变组分AlGaAs/GaAs透射式光电阴极分辨力特性分析

建立了变组分AlGaAs/GaAs光电阴极二维载流子输运连续性方程.在一定的边界条件下,利用数值计算方法对此方程进行求解,得到了变组分AlGaAs/GaAs光电阴极调制传递函数(MTF)理论计算模型.利用该模型计算了透射式变组分和均匀组分阴极的理论MTF,分析了分辨力与Al组分变化范围、入射光子波长、AlGaAs和GaAs层厚度的关系.计算结果表明,变组分阴极与均匀组分阴极相比,阴极分辨力显著提高.当空间频率f在100—500 lp·mm-1区间时,分辨力的提高最为明显,如当f=200 lp·mm-1时,一般可提高150%—260%.变组分阴极分辨力的提高是内建电场作用的结果,但内建电场太大时,也会由于Al组分含量过高而影响阴极的长波响应.

Resolution characteristic of graded band-gap AlGaAs/GaAs transmission-mode photocathodes

The modulation transfer function (MTF) of graded band-gap AlGaAs/GaAs transmission-mode photocathodes is numerically solved from the two-dimensional continuity equations. According to the MTF model, we calculate the theoretical MTF of graded band-gap and uniform band-gap transmission-mode photocathodes, and analyze the effects of Al composition, wavelength of incident photon, and thickness values of AlGaAs and GaAs layer on the resolution. The calculated results show that compared with the uniform band-gap photocathode, the graded band-gap structure can increase the resolution of photocathode evidently. If the spatial frequency f ranges from 100 to 500 lp·mm^-1, the increase of resolution is more pronounced. Let f=200 lp·mm^-1, the resolution of graded band-gap photocathode generally increases 150%-260%. The resolution improvement of graded band-gap photocathode is attributed to the built-in electric field. While too high built-in electric field will influence the spectral response of long-wavelength photons due to higher Al composition in the AlGaAs/GaAs photocathodes.
Keywords： graded band-gap built-in electric field resolution modulation transfer function