Atomic Structure, electronic, optical and electrical properties of freestanding, passivated, and functionalized semiconductor nanowires

由于其小半径纳米线的特征在于极大的表面体积比-其表面的结构和性质因此强烈影响纳米线的机械、光学和电学行为。因此，对于纳米线的现实理论描述，包括这样的效果是至关重要的。这对于具有（i）非常小的半径（=2nm）的纳米线是直接的，其中可以直接应用平面波赝势形式主义中的常规密度泛函理论（DFT）方法，以及（ii）非常大的半径（größer als 50 nm），其中表面可以由单个刻面建模。然而，许多将在重点项目中进行的实验的规模正好在这两个边界之间，因此无法通过标准方法进行。因此，我们的目标是应用一个层次的方法，我们将开始从完善的密度泛函方法，以确定平衡几何形状，形成能，和电子结构的半导体纳米线与小半径（克莱纳铝2nm）。在握手与这些结果近似DFT方法（DFTB）将被应用到扩展这些研究的实验相关的长度尺度（高达20纳米）。该方法将应用于裸/钝化的独立和功能化的Si，Ge，SiGe，SiC和GaN纳米线。扫描隧道显微镜/光谱模拟将允许直接连接到实验。基于所确定的平衡结构，将通过将DFTB方法与非平衡格林函数技术相结合来计算输运性质。在一个完全自洽的处理与金属接触的开放边界条件，这种方法将允许研究非平衡电子输运的纳米线，并解决相干与非相干传输，电子-声子相互作用和修改电流通量的表面功能化的问题。

Due to their small radius nanowires are characterized by an extreme large surface to bulk ratio - structure and properties of their surfaces thus strongly influence the mechanical, optical, and electrical behaviour of nanowires. For a realistic theoretical description of nanonwires it is therefore crucial to include such effects. This is straightforward for nanowires with (i) very small radii (=2nm) where conventional density functional theory (DFT) methods in the plane wave pseudopotential formalism can be directly applied and (ii) very large radii (größer als 50nm) where the surface can be modelled by individual facets. However, many of the experiments which will be performed within the focused project have a size just in between these two boundaries and which are thus not accessible by the standard approaches. We therefore aim to apply a hierarchical approach where we will start from well established density-functional methods to identify the equilibrium geometry, formation energies, and electronic structure of semiconductor nanowires with small radii (kleiner als 2nm). In handshaking with these results approximate DFT methods (DFTB) will be applied to extend these studies to the experimentally relevant length scale (up to 20nm). The approach will be applied on naked/passivated freestanding and functionalised Si, Ge, SiGe, SiC and GaN nanowires. Scanning tunnelling microscopy/spectroscopy simula-tions will allow a direct connection to experiment. Based on the identified equilibrium structure transport properties will be calculated by interfacing the DFTB-method with nonequilibrium Green-function techniques. In a fully self-consistent treatment with open boundary conditions for metal contacts this approach will allow to study nonequilibrium electron transport in the nanowires and to address questions on coherent versus incoherent transport, electron-phonon interactions and the modification of current flux by surface functionalisation.