The photocurrent attenuation of GaAs photocathode within one hour after activation under three different vacuum pressure (5×10-9Pa, 5×10-8Pa, 5×10-7Pa) were recorded by automatically activated monitor. The results show that: the photocurrent quickly descend in the beginning and then descend linearly at a low slope; the amplitude of the quickly descending area were 10%, 14.74% and 36%separately, with the respective slope of the linear descending area were -0.00653, -0.01132and -0.02. Three samples’ gas components of H2, CH4, CO, H2O, O2, CO2 etc under the same vacuum pressure (5×10-8Pa)during photocurrent attenuation were collected by quadrupole mass spectrometer. By comparing the gas components content and the attenuation law of the photocurrent, it has been found that H2O and H2 had a greater impact on the stability of GaAs photocathode in the ultra-high vacuum environment and H2O was the predominant effect. This paper has important guiding significance and reference value in studying the stability of GaAs photocathode and the improvement of semiconductor photocathode process.
Ar+ ion etching and X-ray photoelectron spectroscopy (XPS)depth profile analysis have been performed on the native oxide layerof GaAs(100) surface. The composition of the native oxide layer,that isthe oxide phases of gallium and arsenic, was characterized precisely. It is indicated that native oxide phases on extreme surface of GaAs(100) consist of a mixture of Ga2O3, As2O3 and As2O5. Furthermore, the respective distribution of oxide phases of gallium and arsenic along the depthwere compared and analyzed.A seemingly contradictory phenomenon was found, that is As enrichment exist in total oxide layer, but the content of Ga oxide was greater than that of As oxide in the oxide layer except for the outmost surface layer.Based on the comprehensive influence of oxidation process, etching, segregation and growth process, the intrinsic mechanism of the change of oxides along etching depth was discussed. According to the analyzed results, the oxide layer of GaAs (100) surface should be divided to two layers,that is the outmost layer containing oxides of Ga and As and the intermediate layer including only oxide of Ga.The concentration of As oxides in the outmost layer and the enrichment of As in total oxide layer are derived from surface structure inhomogeneity. The throughout total oxide layer of Ga oxide is attributed to its stronger oxidability.In the present work, the system study for native oxide layer of GaAs surface provides the powerful foundation for understanding surface state of GaAs and surface treatment.
In order to improve the electronic gain and luminance gain of low-light-level image intensifiers, microchannel plates(MCP) are adopted as the electron multiplier mechanism. According to the relevant experimental analysis, the resistance between channels is a limited value. Due to there are resistive coupling between any two adjacent channel of MCP, the electron transmission and the electron multiplication in a certain channel will be interfered by its adjacent channels, This phenomenon would affect the quality of image transmission and field of view of image intensifier. In low-light condition, the input current of MCP is small, the current gain of each channel is same, MCP has the area of linear current amplification and distortion-free image transmission. But when input current is large and close to saturation, lower current in channels has more current gain, leading to the contrast change of the image. This paper analyzes the transmission properties of electrons in the channels. It is proved that there is an electrical relationship between adjacent channels,throuht the circuit equations with relevant circuit parameters such as the resistance of secondary electron emission layer, resistance of resistive layer, the resistance between two adjacent channels, and so on. The analysis method and research results provide technical guidance for the improvement of electronic gain, luminance uniformity and preparation process of MCP.