Effects of three-dimensional electric-field coupling on a side-gated nanotransistor

Using a two-dimensional (2D) ensemble Monte Carlo method self-consistently coupled with three-dimensional (3D) Poisson equations, a two-dimensional electron gas (2DEG)-based planar nanodevice, or a side-gated nanotransistor (SGT), is analyzed. Compared with the previous entirely 2D simulations, the extra inclusion of a 3D electric-field solver has allowed for a quantitative study of electric-field coupling beyond the active layer (2DEG). Our results show that the device characteristics are very sensitive to not only the depth of insulating trenches into the device substrate but also a change in dielectric layers on the device surface. A coating of a dielectric thin film with a thickness of only 5 nm on the device surface is enough to significantly enhance the current. Also continuously increasing the distance between a dielectric layer and the SGT surface results in an exponential decrease in the source-drain current. Moreover, the dependence of the source-drain current on the dielectric thickness is non-monotonic. The current presents a peak when the dielectric thickness is about 150 nm and then reduces to a saturated state when the dielectric thickness is more than 300 nm. We discuss these effects in terms of the special geometric structure and working principle of the SGT.