Tuning ultrafast electron thermalization pathways in a van der Waals heterostructure
Tuning ultrafast electron thermalization pathways in a van der Waals heterostructure
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DOI：
10.1038/nphys3620
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发表时间：
2016-05-01
期刊：
影响因子：
19.6
通讯作者：
Jarillo-Herrero, Pablo
中科院分区：
文献类型：
--
作者：
Ma, Qiong;Andersen, Trond I.;Jarillo-Herrero, Pablo
超快电子热化-通过碰撞电离（1，2）和热载流子发光（3，4）导致载流子倍增的过程-发生在材料中的光激发电子经历快速电子-电子散射（3，5 -7）以重新分配多余能量并达到电子热平衡时。由于极短的时间和长度尺度，即使使用最先进的超快激光技术，纳米器件中电子热化的测量和操纵仍然具有挑战性（8-14）。在这里，我们克服了这一挑战，利用原子薄的二维货车德瓦耳斯（vdW）材料引入一个高度可调的电子转移途径，直接与电子热化竞争。我们在石墨烯-氮化硼-石墨烯（G-BN-G）vdW异质结构（15-17）中实现了该方案，通过该异质结构，光激发载流子从一个石墨烯层传输到另一个石墨烯层。通过施加层间偏置电压或改变激发光子能量，可以控制层间载流子传输以比层内散射事件更快或更慢地发生，从而有效地调节石墨烯中的电子热化路径。我们的研究结果表明，探测和直接调制纳米材料中的电子能量传输的方法，代表了设计和实现具有定制微观特性的光电和能量收集设备的一步。
Ultrafast electron thermalization-the process leading to carrier multiplication via impact ionization(1,2), and hot-carrier luminescence(3,4)-occurs when optically excited electrons in a material undergo rapid electron-electron scattering(3,5-7) to redistribute excess energy and reach electronic thermal equilibrium. Owing to extremely short time and length scales, the measurement and manipulation of electron thermalization in nanoscale devices remains challenging even with the most advanced ultrafast laser techniques(8-14). Here, we overcome this challenge by leveraging the atomic thinness of two-dimensional van der Waals (vdW) materials to introduce a highly tunable electron transfer pathway that directly competes with electron thermalization. We realize this scheme in a graphene-boron nitride-graphene (G-BN-G) vdW heterostructure(15-17), through which optically excited carriers are transported from one graphene layer to the other. By applying an interlayer bias voltage or varying the excitation photon energy, interlayer carrier transport can be controlled to occur faster or slower than the intralayer scattering events, thus effectively tuning the electron thermalization pathways in graphene. Our findings, which demonstrate a means to probe and directly modulate electron energy transport in nanoscale materials, represent a step towards designing and implementing optoelectronic and energy-harvesting devices with tailored microscopic properties.