Efficient Carrier-to-Exciton Conversion in Field Emission Tunnel Diodes Based on MIS-Type van der Waals Heterostack.
Efficient Carrier-to-Exciton Conversion in Field Emission Tunnel Diodes Based on MIS-Type van der Waals Heterostack.
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DOI：
10.1021/acs.nanolett.7b02617
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发表时间：
2017-07
期刊：
影响因子：
10.8
通讯作者：
Shunfeng Wang;Junyong Wang;Weijie Zhao;F. Giustiniano;L. Chu;I. Verzhbitskiy;Justin Zhou Yong;G. Eda
中科院分区：
文献类型：
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作者：
Shunfeng Wang;Junyong Wang;Weijie Zhao;F. Giustiniano;L. Chu;I. Verzhbitskiy;Justin Zhou Yong;G. Eda
我们报道了基于金属-绝缘体-半导体（MIS）范德华异质堆的隧道二极管的高效载流子到激子转换和平面电致发光，该异质堆由少层石墨烯（FLG）、六方氮化硼（hBN）和单层二硫化钨（WS2）组成。这些器件具有极低的阈值电流密度，仅为几pA·μm-2，比先前报道的最佳平面EL器件的值低了几个数量级。使用参考染料，我们估计在低电流密度极限下，EL量子效率为~ 1%，这与在等效激发速率下的光致发光量子效率具有相同的数量级。我们的观察结果表明，我们的器件的效率不受载流子到激子转换效率的限制，而是受材料固有的激子到光子的产率的限制。器件特性表明，通过Fowler-Nordheim隧穿将热少数载流子（空穴）注入到n掺杂WS2中可以触发光发射，并且hBN是一种有效的空穴传输和电子阻挡层。我们的发现为范德华异质结构的智能设计和实现高效激子器件提供了新的思路。
We report on efficient carrier-to-exciton conversion and planar electroluminescence from tunnel diodes based on a metal-insulator-semiconductor (MIS) van der Waals heterostack consisting of few-layer graphene (FLG), hexagonal boron nitride (hBN), and monolayer tungsten disulfide (WS2). These devices exhibit excitonic electroluminescence with extremely low threshold current density of a few pA·μm-2, which is several orders of magnitude lower compared to the previously reported values for the best planar EL devices. Using a reference dye, we estimate the EL quantum efficiency to be ∼1% at low current density limit, which is of the same order of magnitude as photoluminescence quantum yield at the equivalent excitation rate. Our observations reveal that the efficiency of our devices is not limited by carrier-to-exciton conversion efficiency but by the inherent exciton-to-photon yield of the material. The device characteristics indicate that the light emission is triggered by injection of hot minority carriers (holes) to n-doped WS2 by Fowler-Nordheim tunneling and that hBN serves as an efficient hole-transport and electron-blocking layer. Our findings offer insight into the intelligent design of van der Waals heterostructures and avenues for realizing efficient excitonic devices.