Understand and Advancing of Semiconductor Nanowire Synthesis
Hui, Ho Yee
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Semiconductor nanowires (NWs) have become an indispensable nanoscale platform for a broad range of electronic, photonic, and energy conversion applications. Among all growth technique, the bottom-up vapor-liquid-solid (VLS) nanowire (NW) fabrication technique offers the ability to encode material functionalities along the length of a NW in a user programmable manner. A robust control of VLS growth requires understanding of multiple heterogeneous chemical processes: (1) transportation of semiconductor molecules/atoms from vapor to liquid droplets or vice versa at the vapor-liquid (VL) interface, (2) crystallization and dissolution of semiconductor atoms at the liquid-solid (LS) interface, and (3) the conformal deposition of precursor molecules onto the nanowire sidewall at the vapor-solid (VS) interface. However, the ability to rationally engineer NWs for advanced semiconductor devices is critically impaired by limited understanding of these chemical processes at the heterogeneous interfaces. Here, through experiments and modeling, nanowires can be selectively removed via solid-liquid-vapor mechanism at the VL and LS interfaces. Similarly, the importance of adsorbates from a prior study at the VS interface is leveraged to fabricate large-area arrays of high quality axial Si/Ge heterostructures for the first time. These findings open the door to engineer nanowire structures along the nanowire length, a capability that can be applied to applications from high performance electronics to ultra-sensitivities (bio) molecular sensors.