Physics based model of an AlGaN/GaN vacuum field effect transistor

Abstract

A vacuum field effect transistor (VacFET) is proposed that consists of a modification of a conventional AlGaN/GaN high electron mobility transistor to include a nanogap near the gate on either the source (cathode) or drain (anode) side of the device. The current flowing through the two-dimensional electron gas (2DEG) under the gate is obtained using a charge-control model, which is forced to be equal to the tunneling current across the nanogap. The latter is modeled using a modified version of Simmons tunneling theory of a metal–insulator–metal junction to include the effect of barrier lowering across the nanogap. When compared to other recently fabricated VacFETs, the proposed device has potential for much higher emission current densities and transconductance levels, of the order of several hundreds of mA/mm and tens of mS/mm, respectively. For similar material parameters and physical dimensions, the proposed VacFET has a turn-on voltage that depends on the location of the nanogap on either the source or drain side of the gate. It is shown that the current–voltage characteristics of VacFETs with a nanogap either on the drain or source side of the gate are highly sensitive to their physical parameters and biasing conditions, making them a very strong candidate for chemical or gas sensing applications. This is due to the sensitivity of the tunneling current to the effective barrier height and field enhancement factor of the nanogap.