Lu Yang, Chen Tongxin, Mkhize Nhlakanipho, Chang Ren-Jie, Sheng Yuewen, Holdway Philip, Bhaskaran Harish, Warner Jamie H
Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom.
Walker Department of Mechanical Engineering, The University of Texas at Austin, 204 East Dean Keeton Street, Austin, Texas 78712, United States.
ACS Nano. 2021 Dec 28;15(12):19570-19580. doi: 10.1021/acsnano.1c06587. Epub 2021 Dec 3.
Two-dimensional (2D) photodetectors based on photovoltaic effect or photogating effect can hardly achieve both high photoresponsivity and large linear dynamic range at the same time, which greatly limits many practical applications such as imaging sensors. Here, the conductive-sensitizer strategy, a general design for improving photoresponsivity and linear dynamic range in 2D photodetectors is provided and experimentally demonstrated on vertically stacked bilayer WS/GaS under a parallel circuit mode. Owing to successful band alignment engineering, the isotype type-II heterojunction enables efficient charge carrier transfer from WS, the high-mobility sensitizer, to GaS, the low-mobility channel, under illumination from a broad visible spectrum. The transferred electron charges introduce a reverse electric field which efficiently lowers the band offset between the two materials, facilitating a transition from low-mobility photocarrier transport to high-mobility photocarrier transport with increasing illumination power. We achieved a large linear dynamic range of 73 dB as well as a high and constant photoresponsivity of 13 A/W under green light. X-ray photoelectron spectroscopy, cathodoluminescence, and Kelvin probe force microscopy further identify the key role of defects in monolayer GaS in engineering the band alignment with monolayer WS. This work proposes a design route based on band and interface modulation for improving performance of 2D photodetectors and provides deep insights into the important role of strong interlayer coupling in offering heterostructures with desired properties and functions.
基于光伏效应或光闸效应的二维（2D）光电探测器很难同时实现高光响应度和大线性动态范围，这极大地限制了成像传感器等许多实际应用。在此，我们提出了一种导电敏化剂策略，这是一种用于提高二维光电探测器光响应度和线性动态范围的通用设计，并在垂直堆叠的双层WS/GaS上以并联电路模式进行了实验验证。由于成功的能带对准工程，在宽可见光谱的光照下，同型II型异质结能够实现电荷载流子从高迁移率敏化剂WS高效转移到低迁移率通道GaS。转移的电子电荷引入了一个反向电场，有效地降低了两种材料之间的能带偏移，随着光照功率的增加，促进了从低迁移率光载流子传输到高迁移率光载流子传输的转变。我们在绿光下实现了73 dB的大线性动态范围以及13 A/W的高且恒定的光响应度。X射线光电子能谱、阴极发光和开尔文探针力显微镜进一步确定了单层GaS中的缺陷在与单层WS进行能带对准工程中的关键作用。这项工作提出了一种基于能带和界面调制的设计路线，以提高二维光电探测器的性能，并深入洞察了强层间耦合在提供具有所需特性和功能的异质结构中的重要作用。
