Ultrathin Gate Dielectric Enabled by Nanofog Aluminum Oxide on Monolayer MoS₂

Field-effect transistors (FETs) based on two-dimensional (2D) semiconductors must have ultrathin gate dielectrics in order to achieve low voltage operation. Here we achieve conformal HfO2 gate dielectrics on monolayer MoS2 with the aid of an AlOx seed layer deposited by "nanofog,"a low temperature process at 50 °C. We study the uniformity of the nanofog layer as a function of its deposition temperature, and we also compare FETs fabricated with nanofog AlOx seed vs. electron-beam evaporated Al seed layers, followed by HfO2 dielectric. With the nanofog seed, we achieve subthreshold slope < 100 mV/dec at room temperature and equivalent oxide thickness (EOT) of 1.3 nm. Devices with nanofog exhibit nearly hysteresis-free behavior, unlike those with the Al seed, consistent with the subthreshold data showing fewer interface defects with nanofog seed layers. The "nanofog"process is thus established as a low-Temperature, industry-compatible seed layer for high-κ dielectric deposition onto 2D semiconductors.