Nanocylinder array AlGaAs photocathodes with enhanced spectral response and extended lifetime for the blue–green waveband

As a photoemission material capable of achieving the negative electron affinity (NEA) surface through activation, AlGaAs has found applications in fields such as low-light detection and polarized electron sources. It possesses a tunable bandgap and spectral response range, which matches the requirements of deep-sea 532 nm laser communication and underwater target recognition utilizing the blue–green window. However, the spectral response of AlGaAs photocathodes remains relatively low, making it difficult to meet the performance demands in practical applications. Through simulation optimization using the finite difference time domain (FDTD) method, a nanocylinder array (NCA) was designed on the emission surface of the AlGaAs photocathode. Under the effect of Mie resonance, the absorptance was effectively improved, and the transport distance was reduced. The chemical etching, high-temperature annealing, and activation experiments were sequentially performed on both nanostructured and planar AlGaAs photocathodes to explore their differences from planar counterparts. After Cs-O and Cs-F activation, the spectral response of the NCA photocathode reached 1.33 times and 1.6 times that of the planar photocathode, and its lifetime reached 10 times and 6 times that of the planar photocathode, respectively. This verifies the effectiveness of significantly enhancing the photoemission performance of AlGaAs photocathodes through NCA.