Experiment and analysis of (Cs,O) activation for NEA photocathode preparation

Abstract

On-line spectral response measurement technology and angular-dependent X-ray photoelectron spectroscopy (XPS) technology are firstly used to research the (Cs,O) activation of Gallium arsenide (GaAs) negative electron affinity (NEA) photocathode. Dynamic spectral response can be obtained from on-line spectral response measurement system and by use of the computer program for quantitative angular-dependent XPS, atom concentration and layer thickness of activation layer can be calculated. The photocathode properties for evaluating (Cs,O) activation, such as the surface electron escape probability, diffusion length and so on are also calculated by simulation method. From our experimental results, optimum cesium deposition quantity is obtained when photocurrent arrives at peak value and then decreases to 10% of the maximum, and optimum oxygen deposition quantity is obtained when photocurrent arrives at peak value and then decreases to 90% of the maximum. And the photoemission peaks at 0.71 monolayer of Cs coverage. In our experimental system the optimum thickness of activation layer is 0.82 nm and interfacial oxidation layer is 0.2 nm for successfully activated GaAs NEA photocathode. Mechanism of interfacial barrier formation and effect of oxygen on the surface of activation layer are explained.