二维材料热电子晶体管的基区热载流子弛豫过程实验研究

本项目提出一种新的测量二维材料热电子方法，通过以石墨烯或MoS2为代表的热电子晶体管输出特性，得到基区热电子能谱，从而获得电子间散射，电子和光学声子、声学声子的散射以及二维材料中较特殊的电子—缺陷—声子三体散射过程的信息。这有别于以光学pump-probe技术为主的常用测量手段。热电子晶体管采用垂直范德华异质结或平面分立栅定义同质结制备。目前，二维材料的研究主要集中在费米面附近平衡态冷电子的输运特性，对于远离平衡态的热电子行为的关注较少。以石墨烯为代表的二维材料中，由于相对较高的光学声子能量和较小的相空间，热电子弛豫时间相对更长，因此可看到诸如热电子倍增、光热电效应等现象。对于模拟器件，二维材料由于原子级厚度，有望获得极短的基区渡越时间，提高速度；对于数字器件，热电子晶体管可获得不依赖于二维材料禁带的大开关比。二维材料热电子晶体管以其材料和结构的特殊性，将提供传统三维半导体不可替代的优势。

We propose a new method different from the commonly-used optical pump-probe method to analyze the hot electron transport in 2D materials. By utilizing the hot electron transistor (HET) structure with 2D material base (e.g. graphene, MoS2, etc.), we can measure the output characteristics and get the so-called hot electron spectroscopy, which contains the details of hot electron energy relaxation process in the base region. Specifically, the information of electron-electron interaction, electron-optical phonon, electron-acoustic phonon, and even more complicated electron-disorder-acoustic phonon (supercollision) process can be captured as peaks and broadening in the spectroscopy. HET is fabricated by vertical vdW heterostructure or planar 2D transistor with split-gate-defined barrier region. Transport properties around Fermi level (i.e. near equilibrium) of 2D materials are well studied. However, in these systems, the electron dynamics far from equilibrium are relatively less studied. In the meantime, hot electron behaviors like hot electron multiplication and photothermoelectric (PTE) effect in graphene, caused by the relatively higher optical phonon energy and smaller phase space for effective cooling, can be analyzed by the proposed hot electron spectroscopy method. Finally, the HET is both an analog device with potential high speed due to very short base transit time and a digital device with high on/off ratio irrelative to the bandgap of 2D materials.