabrication process required for this design is simple and exhibits good compatibility with the "inverted structure" manufacturing process, making it relevant for advancing the optimization of the performance of transmission-mode GaAs photocathodes. The nanostructured window layer design for GaAs photocathodes presents a promising solution for low-light imaging systems and polarized electron source applications that require both a thin emission layer and high near-infrared quantum efficiency characteristics.