Quantum Confinement, Surface Roughness, and the Conduction Band Structure of Ultrathin Silicon Membranes

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• 作者：Feng Chen ; Edwin B. Ramayya ; Chanan Euaruksakul ; Franz J. Himpsel ; George K. Celler ; Bingjun Ding ; Irena Knezevic ; Max G. Lagally
• 刊名：ACS Nano
• 出版年：2010
• 出版时间：April 27, 2010
• 年：2010
• 卷：4
• 期：4
• 页码：2466-2474
• 全文大小：541K
• 年卷期：0
• ISSN：1936-086X

文摘

We report direct measurements of changes in the conduction-band structure of ultrathin silicon nanomembranes with quantum confinement. Confinement lifts the 6-fold-degeneracy of the bulk-silicon conduction-band minimum (CBM), Δ, and two inequivalent sub-band ladders, Δ₂ and Δ₄, form. We show that even very small surface roughness smears the nominally steplike features in the density of states (DOS) due to these sub-bands. We obtain the energy splitting between Δ₂ and Δ₄ and their shift with respect to the bulk value directly from the 2p_3/2→Δ transition in X-ray absorption. The measured dependence of the sub-band splitting and the shift of their weighted average on degree of confinement is in excellent agreement with theory, for both Si(001) and Si(110).