Electrical and Structural characterization of single core-shell semiconductor nanowires

纳米线方法提供了在高度晶格失配的系统之间形成异质结构的可能性，因为大的表面与体积比允许更有效地释放应变。此外，它提供了将联合收割机III V半导体材料与硅结合的可能性，这是迈向现代半导体技术的一大步。了解和控制电性能在个人NW水平是必要的，他们集成到设备。研究了利用MBE和MOCVD技术在预图形化硅（111）衬底上制备的GaAs/（In，Ga）As/GaAs和NiP掺杂（Ga，In）P/（Al，Ga）P径向核壳NW异质结的光电子学性能。这种结构的性能与晶体学完整性密切相关，晶体学完整性对电荷载流子迁移率具有显著影响。在核-壳系统中，可能存在用于电荷载流子传输的若干通道，例如与核相比具有较低带隙的壳，或沿着外壳的氧化表面。此外，它建议，结构缺陷，如堆垛层错的输运性质有很大的影响。我们的目标是了解这种径向核壳纳米线的电学性质及其与特定缺陷结构的相关性。将通过FIB/SEM和低温STM或AFM系统以及通过使用安装在FIB/SEM内部的tngsten纳米操纵器探针或导电AFM/STM的尖锐金属尖端的4ppt STM，在衬底上以其生长几何形状在单个NW处进行电导率测量。选定的核壳NW的I-V特性将与相同纳米物体的详细结构特性相关：纤锌矿（WZ）和锌（ZB）单元之间的相平衡以及NW内的结构缺陷将通过X射线纳米衍射和相干衍射成像（CXDI）使用第三代设施PETRA III和第一个第四代同步加速器Max IV的同步辐射来确定。沿着对单个纳米线的非原位表征，甚至计划在同时I-V测量期间进行原位X射线衍射研究。这种原位实验将在PETRA III和Max IV使用便携式组合AFM/STM仪器实现，该仪器是专门为X射线纳米聚焦光束线环境设计的。这种原位研究不仅提供了单个NW的结构和电学特性的直接相关性，而且还研究了局部应力（由AFM针尖施加）和焦耳加热（由于电流流动）对NW结构和电导率的影响。

The nanowire approach offers the possibility to form hetero-structures between highly lattice-mismatched systems, because the large surface to volume ratio allows relieving strain more effectively. Additionally, it offers the possibility to combine III V semiconductor materials with silicon which is a large step towards modern semiconductor technology. Understanding and control of electrical properties at the individual NW level is necessary for their integration into devices. We investigate GaAs/(In,Ga)As/GaAs and nip-doped (Ga,In)P/(Al,Ga)P radial core-shell NW heterostructures fabricated by MBE and MOCVD onto pre-patternede silicon (111) substrates for next generation optoelectronic devices. The performance of such structures is strongly related to crystallographic perfection which has significant impact on charge carrier mobility. In a core-shell system there might be several channels for charge carrier transport, such as the shell with lower band gap compared to the core, or along the oxidized surface of the outer shell. Additionally, it is suggested that structural defects like stacking-faults have strong impact on transport properties. We aim to understand the electrical properties of such radial core-shell NWs and their correlation to the particular defect structure. Conductivity measurements will be perfromed at single NWs in their as-grown geometry on the substrate, by means of FIB/SEM and low-temperature STM or AFM systems and by 4ppt STM using either tngsten nano-manipulator probe installed inside the FIB/SEM or the sharp metallic tip of the conductive AFM/STM. The I-V characteristics of selected core shell NWs will then be correlated to the detailed structural properties of the same nano objects: The phase balance betweeen wurtzite (WZ) and zincblende (ZB) units and structural defects within a NW will be determined by x-ray nano-diffraction and coherent diffraction imaging (CXDI) using synchrotron radiation at 3rd generation facilities PETRA III and the first 4th generation synchrotrin Max IV. Along with the ex-situ characterisation on single NWs,even in-situ X-ray diffrcation studies during simulataneous I-V measurement is planned. This in-situ experiments will be realized both at PETRA III and Max IV using a portable combined AFM/STM instrument, which has been designed specifically for the X-ray nano-focus beamline environment. Such in-situ studies will not only provide direct correlation of structural and electrical properties of individual NWs, but furthermore investigate the influence of local stress (applied by the AFM tip) and Joule´s heating(due to current flow) on NW structure and conductivity.