MBE梯度掺杂GaAs光电阴极激活实验研究

Activation of Gradient Doping GaAs Photocathodes Grown by Molecular Beam Epitaxy

本文首次利用分子束外延(MBE)生长了多种由体内到表面掺杂浓度由高到低的梯度掺杂反射式GaAs光电阴极材料,并进行了激活实验,结果表明,表面低掺杂浓度适中,外延层厚度2μm^3μm以及衬底为重掺杂p型GaAs的梯度掺杂GaAs光电阴极能够获得较高灵敏度。在优化激活工艺的条件下,梯度掺杂GaAs光电阴极获得了1798μA/lm的最高积分灵敏度,比采用同样方法制备的均匀掺杂GaAs光电阴极高30%以上。梯度掺杂GaAs光电阴极表面掺杂浓度较均匀掺杂的低,第一次给Cs时间较长,第一次Cs、O交替时要调整好Cs/O比,并在整个激活过程中保持不变。一个高量子效率梯度掺杂GaAs光电阴极的获得依赖于梯度掺杂结构和激活工艺两个方面的优化。

A novel gradient doping technique has been successfully developed, in which dopant concentration on the surface is lower than that of the epitaxial layers grown by molecular beam epitaxy（MBE）.A variety of MBE reflecfion-mode GaAs photocathode materials were grown and doped by gradient doping,and activated for the first time. We found that fairly high integral sensitivity, can be achieved for the gradient doped GaAs photo-cathodes fihns,2 - 3μm thick with low surface dopant concentration, eptixially grown on heavily doped p-type GaAs（100） substrate. With optimized activation, the highest integral sensitivity, 1798μA/lm, is 30% higher than that of the conventional uniformly-doped photocathode materials. Since the surface dopant concentration of the gradient doped GAs photocathodc is lower than that of the uniformly doped GAs photocathode, the activation technique should be modified.The first Ca addition time should be longer and the current ratio of Cs and O in the initial（Cs, O） alternation should be carefully modulated and kept unchanged in the course of activation. We concluded that dopant profile and activation technique signficantly affect the quantum efficiency of gradient doped GaAs photocathode materials. There is still much room for improvement of these two factors.