Activation experiment and spectral response properties analysis of graded-bandgap AlGaAs/GaAs electron-injection cathode

A cesium/oxygen activation experiment was conducted on a gallium-arsenide-based electron-injection cathode in an ultra-high vacuum system connected to a spectral response measuring instrument. Before activation, high-temperature cleaning was performed at 650 °C to obtain an atomically clean surface. The cathode surface impurities before and after the experiment were characterized by X-ray photoelectron spectroscopy. Because of the cathode Ti/Pt/Au electrode properties, the sample could not be cleaned chemically. High-temperature cathode treatment before activation could not remove the oxides completely, which led to a low cathode emission capacity in the photocurrent and spectral response. The experimental quantum efficiency curve was fitted by a two-minima diffusion model, and parameters, such as the electron diffusion length and escape probability, which characterize the cathode performance, were calculated. According to the fitting results, the residual impurities on the cathode surface and the thin emitter layer resulted in a low probability of electron escape, which resulted in a low quantum efficiency.