Study of Vₜₕ Instability During Recovery After Off-State Stress in p-GaN HEMT

In this study, the threshold voltage ( ${\mathrm{V}}_{\mathbf {\text {th}}}$ ) instability subjected to off-state stress (OSS) in p-GaN gate AlGaN/GaN high-electron-mobility transistors (HEMTs) is investigated. During stress, ${\mathrm{V}}_{\mathbf {\text {th}}}$ exhibits a slight positive shift; however, a more pronounced positive shift occurs within the first 5 seconds of the recovery phase. The evolution of gate leakage current ( ${\mathrm{I}}_{\mathbf {\text {g}}}$ ) under off-state stress is also analyzed. A physical model is proposed to explain the instability, incorporating trap-assisted thermionic field emission (TA-TFE) at the GaN layer and gate electron injection, with holes and electrons trapped in defects in the GaN layer and AlGaN barrier, respectively. Dynamic on-state resistance ( ${\mathrm{R}}_{\mathbf {\text {on}}}$ ) measurements are employed to further investigate the current collapse effect. By monitoring dynamic on-state resistance at temperatures ranging from 30 to 90°C, the activation energies of the responsible defects are extracted, identified as nitrogen vacancy in AlGaN barrier and carbon impurity substituting for nitrogen in GaN layer, thus validating the proposed model.