Modeling the Reverse Gate-Leakage Current in GaN-Channel HFETs: Realistic Assessment of Fowler–Nordheim and Leakage at Mesa Sidewalls

A model considering different leakage paths for describing the reverse gate leakage in mesa-isolated polar GaN-channel heterostructure field-effect transistors (HFETs) is presented. For AlGaN/GaN HFETs, it is illustrated that for small negative values of gate-source bias, gate leakage happens from the gate-covered mesa sidewalls to the 2-D electron gas (2-DEG). The bias and temperature dependences of the gate current show that the sidewall path to the 2-DEG is associated with the Poole-Frenkel electron emission. As the gate-source bias becomes more negative, electrons choose a different path to the 2-DEG. In this case, results corroborate that the gate leakage is dominated by the Fowler-Nordheim (FN) direct tunneling process through the III-nitride barrier. The novel contribution of the present analysis is that it postulates that in absence of absolute uniformity, FN tunneling takes place through only a small portion of the surface of the barrier, which boasts the highest electric field or the smallest Schottky barrier height. By applying this hypothesis, the origin of the inconsistencies inherent to the previously presented models in selecting the value of the electron effective mass can be explained.