Angle-dependent XPS study of the mechanisms of “high–low temperature” activation of GaAs photocathode
Angle-dependent XPS study of the mechanisms of “high–low temperature” activation of GaAs photocathode
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DOI：
10.1016/j.apsusc.2005.03.220
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发表时间：
2005-09
期刊：
影响因子：
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通讯作者：
Xiao-qing Du;Benkang Chang
中科院分区：
文献类型：
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作者：
Xiao-qing Du;Benkang Chang
利用X射线光电子能谱（XPS）对“高温”一步活化和“高低温”两步活化后的表面化学成分、原子浓度百分比和层厚进行了定量分析。结果表明，与单步激活相比，两步激活后，GaAs-O界面势垒厚度明显减小，As-O键的程度明显降低，Ga-O键占主导地位，同时（Cs，O）层厚度也有所减小，Cs/O比值基本不变。测量的光谱响应曲线表明，两步活化后，灵敏度提高了29%。为探讨GaAs（Cs，O）表面层演化对光电发射影响的内在机制，根据实验结果建立了GaAs（Cs，O）表面势垒模型。通过电子逸出几率的计算，发现GaAs-O界面势垒和（Cs，O）层厚度的减小是主要原因，从而解释了两步激活比一步激活获得更高灵敏度的原因。
The surface chemical compositions, atomic concentration percentage and layer thickness after “high-temperature” single-step activation and “high–low temperature” two-step activation were obtained using quantitative analysis of angle-dependent X-ray photoelectron spectroscopy (XPS). It was found that compared to single-step activation, the thickness of GaAs–O interface barrier had a remarkable decrease, the degree of As–O bond became much smaller and the Ga–O bond became dominating, and at the same time the thickness of (Cs, O) layer also had a deduction while the ratio of Cs to O had no change after two-step activation. The measured spectral response curves showed that a increase of 29% of sensitivity had been obtained after two-step activation. To explore the inherent mechanisms of influences of the evolution of GaAs(Cs, O) surface layers on photoemission, surface electric barrier models based on the experimental results were built. By calculation of electron escape probability it was found that the decrease of thickness of GaAs–O interface barrier and (Cs, O) layer is the main reasons, which explained why higher sensitivity is achieved after two-step activation than single-step activation.