Analysis of threshold voltage instability in AlGaN/GaN MISHEMTs by forward gate voltage stress pulses

We report on the investigation of theV_thdrift behaviour of AlGaN/GaN MISHEMTs upon forward gate voltage stress in dependence of stress bias and stress time. The pulsed measurements allow for the evaluation of the operational regime for optimum device efficiency. We compared the effect of two different high‐κgate dielectric materials with similar equivalent oxide thicknessϵ₀ϵ_r/t_high‐κon theV_thinstability in order to separate the influence of the heterojunction design and the high‐κ/GaN‐cap interface from the bulk high‐κ. The matched gate capacitance coupling of the studied Al₂O₃and HfO₂gate dielectric results in an nearly identical critical forward gate voltage, where the AlGaN barrier potential is lowered and severe threshold voltage shift (ΔV_th) into the positive voltage direction is induced. Beyond this critical forward voltage, detailed time‐dependent stress pulse measurements from 1 µs to 1000 s revealed an immediate electron injection and trapping at the oxide/GaN interface for stress pulses witht_stress ≥ 1 µs. The presented results ofV_thdrift analysis demonstrate the limits of the maximum tolerable forward gate voltage of the investigated Al₂O₃and HfO₂MISHEMTs, although the excellent low‐leakage currents of the insulated gate would imply a potentially higher gate‐overdrive.