Enhancement-mode CdS nanobelts field effect transistors and phototransistors with HfO2 passivation

Abstract

As typical direct bandgap II–VI semiconductors, quasi-one dimensional CdS nanowires, nanobelts, and nanorods have shown great potential in electronic and optoelectronic applications. However, most nano-scale CdS Field Effect Transistors (FETs) work in the depletion-mode (D-mode) due to the high unintentional n-type doping concentration, which results in high power consumption under off-state. In addition, the large dark current limits to the specific detectivity when they are fabricated into phototransistors. Here, we have synthesized single crystal CdS nanobelts (NBs) on a SiO2/Si substrate via chemical vapor deposition. The CdS NB FETs were fabricated with HfO2 as a passivation layer. It is found that the working mode of the FETs was transformed from the D-mode to the enhancement-mode with the threshold voltage changing from −22.6 to 0.7 V due to the decrease in the defect density. The HfO2 passivated CdS NB phototransistor shows a responsivity of 4.7 × 104 A/W and an ultrahigh detectivity of 9.07 × 1014 Jones at the source-drain voltage of 1 V under an illumination wavelength of 450 nm. Our work demonstrates an effective way to achieve enhancement-mode CdS FETs and high performance phototransistors.