用变角XPS定量分析研究GaAs光电阴极激活工艺

用变角X射线光电子能谱 (XPS)技术分析了GaAs光电阴极的激活工艺 ,定量计算了阴极表面激活层和界面氧化层的厚度和组成。界面氧化物是由于O原子穿过激活层 ,扩散到GaAs与 (Cs,O)激活层的界面上而形成的。导入过量O会增加O GaAs界面层的厚度 ,而对 (Cs,O)激活层厚度影响较小。在激活过程中 ,严格控制和减少每次导入的O量是减少界面氧化层厚度 ,提高灵敏度的重要途径。在第一步激活后的阴极样品 ,通过较低温度的加热和再激活 ,能获得比第一步高出 30 %的光电灵敏度的原因是较低温度加热减少了界面氧化层的厚度和界面势垒

Quantitative Angle Dependent XPS Studies of Activation of GaAs Photocathode

Cs,O)activated p GaAs(100)surfaces have been studied with quantitative angle dependent X ray photoelectron spectroscopy(XPS).The thickness and compositions of both the(Cs,O)activation layers and the oxidation layers of the GaAs photocathode were quantitatively evaluated.The results show that oxygen in the activation layer may diffuse to and oxidize the interfacial layers.Excess oxygen admission during activation strongly increases the thickness of the interfacial oxidation layer whilst the thickness of the(Cs,O)activation layer remains constant.We suggest that the oxidation interfacial layer can be minimized by careful control and reduction of oxygen admission at every(Cs,O)activation step so as to improve the sensitivity of the photocathode. 30% higher sensitivity can be obtained by low temperature annealing and reactivating the initially activated samples because low temperature annealing decreases the oxidation layer thickness and considerably reduces the interfacial barrier height and width.