Forward gate current modeling of AlGaN/AlN/GaN HEMTs based on Poisson–Schrödinger and direct tunneling equations

In this study, we present a forward gate current model for AlGaN/AlN/GaN-based high electron mobility transistors. The model consists of coupling both Poisson–Schrödinger and direct tunneling equations to calculate the forward gate current through the gate stack in one dimension. The model results are compared with experimental data at 300 and 425 K. To accurately reproduce the experimental behavior at both temperatures, the presence of residual Ga in the AlN layer must be assumed. Further analysis also confirms that for such structures, thermionic emission is negligible compared to the tunneling current, as most current-contributing electrons exhibit energy lower than the AlN-spacer barrier height. The temperature dependency of the forward gate current arises from the Fermi–Dirac distribution, resulting in a strong forward gate current temperature dependency at low voltages. Finally, additional investigations demonstrate that the forward gate current is mainly driven by the AlN-spacer thickness and the eventual Ga contamination, while the AlGaN layer properties have a less significant impact. Thus, the AlN-spacer fabrication constitutes a crucial technological step not only to increase electron mobility but also to ensure a low forward gate current.