Theoretical And Experimental Research On Photoemission Characteristics Of GaAs Based Wire-array Photocathodes

Due to the advantages of high quantum efficiency and low dark current, Negative-Electron-Affinity(NEA) GaAs photocathodes have shown widespread applications, such as in high performance photodetection and low-light level detection. The unique structure of wire array has applied to nano-optoelectronics and nano-solar cells. Therefore, the NEA GaAs wire-array photocathodes are becoming one of the most promising material for photoemission.In this paper, a photoemission model for GaAs wire-array photocathodes is established based on Ray-tracing method.. According to 3D simulation software Visual TCAD using the model, the photocurrent, spectral response, and absorption properties of ordered GaAs wire-array photocathodes are simulated and analyzed as a function of incident angle and wire height. Compared with GaAs film cathodes, the photoemission characteristics of wire-array cathodes are superior to that of film counterparts. We fabricated GaAs and AlGaAs wire arrays by ICP etching, and analyzed the effect of ICP etching processes on GaAs wire array. The morphology of arrays is observed by Scanning Electron Microscope(SEM); the optical property of GaAs wire arrays is characterized by micro-photoluminescence(PL) and reflectance spectrum. The results show that both PL and reflectance spectrum of wire arrays are better than films. The GaAs nanowire arrays of 500nm-diameter were prepared by Nanoimprint Lithography(NIL). Finally, GaAs wire-array photocathodes were activated by the coadsorption of cesium and oxygen in an ultra-high vacuum system. Following the activation, the spectral response curves were obtained in situ and the effect of incident angles on photoemission was analyzed. The spectral response for GaAs wire-array photocathodes verified their excellent performance.