Nonlinear optical spectroscopy at silicon interfaces
Nonlinear optical spectroscopy at silicon interfaces
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硅界面的非线性光谱
DOI：
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发表时间：
1993
期刊：
影响因子：
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通讯作者：
H. Ibach
中科院分区：
文献类型：
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作者：
W. Daum;H. Krause;U. Reichel;H. Ibach
利用可调谐激光脉冲产生的光学二次谐波（SHG）和频（SFG）研究了氧化、清洁和氢封端硅表面的界面特性。在清洁的和不同氧化的Si（100）和Si（111）表面的SHG和SFG谱中观察到一个在3.3eV光子能量处的强共振带。在氧化表面的情况下，带的外观强烈地依赖于样品的处理，但不依赖于氧化物厚度。湿化学制备的氢终止表面的光谱没有显示出明显的共振强度约3.3eV，从而证明了带的独特的界面特征。在干净的硅表面上进行的化学吸附实验排除了表面状态之间的转换所观察到的频带的原因。它的结论是，共振是由直接带隙跃迁，来自体硅中的E1跃迁在3.4eV，发生在一个薄层的硅原子与应变键清洁的Si表面的表面原子下面的Si-SiO2界面处。根据我们的结果讨论了Si-SiO_2结构中常见的界面缺陷态的U形分布。
Interface properties of oxidized, clean and hydrogen-terminated silicon surfaces have been studied by optical second-harmonic generation (SHG) and sum-frequency generation (SFG) using tunable laser pulses. A strong resonance band at 3.3eV photon energy is observed in SHG and SFG spectra of clean and various oxidized Si(100) and Si(111) surfaces. In the case of oxidized surfaces, the appearance of the band strongly depends on the treatment of the sample, but not on oxide thickness. Spectra of hydrogen-terminated surfaces prepared by wet chemistry do not reveal appreciable resonant intensity around 3.3eV thus proving the distinct interface character of the band. Chemisorption experiments performed on clean silicon surfaces rule out transitions between surface states as the reason for the observed band. It is concluded that the resonance is caused by direct band gap transitions, derived from the E1 transitions at 3.4eV in bulk silicon, that take place in a thin layer of silicon atoms with strained bonds underneath the surface atoms of clean Si surfaces and at the Si-SiO2 interface. The commonly observed U-shaped distribution of interface defect states in Si-SiO2 structures is discussed in the light of our results.