We have fabricated Si nanowire (SiNW) based ion-sensitive field effect transistors (ISFETs) for biosensing applications. The ability to prepare a large number of sensors on a wafer, the use of standard silicon microfabrication techniques resulting in cost savings, and potential high sensitivity are significant advantages in favor of nanoscale SiNW ISFETs. The SiNW ISFETs with embedded Ag/AgCl reference electrode were fabricated on a standard silicon-on-insulator wafer using electron-beam lithography and conventional semiconductor processing technology. The current–voltage characteristics show an n-type FET behavior with a relatively high on/off current ratio, reasonable sub-threshold swing value, and low gate-leakage current. The pH responses of the ISFETs with different pH solutions were characterized at room temperature which showed a clear lateral shift of the drain current vs. gate voltage curve with a change in the pH value of the solution and a sensitivity of 40 mV pH⁻¹. The low frequency noise characteristics were investigated to evaluate the signal to noise ratio and sensing limit of the devices.

The electronic and photoconductive characteristics of CdTe nanowire-based field effect transistors were studied systematically. The electrical characterization of a single CdTe nanowire FET verifies p-type behavior. The CdTe NW FETs respond to visible-near infrared (400–800 nm) incident light with a fast, reversible and stable response characterized by a high responsivity (81 A W⁻¹), photoconductive gain (∼2.5 × 10⁴%) and reasonable response and decay times (0.7 s and 1 s, respectively). These results substantiate the potential of CdTe nanowire-based photodetectors in optoelectronic applications.

Au nanoparticle (AuNP)-decorated silicon nanowire (SiNW) field-effect transistors (FETs) were made using a top-down technique to enhance the sensing responses and long-term reliability for the detection of ammonia (NH3). The as-fabricated, diluted hydrofluoric acid (dHF)-treated, and AuNP-decorated SiNW FETs were prepared and characterized at room temperature. These SiNW FETs show better sensitivity and low power consumption in the subthreshold regime than in the linear regime. To evaluate the long-term responses, devices were operated over a period of 120 days. The dHF-treated SiNW FET showed a significant degradation in sensitivity as a function of time, even though it showed the highest sensitivities in the initial stage. The SiNW with AuNPs showed the lowest long-term variation of sensitivity with sufficient linearity. The SiNW with AuNPs showed the lowest drift as low as -0.067%/day for current sensitivity and -0.024%/day for voltage sensitivity, respectively. These results suggest that the deposition of AuNPs on SiNW is very useful for improving the long-term variation in chemical sensing applications.

The low-frequency noise in the silicon nanowire field-effect transistor (SNWFET) is characterized using SNWFETs with different channel diameters d_NW. The current density and the simulation result indicate that the volume inversion as manifested by the spatial charge distribution is enhanced in smaller d_NW. The measured noise data are discussed based on the number and correlated mobility fluctuation model. It is shown that the low-frequency noise decreases in smaller d_NW. This d_NW-dependent noise behavior is clarified in terms of the effective oxide trap density and the fraction of inversion charges near the Si-SiO₂ interface.