One-dimensional carrier systems in nanowire-based semiconductor heterostructures

本项目的两个主要目标是在一维纳米线平台上实现先进的一维量子限制半导体异质结构及其结构、光学和电学输运性质的相关性。对于分子束外延生长，我们追求两条独立的路线来实现真正的量子限制一维载流子系统。虽然量子限制的二维量子威尔斯和零维量子点的可控合成最近已经建立，一维量子线仍然是最后缺失的元素，尽管纳米线模板固有的一维几何性质。此外，应变工程的范例，基于平面异质结构的无数器件的关键必须转移到纳米线。然而，它们的一维几何形状允许有效的应变松弛。因此，需要全新的应变工程策略来充分利用这一尚未探索的关键调谐parameter.We的方法来实现这样的量子线是基于GaAs基材料系统使用（i）直径控制的超薄纳米线芯和（ii）径向多壳纳米线异质结构。这种合成的异质结构纳米线的特征在于一方面相对于它们的结构（晶体结构，缺陷，化学组成，应变）和它们的量子化能谱。另一方面，我们通过光学探测由具有高空间和时间分辨率的表面声波诱导的时空载流子动力学和数值模拟来访问纳米线中不同受限载流子系统的本征输运特性。这次接触的结果之间的直接关联更少的电学和光学特性以及结构研究将揭示局部微结构之间的潜在互连（界面粗糙度，不同晶相的混合，合金成分，应变）和单个纳米线内的电学性质。从这些互补和相关的研究中，我们将获得用于器件应用的定制异质结构纳米线的优化策略。特别是，我们的目标是定制的价带结构在这些系统中的静态外延应变。使用声光光谱，我们的目标是证明应变诱导的光空穴基态与改善的电输运性质所产生的空穴迁移率的显着增加。

The two major goals of this project are the realization of advanced one-dimensional quantum confined semiconductor heterostructures on an inherently one-dimensional nanowire platform and the correlation of their structural, optical and electrical transport properties.For the growth using molecular beam epitaxy, we pursue two independent routes to implement true quantum confined one-dimensional carrier systems. While the controlled synthesis of quantum-confined two-dimensional quantum wells and zero-dimensional quantum dots has been established recently, one-dimensional quantum wires have remained the final missing element, despite the inherently one-dimensional geometric nature of the nanowire template.Moreover, the paradigm of strain engineering, key for a myriad of devices based on planar heterostructures has to be transferred to nanowires. However, their one-dimensional geometry allows for efficient strain relaxation. Thus, radically new strategies for strain engineering are required to fully exploit the potential of this yet almost unexplored key tuning parameter.Our approach to realize such quantum wires is based on the GaAs-based material systems using (i) diameter-controlled ultra-thin nanowire cores and (ii) radial multi-shell nanowire heterostructures. Such synthesized heterostructure nanowires are characterized on one side with respect to their structural (crystal structure, defects, chemical composition, strain) and their quantized energy spectrum. On the other side, we access the native transport characteristics of different confined carrier systems in the nanowire by optically probing the spatio-temporal carrier dynamics induced by a surface acoustic wave with high spatial and temporal resolution and numerical simulations.Finally, the direct correlation of the results of this contact-less electrical and optical characterization and that of structural investigations will reveal the underlying interconnections between the local microstructural (interface roughness, mixing of different crystal phases, alloy composition, strain) and electrical properties within single nanowires.From these complementary and correlation studies we will derive strategies for the optimization of tailored heterostructure nanowires for device application. In particular, we aim to tailor the valence band structure in these systems by static epitaxial strain. Using acousto-optical spectroscopy we aim to demonstrate a strain-induced light hole ground state with improved electric transport properties arising in a dramatic increase of the hole mobility.