高温退火对GaAs光阴极表面状态的影响

Impact on surface state of high temperature annealing to GaAs photocathode

利用XPS分析了GaAs光阴极高温退火、激活前后表面组分的变化,结合光阴极退火过程中通过四级质谱仪获取的CO2、H2O、O、As、Cs等分压曲线,比较、讨论了两次退火机理的差异。提出第二次加热的目的不仅在于清洁光阴极表面,更重要的是促使第一次激活在光阴极表面形成的偶极层向更稳定的结构转化,Cs2O偶极子在高温下与GaAs本底反应生成了可在光阴极表面稳定存在的GaAs-O-Cs偶极子,形成主要由键合强的GaAs(Zn)--Cs+、GaAs-O-Cs偶极子及靠范德瓦尔斯力附着在光阴极表面的Cs2O偶极子构成的偶极层。根据这一结论,解释了光阴极两次激活过程中光电流变化规律的差异。对理解光阴极激活及表面光电发射模型具有重要意义。

The change of GaAs photocathode surface composition was analyzed by XPS before and after the photocathode was annealed and activated, combined the pressure curve of CO2, H2O, O, As, Cs obtained through four mass spectrometer while the photocathode was annealing, the difference of the two annealing was compared and discussed. It was Proposed that for the purpose of the second heating was not only cleaning photocathode surface, it was more important to procure first activated in a photocathode formed on the surface of the dipole layer is transformed to the more stable structure at high temperatures, Cs2O dipoles reacted with GaAs and generated on the photocathode surface of the stable existence of the GaAs-O-Cs dipoles, formed dipoles layer mainly by bonding strong GaAs （Zn）--Cs＋, GaAs-O-Cs dipoles and Cs2O dipoles which was attached to the photocathode surface by the Van der Waals force. Based on this conclusion, The differences of light current variation between the activation of the photocathode was explained. It was of great significance to understand the activation of the photocathode and photoelectric launch model.