GaN紫外光阴极材料的高低温两步制备实验研究

Experimental Investigation of High-Low-Temperature Two-Step Preparation of GaN UV Photocathode Material

GaN紫外光阴极是一种表面具有负电子亲和势(NEA)状态的光电发射材料,具有电子发射效率高、暗发射小、稳定性好等众多优点,是近年来得到迅速发展的一种新型高性能紫外探测材料。采用超高真空原子吸附工艺,对金属有机物化学汽相沉积(MOCVD)外延的p型GaN表面依次进行了高温净化、Cs/O激活、低温净化和Cs/O激活的高低温两步光阴极制备实验。实验结果表明,高温净化后的Cs/O激活可制备出量子效率约为20%的GaN紫外光阴极材料,第二步低温净化后GaN表面仍具有光电发射能力,经过Cs/O激活后可将阴极光电流恢复到接近高温激活结束后的水平,说明GaN阴极材料的制备只需单步高温激活完成。通过比较GaN与GaAs光阴极材料的高低温制备效果差异,对GaN光阴极制备工艺的机理进行了探讨。

GaN ultraviolet（UV）photocathode is a type of photoemission material with negative electron affinity（NEA）surface.The photocathode has high quantum efficiency,low dark current,good stability and many other virtues,therefore it has become a new-type UV detection material in recent years.Using atoms absorption technique in ultra-high vacuum system,experiments of high-low temperature two-step preparation are made on p-type MOCVD expitaxial GaN.The two-step preparation includes four steps,which are high temperature cleaning,Cs/O activation,low temperature cleaning and Cs/O activation.The experimental results show that GaN photocathode with about 20% quantum efficiency is obtained after high temperature cleaning and Cs/O activation.Photoemission current is still observed after low temperature cleaning.After subsequent Cs/O activation the photocurrent of photocathode can be restored,but the value is only close to the level after high temperature activation.This indicates that GaN photocathode material only needs single-step activation to be prepared.The differences of two-step preparation effects between GaN and GaAs photocathode material are compared,and preparation mechanisms of GaN photocathode is also discussed