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，因为大的表面积与体积比允许更有效地缓解应变。此外，它还提供了将III-V半导体材料与硅相结合的可能性，这是迈向现代半导体技术的一大步。了解和控制单个NW级别的电属性对于将它们集成到设备中是必要的。我们研究了用分子束外延和MOCVD方法在预图案化硅(111)衬底上制备的用于下一代光电子器件的GaAs/(In，Ga)As/GaAs和NiP掺杂(Ga，In)P/(Al，Ga)P径向核壳NW异质结。这种结构的性能与晶体结构的完备性密切相关，而晶体结构的完好性对载流子迁移率有很大的影响。在核-壳系统中，可能有几个用于载流子传输的通道，例如与芯相比具有较低带隙的壳，或者沿着外壳的氧化表面。此外，研究还表明，像层错这样的结构缺陷对输运性质有很大影响。我们的目标是了解这种径向核壳结构的纳米管的电学性质及其与特殊缺陷结构的关系。通过FIB/SEM和低温STM或AFM系统，以及使用安装在FIB/SEM内的钨纳米操作器探头或导电AFM/STM的尖锐金属尖端的4ppt STM，将在单个NW的衬底上进行电导率测量。然后，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联：NW内的纤锌矿(WZ)和闪锌矿(ZB)单元之间的相平衡将通过在第三代设备Petra III和第一代第四代同步辐射Max IV上使用同步辐射的X射线纳米衍射和相干衍射成像(CXDI)来确定。随着对单个NW的异地表征，甚至计划在同时进行I-V测量期间进行现场X射线衍射研究。这种现场实验将在Petra III和Max IV使用专门为X射线纳米聚焦光束线环境设计的便携式AFM/STM组合仪器来实现。这种现场研究不仅将提供单个原子力显微镜针尖的结构和电学性质的直接关联，而且还将进一步调查局部应力(由原子力显微镜尖端施加)和焦耳S加热(由于电流流动)对原子力显微镜针尖的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.