†Applied Science and Technology Graduate Program, University of California at Berkeley, Berkeley, California 94720, United States.
‡Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
Nano Lett. 2015 May 13;15(5):3249-53. doi: 10.1021/acs.nanolett.5b00454. Epub 2015 Apr 9.
Charge hopping and percolation in quantum dot (QD) solids has been widely studied, but the microscopic nature of the percolation process is not understood or determined. Here we present the first imaging of the charge percolation pathways in two-dimensional PbS QD arrays using Kelvin probe force microscopy (KPFM). We show that under dark conditions electrons percolate via in-gap states (IGS) instead of the conduction band, while holes percolate via valence band states. This novel transport behavior is explained by the electronic structure and energy level alignment of the individual QDs, which was measured by scanning tunneling spectroscopy (STS). Chemical treatments with hydrazine can remove the IGS, resulting in an intrinsic defect-free semiconductor, as revealed by STS and surface potential spectroscopy. The control over IGS can guide the design of novel electronic devices with impurity conduction, and photodiodes with controlled doping.
量子点 (QD) 固体中的电荷跳跃和渗滤已经得到了广泛的研究，但渗滤过程的微观本质仍未被理解或确定。在这里，我们使用 Kelvin 探针力显微镜 (KPFM) 首次对二维 PbS QD 阵列中的电荷渗滤途径进行成像。我们表明，在黑暗条件下，电子通过带隙态 (IGS) 而不是导带进行渗滤，而空穴通过价带态进行渗滤。这种新颖的输运行为可以通过单个 QD 的电子结构和能级排列来解释，这是通过扫描隧道谱 (STS) 测量得到的。用联氨进行化学处理可以去除 IGS，从而得到具有本征无缺陷半导体的特性，这是通过 STS 和表面电势谱证实的。对 IGS 的控制可以指导具有杂质传导的新型电子器件的设计，以及具有受控掺杂的光电二极管。
