Applied Physics Division , National Institute of Standards and Technology , Boulder , Colorado 80305 , United States.
Department of Physics , University of Colorado , Boulder , Colorado 80309 , United States.
Nano Lett. 2019 Feb 13;19(2):1289-1294. doi: 10.1021/acs.nanolett.8b04865. Epub 2019 Jan 29.
The development of van der Waals (vdW) homojunction devices requires materials with narrow bandgaps and simultaneously high hole and electron mobilities for bipolar transport, as well as methods to image and study spatial variations in carrier type and associated conductivity with nanometer spatial resolution. Here, we demonstrate the general capability of near-field scanning microwave microscopy (SMM) to image and study the local carrier type and associated conductivity in operando by studying ambiploar field-effect transistors (FETs) of the 1D vdW material tellurium in 2D form. To quantitatively understand electronic variations across the device, we produce nanometer-resolved maps of the local carrier equivalence backgate voltage. We show that the global device conductivity minimum determined from transport measurements does not arise from uniform carrier neutrality but rather from the continued coexistence of p-type regions at the device edge and n-type regions in the interior of our micrometer-scale devices. This work both underscores and addresses the need to image and understand spatial variations in the electronic properties of nanoscale devices.
范德华（vdW）同质结器件的发展需要具有窄带隙以及同时具有高空穴和电子迁移率的材料，以便进行双极传输，并且需要具有以纳米空间分辨率成像和研究载流子类型和相关电导率空间变化的方法。在这里，我们通过研究二维形式的 1D vdW 材料碲的 ambiploar 场效应晶体管（FET），展示了近场扫描微波显微镜（SMM）在操作过程中成像和研究局部载流子类型和相关电导率的普遍能力。为了定量理解器件中的电子变化，我们产生了局部载流子等效背栅电压的纳米分辨率图。我们表明，从传输测量确定的全局器件电导率最小值不是源于均匀的载流子中性，而是源于器件边缘的 p 型区域和我们微米级器件内部的 n 型区域的持续共存。这项工作不仅强调了而且解决了成像和理解纳米尺度器件电子特性空间变化的需求。
