Stability of Laminated Composite InGaAs Photocathodes by Cs-O-NF3 Hybrid Activation

Negative electron affinity (NEA) InGaAs photocathodes are essential for near-infrared (NIR) vacuum detection, yet they suffer from a fundamental trade-off between quantum efficiency (QE) and operational stability. Conventional Cs/O activation offers excellent stability but limited NIR response, while Cs/NF3 activation boosts NIR QE at the cost of rapid degradation. Here, we propose and systematically investigate a Cs-O-NF3 hybrid activation strategy to break this dilemma in laminated composite InGaAs photocathodes incorporating a distributed Bragg reflector. Through 24-hour continuous photocurrent decay measurements, in-situ spectral response tracking, and ex-situ XPS/UPS surface analyses, we benchmark four activation protocols (n ≥ 3 samples each). The Cs-O-NF3 hybrid activation not only achieves a 1064 nm QE of approximately 0.84% (~7x higher than Cs/O activation at ~0.12%) but also dramatically improves stability compared to Cs/NF3 activation. Specifically, the hybrid activation extends the photocurrent decay lifetime from 5.3 ± 0.5 h to 9.1 ± –0.6 h and boosts the 24-h photocurrent retention rate from 4.7 ± 0.8 to 35.2 ± 3.1%. Comprehensive surface characterization, including quantitative XPS peak fitting and atomic concentration analysis, suggests a synergistic mechanism: the co-adsorbed oxygen and fluorine species appear to form a mixed surface dipole layer that effectively suppresses both residual gas adsorption and cesium desorption. This work provides a reliable and scalable activation route to overcome the efficiency-stability trade-off, paving the way for high-performance, long-lifetime NIR InGaAs photodetectors.