Tunable Exciton Funnel Using Moir茅 Superlattice in Twisted van der Waals Bilayer
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- 作者：Menghao Wu ; Xiaofeng Qian ; Ju Li
- 刊名：Nano Letters
- 出版年：2014
- 出版时间：September 10, 2014
- 年：2014
- 卷：14
- 期：9
- 页码：5350-5357
- 全文大小：687K
- ISSN：1530-6992
文摘
A spatially varying bandgap drives exciton motion and can be used to funnel energy within a solid ( Nat. Photonicspan class="NLM_x"> pan>2012pan class="NLM_x">, pan>6pan class="NLM_x">, pan>866鈭?72). This bandgap modulation can be created by composition variation (traditional heterojunction), elastic strain, or in the work shown next, by a small twist between two identical semiconducting atomic sheets, creating an internal stacking translation u(r) that varies gently with position r and controls the local bandgap Eg(u(r)). Recently synthesized carbon/boron nitride ( Nat. Nanotechnol.pan class="NLM_x"> pan>2013pan class="NLM_x">, pan>8pan class="NLM_x">, pan>119) and phosphorene ( Nat. Nanotechnol.pan class="NLM_x"> pan>2014pan class="NLM_x">, pan>9pan class="NLM_x">, pan>372) may be used to construct this twisted semiconductor bilayer that may be regarded as an in-plane crystal but an out-of-plane molecule, which could be useful in solar energy harvesting and electroluminescence. Here, by first-principles methods, we compute the bandgap map and delineate its material and geometric sensitivities. Eg(u(r)) is predicted to have multiple local minima (鈥渇unnel centers鈥? due to secondary or even tertiary periodic structures in-plane, leading to a hitherto unreported pattern of multiple 鈥渆xciton flow basins鈥? A compressive strain or electric field will further enhance Eg-contrast in different regions of the pseudoheterostructure so as to absorb or emit even broader spectrum of light.