Surface Purification And Characterization Of Near-infrared InGaAs Photocathodes

In Ga As photocathodes are widely used in low-light image intensifiers,stripe image converters,photomultipliers and other photoelectric devices due to the advantages of adjustable near-infrared spectrum response,low dark current,concentrated electron emission energy and etc.At present,Inx Ga1-x As materials based on the Ga As substrate usually have an indium components of x=0.15~0.2.However,only few researches are reported on the surface purification processes of the In Ga As photocathodes.Also,the results vary with analysis methods,preparation processes and systems.Given this background,based on the ultra-high vacuum photocathode preparation and characterization interconnection system and scanning focused X-ray photoelectron spectroscopy technology,the surface purification processes including surface impurity adsorption,surface purification process and purification effect characterization of In Ga As photocathodes were investigated,specifically as follows:Firstly,based on first-principles calculation,the adsorbed models of carbon atoms and oxygen atoms at different positions on the As-stabilized In0.19Ga0.81As(100)?2(2×4)surface were constructed.By analyzing the geometry structure,band structure,work function,adsorption energy and optical properties of the impurity adsorption models,it is found that the adsorption of impurity atoms affected the surface atomic and electronic properties of In Ga As material of varying degrees,and the stabilities of As dimers are destroyed.After adsorption,the lengths of C?C bonds decrease,while the O-O bonds increase or even break.The surface work function after oxygen adsorption all become larger,while the work function after carbon adsorption show different changes with different positions.Secondly,a series of experiments including different chemical cleaning methods and high temperature purification with different temperatures were designed by using ultra-high vacuum photocathode preparation and characterization interconnection system and scanning focused Xray photoelectron spectroscopy(XPS)technology.The ultraviolet ozone cleaning procedure was added into the traditional chemical cleaning method.Combined with XPS surface analysis,the purification effects of different chemical etching solutions and whether the ultraviolet ozone cleaning procedure is present were compared to select the optimal cleaning method.Results show that ultraviolet ozone cleaning can greatly enhance the chemical cleaning ability to remove the surface contaminants and obtain a As-stabilized surface with least impurities.In the high temperature purification experiments,using the XPS surface analysis technology,the effects of different heating temperatures on the desorption of surface impurities and indium contents were compared.Combined with the ultraviolet photoelectron spectroscopy technology(UPS)technology,the influences of high temperature purification on surface work function were analyzed,and it was found that the surface impurities could be removed and the surface work function could be effectively reduced after heating at 600?.Finally,combining the advantages of interconnection and in-situ analysis of the experiment system,surface cesium-oxygen(Cs-O)activation experiments of In Ga As photocathodes with different chemical cleaning methods we re implemented.The effects of different surface purification processes on the photocurrent and spectral response were compared to further characterize the effectiveness of the surface purification,and it is verified that the optimized surface purification process can get better surface cleanliness and higher photoelectric emission performance.By fitting the quantum efficiency curve to compare the photocathode performance parameters,it is found that the samples with better surface cleanliness have higher electron escape probability and lower surface barrier factor.By using XPS and UPS analysis technology,the effects of surface activation on element contents,binding energy positions of element spectrum peaks and work function were compared,it was found that the element spectrum peak of In Ga As photocathodes shifted to the direction of low binding energy after activation and the surface work function declined.