Multiscale Analysis for Field-Effect Penetration through Two-Dimensional Materials

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• 作者：Tian Tian ; Peter Rice ; Elton J. G. Santos ; Chih-Jen Shih
• 刊名：Nano Letters
• 出版年：2016
• 出版时间：August 10, 2016
• 年：2016
• 卷：16
• 期：8
• 页码：5044-5052
• 全文大小：592K
• 年卷期：0
• ISSN：1530-6992

文摘

Gate-tunable two-dimensional (2D) materials-based quantum capacitors (QCs) and van der Waals heterostructures involve tuning transport or optoelectronic characteristics by the field effect. Recent studies have attributed the observed gate-tunable characteristics to the change of the Fermi level in the first 2D layer adjacent to the dielectrics, whereas the penetration of the field effect through the one-molecule-thick material is often ignored or oversimplified. Here, we present a multiscale theoretical approach that combines first-principles electronic structure calculations and the Poisson–Boltzmann equation methods to model penetration of the field effect through graphene in a metal–oxide–graphene–semiconductor (MOGS) QC, including quantifying the degree of “transparency” for graphene two-dimensional electron gas (2DEG) to an electric displacement field. We find that the space charge density in the semiconductor layer can be modulated by gating in a nonlinear manner, forming an accumulation or inversion layer at the semiconductor/graphene interface. The degree of transparency is determined by the combined effect of graphene quantum capacitance and the semiconductor capacitance, which allows us to predict the ranking for a variety of monolayer 2D materials according to their transparency to an electric displacement field as follows: graphene > silicene > germanene > WS₂ > WTe₂ > WSe₂ > MoS₂ > phosphorene > MoSe₂ > MoTe₂, when the majority carrier is electron. Our findings reveal a general picture of operation modes and design rules for the 2D-materials-based QCs.