用于激子器件应用的栅极可调谐trion开关
Gate-tunable trion switch for excitonic device applications
摘要：
三电子是具有正电荷或负电荷的激子物质，因此，与中性激子不同，三电子的流动可以产生净可检测的电荷电流。在有利的掺杂条件下，可以使用共振激发以相干方式产生三电子。在这项工作中，我们利用这些属性，以证明在几层石墨烯/单层WS 2/单层石墨烯垂直异质结的栅极控制trion开关。通过使用高分辨率的光谱扫描，通过温度控制的WS 2夹层的带隙的变化，我们得到了一个依赖于栅极电压的垂直光电流强烈依赖于激发的光谱位置，和光电流最大化时，激发能与trion峰位置共振。此外，由此产生的谐振光电流可以通过通过底部单层石墨烯的不完全屏蔽而施加的背栅电压来有效地控制，并且光电流与栅极依赖的三电子强度强烈相关，而非谐振光电流仅表现出弱的栅极依赖性-明确地证明了在谐振下的三电子驱动的光电流产生。我们估计该器件的开关时间低于100 fs。这一发现对层状材料中超快激子器件的演示是有用的。
英文摘要：
Trions are excitonic species with a positive or negative charge, and thus, unlike neutral excitons, the flow of trions can generate a net detectable charge current. Trions under favourable doping conditions can be created in a coherent manner using resonant excitation. In this work, we exploit these properties to demonstrate a gate controlled trion switch in a few-layer graphene/monolayer WS2/monolayer graphene vertical heterojunction. By using a high resolution spectral scan through a temperature controlled variation of the bandgap of the WS2 sandwich layer, we obtain a gate voltage dependent vertical photocurrent strongly relying on the spectral position of the excitation, and the photocurrent maximizes when the excitation energy is resonant with the trion peak position. Further, the resonant photocurrent thus generated can be effectively controlled by a back gate voltage applied through the incomplete screening of the bottom monolayer graphene, and the photocurrent strongly correlates with the gate dependent trion intensity, while the non-resonant photocurrent exhibits only a weak gate dependence -unambiguously proving a trion driven photocurrent generation under resonance. We estimate a sub-100 fs switching time of the device. The findings are useful towards demonstration of ultra-fast excitonic devices in layered materials.
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