Simultaneous Tunable Selection and Self-Assembly of Si Nanowires from Heterogeneous Feedstock

Semiconducting nanowires (NWs) are becoming essential nanobuilding blocks for advanced devices from sensors to energy harvesters, however their full technology penetration requires large scale materials synthesis together with efficient NW assembly methods. We demonstrate a scalable one-step solution process for the direct selection, collection, and ordered assembly of silicon NWs with desired electrical properties from a poly disperse collection of NWs obtained from a supercritical fluid-liquid-solid growth process. Dielectrophoresis (DEP) combined with impedance spectroscopy provides a selection mechanism at high signal frequencies (>500 kHz) to isolate NWs with the highest conductivity and lowest defect density. The technique allows simultaneous control of five key parameters in NW assembly: selection of electrical properties, control of NW length, placement in predefined electrode areas, highly preferential orientation along the device channel, and control of NWs deposition density from few to hundreds per device. Direct correlation between DEP signal frequency and deposited NWs conductivity is confirmed by field-effect transistor and conducting AFM data. Fabricated NW transistor devices demonstrate excellent performance with up to 1.6 mA current, 10⁶-10⁷ on/off ratio and hole mobility of 50 cm² V^-1 s^-1.