Comparative study of GeO2/Ge and SiO2/Si structures on anomalous charging of oxide films upon water adsorption revealed by ambient-pressure X-ray photoelectron spectroscopy
Comparative study of GeO2/Ge and SiO2/Si structures on anomalous charging of oxide films upon water adsorption revealed by ambient-pressure X-ray photoelectron spectroscopy
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DOI：
10.1063/1.4962202
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发表时间：
2016-09
影响因子：
3.2
通讯作者：
D. Mori;H. Oka;T. Hosoi;K. Kawai;M. Morita;E. Crumlin;Zhi Liu;Heiji Watanabe;Kenta Arima
中科院分区：
文献类型：
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作者：
D. Mori;H. Oka;T. Hosoi;K. Kawai;M. Morita;E. Crumlin;Zhi Liu;Heiji Watanabe;Kenta Arima
研究了GeO_2/Ge和SiO_2/Si两种结构的X射线光电子能谱（XPS）中氧化物峰和体峰之间的能量差。这是通过在高达15%的相对湿度（RH）的各种值下获得XPS光谱来实现的。相对湿度高于10 - 4%RH时，Ge上的热GeO 2比Si上的热SiO2的能量位移增加更显著，这是由于大量的水分子渗透到GeO 2膜中形成羟基。分析这种能量移动的起源，我们提出，部分羟基化的GeO 2膜，这是无关的X射线照射的正电荷，导致更大的能量移动的GeO 2/Ge比SiO2/Si。这种内在的正电荷的一个可能的微观机制是从吸附的水物种的GeO 2膜的suboxide层中的Ge散装的电子的发射，留下不动的阳离子或带正电的状态的氧化物。这可能与所报道的具有空气暴露的GeO 2层的金属氧化物半导体二极管中的平带电压的负偏移有关。
The energy difference between the oxide and bulk peaks in X-ray photoelectron spectroscopy (XPS) spectra was investigated for both GeO2/Ge and SiO2/Si structures with thickness-controlled water films. This was achieved by obtaining XPS spectra at various values of relative humidity (RH) of up to ∼15%. The increase in the energy shift is more significant for thermal GeO2 on Ge than for thermal SiO2 on Si above ∼10−4% RH, which is due to the larger amount of water molecules that infiltrate into the GeO2 film to form hydroxyls. Analyzing the origins of this energy shift, we propose that the positive charging of a partially hydroxylated GeO2 film, which is unrelated to X-ray irradiation, causes the larger energy shift for GeO2/Ge than for SiO2/Si. A possible microscopic mechanism of this intrinsic positive charging is the emission of electrons from adsorbed water species in the suboxide layer of the GeO2 film to the Ge bulk, leaving immobile cations or positively charged states in the oxide. This may be related to the reported negative shift of flat band voltages in metal-oxide-semiconductor diodes with an air-exposed GeO2 layer.