利用光电子能谱研究半导体界面能级结构

Study of semiconductor interface energy level structure by photoelectron spectroscopy

摘要:

界面能级调控是目前研究优化材料性能的关键步骤之一，界面问题也是目前研究热点．以Si/MoO3界面为例，通过利用多功能光电子能谱仪在清洁后的硅片上蒸镀不同厚度的MoO3并进行XPS及UPS表征，对其表面成分及界面能级进行分析，通过UPS谱图得到功函数和价带顶，利用XPS谱图获取界面化学、界面相互作用等信息．原子力显微镜（atomic force microscope，AFM）表征结果证实，蒸镀膜的实际厚度和使用晶振表征的理论厚度相近．光电子能谱实验结果揭示：当薄膜的理论厚度低于50 ?时薄膜成分不完全是Mo6+，低于150 ?时仍能检测到Si信号；蒸镀的薄膜理论厚度达到100 ?（功函数为6.81 eV）后，功函数数值趋于稳定，这说明可以在厚度范围内通过控制蒸镀MoO3的厚度调控Si/MoO3的界面能级．在一定范围内，利用不同厚度的薄膜调控界面能级是提高材料性能的方法之一，表明光电子能谱是用于研究界面问题的有效且便捷的表征方法．

Abstract:

Interface energy level tailoring is one of the key issues in the study of optimizing material performance， and the interface issues are also a hot spot in current research. In this paper， MoO3 films of various thickness were vapor-deposited on silicon wafers， the surface composition and interface energy level of Si/MoO3 film were analyzed by XPS and UPS measurements. It was also introduced how to obtain work function and valence band maximum through UPS data， and to acquire information on interface chemistry and interface interaction from XPS spectra. The AFM measurement confirmed that the actual thickness of the vapor-deposited film is similar to the theoretical thickness measured using the crystal oscillator. The XPS results revealed that the film was not completely MoO3 when the thickness of the film is less than 50 ?， and Si signal can still be detected when the film thickness is less than 150 ?. The UPS results revealed that work function of the film tends to be stable with value of 6.81 eV as film thickness up to 100 ?. These results indicated that the interface energy level of Si/MoO3 can be adjusted by controlling the thickness of evaporated MoO3， further to improve the materials performance of materials. In summary， photoelectron spectroscopy is an effective and convenient characterization method for investigating interface issues.