GaAs光电阴极光谱响应曲线形状的变化

利用光谱响应测试仪测试了反射式GaAs光电阴极在激活过程中以及激活后衰减过程中的光谱响应曲线，测试结果显示在这两个过程中光谱响应曲线形状都在不断发生变化。在激活过程中随着GaAs表面双偶极层的形成，阴极表面有效电子亲和势不断降低，光谱响应则不断提高，但长波响应提高得更快。在激活结束后，位于激活室中受白光照射的GaAs光电阴极由于Cs的脱附影响了双偶极层结构，阴极表面有效电子亲和势不断升高，光谱响应则不断下降，但长波响应下降得更快。上述现象无法用常用的反射式阴极量子效率公式进行解释，它们与阴极高能光电子的逸出有关。由于反射式阴极发射电子能量分布随着入射光子能量的升高而向高能端偏移，同时阴极表面势垒形状的变化对低能电子比对高能电子的影响更大，从而导致了光谱响应曲线形状的变化。

Variation of Spectral Response Curve Shape of GaAs Photocathodes

Using spectral response measuring instrument,the spectral response curves of reflection-mode GaAs photocathodes were obtained as a function of time during the process of activation and the process of illumination by white light after activation.The measured results show that the spectral response curve shape changes continuously during both processes.Due to the formation of double dipoles on the GaAs surface during the co-adsorption of cesium and oxygen,the surface electron affinity of photocathode decreases continuously,and spectral response increases continuously,but the spectral response of long wave increases faster.During the process of illumination by white light after activation,due to the double-dipole structure affected by the desorption of cesium,the surface electron affinity of photocathode increases continuously,and spectral response decreases continuously,but the spectral response of long wave decreases faster.Using traditional quantum efficiency formula of reflection-mode photocathodes,the above phenomena cannot be explained very well,and they have a relationship with the escape of high-energy electrons.Because the emitted electron energy-distribution of reflection-mode photocathodes shifts towards higher energies with the increase in photon energy,and the influence of the evolution of surface potential barrier profile on the low-energy electrons is greater,the spectral response curve shape changes during different processes.