Casper Clayton B, Ritchie Earl T, Teitsworth Taylor S, Kabos Pavel, Cahoon James F, Berweger Samuel, Atkin Joanna M
Department of Chemistry, University of North Carolina, Chapel Hill, NC, United States of America.
National Institute of Standards and Technology, Boulder, CO, United States of America.
Nanotechnology. 2021 May 7;32(19):195710. doi: 10.1088/1361-6528/abde63.
Electrical scanning probe microscopies (SPM) use ultrasharp metallic tips to obtain nanometer spatial resolution and are a key tool for characterizing nanoscale semiconducting materials and systems. However, these tips are not passive probes; their high work functions can induce local band bending whose effects depend sensitively on the local geometry and material properties and thus are inherently difficult to quantify. We use sequential finite element simulations to first explore the magnitude and spatial distribution of charge reorganization due to tip-induced band bending (TIBB) for planar and nanostructured geometries. We demonstrate that tip-induced depletion and accumulation of carriers can be significantly modified in confined geometries such as nanowires compared to a bulk planar response. This charge reorganization is due to finite size effects that arise as the nanostructure size approaches the Debye length, with significant implications for a range of SPM techniques. We then use the reorganized charge distribution from our model to describe experimentally measured quantities, using in operando scanning microwave impedance microscopy measurements on axial p-i-n silicon nanowire devices as a specific example. By incorporating TIBB, we reveal that our experimentally observed enhancement (absence) of contrast at the p-i (i-n) junction is explained by the tip-induced accumulation (depletion) of carriers at the interface. Our results demonstrate that the inclusion of TIBB is critical for an accurate interpretation of electrical SPM measurements, and is especially important for weakly screening or low-doped materials, as well as the complex doping patterns and confined geometries commonly encountered in nanoscale systems.
电子扫描探针显微镜（SPM）使用超尖锐金属尖端来获得纳米级空间分辨率，是表征纳米级半导体材料和系统的关键工具。然而，这些尖端并非被动探针；它们的高功函数会引起局部能带弯曲，其效应敏感地取决于局部几何形状和材料特性，因此本质上难以量化。我们使用顺序有限元模拟首先探索平面和纳米结构几何形状中由于尖端诱导能带弯曲（TIBB）引起的电荷重组的幅度和空间分布。我们证明，与体平面响应相比，在诸如纳米线等受限几何形状中，尖端诱导的载流子耗尽和积累会有显著改变。这种电荷重组是由于纳米结构尺寸接近德拜长度时出现的有限尺寸效应，这对一系列SPM技术具有重要意义。然后，我们以轴向p-i-n硅纳米线器件的原位扫描微波阻抗显微镜测量为例，使用模型中重组的电荷分布来描述实验测量的量。通过纳入TIBB，我们揭示了在p-i（i-n）结处实验观察到的对比度增强（减弱）是由尖端在界面处诱导的载流子积累（耗尽）所解释的。我们的结果表明，纳入TIBB对于准确解释电SPM测量至关重要，对于弱屏蔽或低掺杂材料以及纳米级系统中常见的复杂掺杂模式和受限几何形状尤其重要。
