Physics based Modeling of Gate Current including Fowler-Nordheim Tunneling in GaN HEMT

In this paper, we report the major conduction mechanisms of the gate leakage current (Ig) in AlGaN/GaN HEMTs and develop an analytical model for it in a surfacepotential based framework. GaN HEMTs with higher Al mole fraction in the AlGaN barrier layer experiences high electric field across this layer in the strong reverse gate bias region, leading to a significant Fowler-Nordheim (FN) tunneling current. Accurate modeling of the FN tunneling component is very important for this device along with the Poole-Frenkel (PF) emission current which dominates in relatively lower negative bias. We have demonstrated that the electric field across the barrier layer does not saturate even in very high reverse gate bias and is sufficient to increase reverse gate leakage current drastically by the FN tunneling process. Thermionic emission (TE) mechanism plays a major role in determining the forward gate current, whereas trap-assisted tunneling (TAT) current acts in the vicinity of zero gate bias. In this work, these components have been modeled and validated with the experimental data for a wide range of bias and temperature, demonstrating the weak and strong temperature dependence of FN and PF components, respectively.