Molecular Gating of Silicon Nanowire Field-Effect Transistors with Nonpolar Analytes

Silicon Nanowire Field Effect Transistors (Si NW FETs) have been used as powerful sensors for chemical and biological species. The detection of polar species has been attributed to variations in the electric field at the conduction channel due to molecular gating with polar molecules. However, the detection of nonpolar analytes with Si NW FETs has not yet been well understood so far. In this paper, we experimentally study the detection of nonpolar species, and model the detection process based on changes in the carrier mobility, voltage threshold, and subthreshold swing of the Si NW FET. We attribute the detection of the nonpolar species to molecular gating, due to two indirect effects: (i) the change in the dielectric medium close to the Si NW surface; and (ii) the change in the charged surface states at the functionality of the Si NW surface. The contribution of these two effects to the overall measured sensing signal is determined and discussed. The results provide a launching pad for real-world sensing applications such as environmental monitoring, homeland security, food quality control, or medicine that currently do not use Si NW FETs.