High-VTH E-Mode GaN HEMTs With Robust Gate-Bias-Dependent VTH Stability Enabled by Mg-Doped p-GaN Engineering

Highly stable threshold voltage <inline-formula> <tex-math notation="LaTeX">$({V}_{\text {TH}})$ </tex-math></inline-formula> characteristics are an essential reliability requirement for p -GaN/AlGaN/GaN high-electron-mobility transistors (p-GaN HEMTs) to withstand various gate bias stresses for power applications. In this work, we demonstrate high-<inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> (3.0 V) p-GaN HEMTs with robust <inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> stability by p -GaN gate engineering via Mg doping and activation. The <inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> degradation rates of the resulting device under both pulsed-<inline-formula> <tex-math notation="LaTeX">${I}/{V}$ </tex-math></inline-formula> and bias temperature instability (BTI) stress conditions are less than 10% at high temperatures up to 150°, which is much lower than that of conventional Schottky-type p -GaN HEMTs (20%–30%). Such notable <inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> characteristics are due to the impact ionization (I.I.)-dependent hole compensation under certain gate stress, which effectively alleviates the electron trapping effect and reduces positive <inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> shift. The I.I. occurring in the fully depleted p -GaN layer has been confirmed by both positive temperature-dependent gate breakdown characteristics and numerical simulations. Furthermore, shallow- and deep-level hole traps are identified in the gate-stack of high-<inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> devices by performing the deep-level transient spectroscopy (DLTS) technique. Consequently, the trapping effect associated with hole traps may also alleviate the undesired electron-trapping-induced <inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> shift. These results provide a critical understanding of the <inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> stability of the high-<inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> p -GaN HEMTs (HVT-HEMTs) and important design guidance for commercial device development.