Modeling and performance analysis of high-speed, high-power GaN nanowire FETs

We present the first analysis of the transport properties of deeply scaled (2 nm and 4 nm diameter) GaN NW FETs. Even for the ultra-small diameter (~ 2 nm) GaN NW FET, the geometric gate capacitance CG is smaller than the quantum capacitance C_Q, and thus the NW FETs operate in the classical capacitance limit (CCL) instead of operating in the quantum capacitance limit (QCL). This is a result of the high electron effective mass (0.19 m₀ and 0.16 m₀ for the lowest conduction band, respectively, for the 2 and 4 nm diameter NWs) and consequent high density of states. For the NW FETs with source Fermi levels such that (E_F E_C) = 0.2 eV, the current density is 8.5, and 5 A/mm, respectively for the 2 and 4 nm diameter, which is 2 4 times higher than the experimental value of 2.3 A/mm for an AIN/GaN HEMT with a 3.5 nm AlN barrier . The off-current for these NW FETs is insignificant as a result of the wide bandgaps. The bandgaps for the 2 nm and 4 nm wires are 3.4 eV and 3.3 eV, respectively. The confinement has little effect on both the bandgap and conduction band effective mass. The output power is 0.06 mW and 0.07 mW for the 2 and 4 nm devices, respectively.