Electrical and Structural characterization of single core-shell semiconductor nanowires

纳米线方法提供了在高度晶格不匹配的系统之间形成异质结构的可能性，因为大的表面体积比可以更有效地缓解应变。此外，它还提供了将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。了解和控制单个NW水平的电性能对于将其集成到设备中是必要的。我们研究了用MBE和MOCVD在预图型硅（111）衬底上制备GaAs/(In,Ga)As/GaAs和掺杂（Ga,In）P/(Al,Ga)P径向核壳NW异质结构，用于下一代光电器件。这种结构的性能与晶体的完美性密切相关，而晶体的完美性对载流子的迁移率有重要影响。在核-壳系统中，载流子可能有几个通道，如带隙比核小的壳层，或沿着外层壳层的氧化表面。此外，层叠断层等结构缺陷对输运性能有较大影响。我们的目的是了解这种径向核壳NWs的电学性质及其与特定缺陷结构的相关性。通过FIB/SEM和低温STM或AFM系统，以及使用安装在FIB/SEM内的钨纳米操纵探针或导电AFM/STM的尖锐金属尖端的4ppt STM，在基板上生长几何形状的单个NWs上进行电导率测量。然后将选定的核壳NWs的I-V特性与相同纳米物体的详细结构特性相关联：纤锌矿（WZ）和锌铀矿（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）来确定，使用同步辐射在第三代设备PETRA III和第四代同步辐射设备Max IV上进行同步辐射。随着单个NW的非原位表征，甚至计划在同步I-V测量期间进行原位x射线衍射研究。该原位实验将在PETRA III和Max IV上实现，使用便携式AFM/STM组合仪器，该仪器专为x射线纳米聚焦光束线环境而设计。这种原位研究不仅可以提供单个NW结构和电学性质的直接相关性，还可以进一步研究局部应力（由AFM尖端施加）和焦耳加热（由于电流）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.