GaN cap impacts on gate leakage mechanisms in AlGaN/GaN high-electron mobility transistors

Abstract

In this Letter, the impacts of the GaN cap on the gate leakage mechanisms have been investigated in the recessed-gate AlGaN/GaN high-electron-mobility transistors. The recessed gate with GaN cap removal under the gate can be a way to shrink the gate-to-channel distance, therefore improving the current density and the transconductance without sacrificing the interface properties, which play an important role in current collapse. The investigation of gate leakage current, as a reliability issue, on the recessed gate with GaN cap removal is, therefore, important. From the Igs–Vgs measurements at different temperature and stress conditions, it is found that the leakage mechanisms of the recessed-gate devices with cap removal are identical to those of the standard devices. However, the trap energy level is higher when extracted from the two-step trap-assisted tunneling mechanism at high reverse gate bias, resulting in higher leakage current for the recessed-gate device. Besides, stress measurements on the device reveal that the leakage mechanism at low reverse gate bias changes from temperature-independent before stress to temperature-dependent after stress. It is also found that a recoverable trap with a new energy level is generated after stress based on temperature-sensitive characteristics, which corresponds to the Poole–Frenkel emission mechanism.