Abstract In this work, we demonstrate the application of terahertz-optical Hall effect (THz-OHE) to determine directionally dependent free charge carrier properties of ambient-doped monolayer and quasi-free-standing-bilayer epitaxial graphene on 4H–SiC(0001). Directionally independent free hole mobility parameters are found for the monolayer graphene. In contrast, anisotropic hole mobility parameters with a lower mobility in direction perpendicular to the SiC surface steps and higher along the steps in quasi-free-standing-bilayer graphene are determined for the first time. A combination of THz-OHE, nanoscale microscopy and optical spectroscopy techniques are used to investigate the origin of the anisotropy. Different defect densities and different number of graphene layers on the step edges and terraces are ruled out as possible causes. Scattering mechanisms related to doping variations at the step edges and terraces as a result of different interaction with the substrate and environment are discussed and also excluded. It is suggested that the step edges introduce intrinsic scattering in quasi-free-standing-bilayer graphene, that is manifested as a result of the higher ratio between mean free path and average terrace width parameters. The suggested scenario allows to reconcile existing differences in the literature regarding the anisotropic electrical transport in epitaxial graphene.

中文翻译：

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通过太赫兹光​​学霍尔效应解决准独立外延石墨烯中的迁移率各向异性

摘要 在这项工作中，我们展示了太赫兹光学霍尔效应 (THz-OHE) 在确定 4H-SiC(0001) 上环境掺杂单层和准独立双层外延石墨烯的方向相关自由电荷载流子特性的应用. 发现了单层石墨烯的方向独立的自由空穴迁移率参数。相比之下，首次确定了各向异性空穴迁移率参数，其在垂直于 SiC 表面台阶的方向上具有较低的迁移率，而在准自支撑双层石墨烯中沿台阶的迁移率较高。THz-OHE、纳米级显微镜和光学光谱技术的组合用于研究各向异性的起源。排除了可能的原因是台阶边缘和平台上的不同缺陷密度和不同数量的石墨烯层。由于与衬底和环境的不同相互作用，与台阶边缘和平台处的掺杂变化相关的散射机制被讨论和排除。这表明阶梯边缘在准独立式双层石墨烯中引入了本征散射，这表现为平均自由程和平均平台宽度参数之间较高的比率。建议的方案允许调和文献中关于外延石墨烯中各向异性电传输的现有差异。这表现为平均自由程和平均阶地宽度参数之间的比率较高。建议的方案允许调和文献中关于外延石墨烯中各向异性电传输的现有差异。这表现为平均自由程和平均阶地宽度参数之间的比率较高。建议的方案允许调和文献中关于外延石墨烯中各向异性电传输的现有差异。