Millimeter-long silicon nanowires with uniform electronic properties: controlled synthesis, functionalization, and applications

Abstract

One-dimensional semiconductor nanowires have attracted increasing interest due to their potential device applications as well as novel physical properties. In particular, ultralong one-dimensional (1D) nanostructures can serve as the unique building blocks that interlink the nanometer-scale world with real macroscopic world. Here we report the chemical vapor deposition (CVD) synthesis of millimeter-long silicon nanowires (SiNWs) by introducing disilane (Si2H6) as reactive gas source. For 1 hr growth, the longest SiNWs can reach ~3.5 mm and their aspect ratios extend up to ~100,000 while the diameters are uniform along the wires. The average growth rate at 400 ºC is 31 ?m/min, which is roughly 130 times higher than that for silane (SiH4) at the similar growth conditions. Significantly, millimeter-long SiNWs preferred to grow along the <110> direction without exhibiting diameter-dependent preference, which is contradictory to the previous experimental observations and the predictions based on thermodynamic models. The anomalous growth habits might be driven by growth kinetics, representing a new criterion that affects the crystallographic orientation during the precipitation in VLS synthesis. More importantly, these ultralong nanowire building blocks have been configured as multiple field-effect transistor (FET) arrays by wiring hundreds of electrodes onto the single wires. The transport measurements demonstrated uniform electrical properties along the entire length of wires, and each device can behave as a reliable FET with an on-state current of ca. 1-2 ?A, a threshold voltage of 5-7 V, and peak transconductance of 160-270 nS with a maximum value of 360 nS. We converted the multiple FETs into biological sensor arrays by functionalizing SiNW surfaces with monoclonal antibodies (mAbs), and studied the multiplexed electrical detection of cancer markers. Finally, SiNWs were further coupled with functional oxides to demonstrate non-volatile memory devices.