Fabrication, characterization and application of GeSn core-shell nanowires

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To fabricate vertical GeSn core-shell nanowire (NW) MOSFETs, i-Ge NWs and their core-shell heterostructures formed on heavily doped p-Si substrates using electron beam lithography (EBL) and the top-down etching (Bosch process) was investigated. The i-Ge layer deposition by chemical vapor deposition (CVD) was first investigated for optimizing thickness and crystallinity. Sets of single Ge NWs (for device fabrication) and Ge NW arrays (for characterization) with diameters ranging from 150 to 50 nm were fabricated using EBL and Bosch etching. Surface morphology, NW size, etching depth relative to pattern size, and etching conditions were investigated to obtain desirable structures. As a result of optimization, Ge NW arrays with smooth surfaces and uniform diameters in the length direction were successfully fabricated on Si substrates.The core-shell heterostructure was then formed by CVD and the shell thickness, boron doping, and crystallinity were optimized. Raman scattering was used to evaluate the hole gas accumulation in the core relative to NW size. In addition, the core-shell interface, shell crystallinity, and elemental distribution were studied by transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis. The results demonstrated a core-shell NW structure with sharp interfaces. Finally, the fabricated samples were sent to a collaborative research group for fabricating vertical core-shell NW MOSFETs. Some of the above results were presented at the conference, and we plan to compile the full results and publish them in a paper.