High-performance CdS nanobelt field-effect transistors with high-κ HfO2 top-gate dielectrics

We have fabricated high-performance enhancement and depletion mode (E- and D-mode) top-gate metal-insulator-semiconductor field-effect transistors (T-G MISFETs) using two kinds of CdS nanobelts (NBs), labeled as NB A and NB B, respectively. High-κ HfO2 dielectric is used as the insulator layer. The thicknesses of NBs A and B are about 60 and 180 nm, respectively. The threshold voltage and subthreshold swing of the CdS NB A T-G MISFET are about 0.15 V and 62 mV/dec, respectively. The on/off ratio is about 6 × 104, which is the best result for E-mode CdS nanoFETs reported so far. The threshold voltage, on/off ratio and peak transconductance of the CdS NW B T-G MISFET are about −3.4 V, 2 × 109, and 11 µS, respectively. The on/off ratio, to the best of our knowledge, is the highest reported for nanoFETs so far. Both of the two kinds of T-G MISFETs have quite small hysteresis in their transfer characteristics. The mechanisms for the different gate transfer characteristics are discussed. Corresponding Si back-gate CdS NB MISFETs each with a 600 nm SiO2 film as the insulator layer are also measured for comparison.