Dresden 2009 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 30: Si/Ge

HL 30.1: Talk

Wednesday, March 25, 2009, 09:30–09:45, POT 51

Comparison of the top-down and bottom-up approach to synthesise nanowire-based Si/Ge heterostructures — •Andreas Wolfsteller, Nadine Geyer, Trung-Kien Nguyen-Duc, Nikolai Zakharov, Manfred Reiche, Wilfried Erfurth, Ursel Doß, Horst Blumtritt, Peter Werner, and Ulrich Gösele — Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle (Saale), Germany

Si nanowires (NWs) and nanowire-based Si/Ge heterostructures are expected to be building blocks for future electronic and optical devices, e. g. new field-effect transistors or sensors. In principle two approaches can be applied to synthesise NWs: i) the 'top-down' approach and ii) the 'bottom-up' approach. The most common method for the latter is the vapour-liquid-solid (VLS) mechanism, which can also be applied to grow NWs by molecular beam epitaxy (MBE). However, the VLS mechanism prevents the synthesis of heterostructures with sharp interfaces and high Ge concentrations due to the general nature of the growth process via an eutectic. Furthermore, Au, which acts as the catalyst, can be incorporated into the crystal structure, possibly resulting in a significant loss of optical properties. In the 'top-down' approach the Si/Ge heterostructure is first grown by MBE as a multilayer leading to sharper interfaces and higher element concentrations with the drawback of the generation of misfit-dislocations. The NWs (40 nm diameter) are then produced by electron beam lithography and reactive ion etching. The morphology, structure and chemical composition of both kind of NWs was analyzed by TEM, SEM, and EDX.