石墨烯/TMDs/BN范德华异质结构激发态双激子行为及其调制

Due to the strong Coulomb interaction, two-dimensional transition metal dichalcogenides (TMDs) exhibit rich excitonic states with large binding energy, during which, biexciton states, comprised of two electrons and two holes, are considered as promising candidates for optoelectronic and quantum applications. Although some progress has been achieved, it is noteworthy that the investigation of biexciton states is still in its infancy, and there are some interesting topics deserves to be studied. For example, how to distinguish the biexciton states with different configurations or components, or reveal the effect of dielectric screening on the biexciton states. The current proposal aims to tune the optical properties of graphene/TMDs/BN heterostructures by means of electrostatic gating and magnetic field, and distinguish the components and valley configurations of biexciton state with high thermal stability, and discuss the formation of biexciton. By changing the thickness of graphene, the effect of dielectric environment of excited-state biexciton will be studied, and the dielectric screening behavior of biexciton will be explained combined with theoretical calculations. The goals of present proposal are to further understand the intrinsic character of excited-state biexciton and the fundamental many-body interactions, and thus provide steps for the constructions of new-concept two-dimensional optoelectronic and photonic devices operating at room temperature.

由于平面内电荷间强的库伦作用，在单层过渡金属硫族化合物(TMDs)中存在丰富的激子态，其中由四粒子组成的双激子态在光电与量子器件应用中起到重要作用。目前，对单层TMDs双激子态的研究还有待进一步完善，例如，揭示不同类型双激子组成、探讨介电屏蔽对双激子的影响等。本项目以石墨烯/TMDs/BN异质结为研究对象，通过光谱技术表征异质结在静电场、磁场调制下的光学性质，准确分辨激发态双激子，揭示激发态双激子的组成、谷组态及热稳定性，探讨双激子形成机制；通过改变石墨烯层数调制异质结介电性质，借助光谱表征异质结激发态双激子行为的变化规律，同时利用第一性原理计算介电环境对激发态双激子的影响，从实验及理论上揭示介电屏蔽对异质结激发态双激子行为的影响规律。通过以上目标的实现，理解范德华异质结激发态双激子行为及其内在的多体粒子相互作用等，为拓展室温下基于多粒子态的新型二维材料光电与光子学器件奠定基础。

范德华异质结界面处的电荷转移显著影响二维材料的物理性质与器件的光电性能等。在本项目中，我们以多种不同类型的异质结构为研究对象（如石墨烯/TMDs、TMD/InSe、InSe/GaSe等），利用光谱技术（光致发光谱、时间分辨光致发光谱）、扫描探针显微技术、电学与光电测量（光电流与扫描光电流显微镜）等手段揭示了异质结构界面处的电荷转移，并利用电场、应变、介电环境等手段对该过程进行了调控。具体研究结果如下：（1）构筑了石墨烯/WS2/BN等异质结构，证实了在高温下（> 330 K）稳定存在的激发态双激子，并利用栅极电场进行了调制；构筑了石墨烯/WS2/MnPSSe异质结构，证实了激子态与磁相互作用（磁振子特性）。（2）构筑了单层MoS2/InSe第一类异质结，利用界面处单层MoS2中光生载流子向InSe转移，显著提升了InSe中光生载流子的浓度，进而使得InSe的发光强度增强了2.5倍；此外，通过栅极静电场、单轴应变及能带工程等手段改变InSe/MoS2界面处的能带排列，显著调制了InSe的光学特性及MoS2/InSe界面处的光生电荷转移效率；构筑了InSe/WSe2异质结构，利用界面处的电荷转移成功实现了WSe2极性的转变，并实现了基于WSe2的平面同质结，并用于光伏器件。（3）构筑了InSe/GaSe异质结构浮栅器件，该器件呈现出大的电滞回线，通态/关态电流比高达106，保持/耐久性能良好，在光照下，该器件表现出极具竞争力的光电检测性能和PPC/NPC特性，更重要的是，基于NPC的多位态可以接近14个状态，最小光脉冲能量约为1 pJ，有助于实现多功能、低功耗的存储器件。.在Advanced Materials、Nano Letters、Small等期刊上发表论文7篇，培养硕士生2人、本科生2人。