Work Function Measurement of Silicon Germanium Heterostructures Combining Kelvin Force Microscopy and X-ray Photoelectron Emission Microscopy

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• 作者：Sylvain Pouch ; Michele Amato ; Matteo Bertocchi ; Stefano Ossicini ; Nicolas Chevalier ; Thierry M茅lin ; Jean-Michel Hartmann ; Olivier Renault ; Vincent Delaye ; Denis Mariolle ; 艁ukasz Borowik
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：November 25, 2015
• 年：2015
• 卷：119
• 期：47
• 页码：26776-26782
• 全文大小：361K
• ISSN：1932-7455

文摘

Work function in Si_1鈥?i>xGe_x heterostructures with Ge content in the 6% to 49% range was studied with high energy resolution by combining Kelvin force microscopy and X-ray photoelectron emission microscopy. Although the two methods are based on distinct physical mechanisms, we show that both techniques give the same work function differences between each Si_1鈥?i>xGe_x layer, as small as 20 meV. To detect such small work function differences, we put in evidence the necessity of preparing the Si_1鈥?i>xGe_x sample surface with polishing, HF etching and Ar+ sputtering. Such surface preparation allows, in principle, to reduce the deleterious influence of surface states, coming for instance from carbon atoms or native oxide, on quantitative work function extraction. We show in this paper that even after such a sample surface preparation, a strong band bending can be present, which causes a contrast inversion on the surface of the material and yields an artificially lower surface work function with respect to theoretical values. By using density functional theory simulations, we demonstrate that such inversion is likely due to residual carbon present on the surface.