Impacts of $n$-GaN Doping Concentration on Gate Reliability of $p-n$ Junction/AlGaN/GaN HEMTs

In this work, the $p-n$ junction (PNJ)/AlGaN/GaN HEMTs with different effective $n$-GaN doping concentrations ($N_{\mathrm{D}}$) of $1.7\times 10^{20}$ cm⁻³, $2.6\times 10^{19}$ cm⁻³ and $1\times 10^{17}$ cm⁻³ are comparatively studied to reveal the impacts of $N_{\mathrm{D}}$ on gate reliability. With lower $N_{\mathrm{D}}$, gate leakage reduces, and forward gate breakdown voltage boosts up to 18.6 V, whereas the maximum applicable gate voltage for a 10-year lifetime will not continually increase when $N_{\mathrm{D}}$ decreases to $1\times 10^{17}$ cm⁻³. This feature is attributed to premature breakdown caused by electric-field crowding at the surface of the fully depleted n-GaN. To fully exploit the reliability of the PNJ-HEMTs, it is suggested that the $N_{\mathrm{D}}$ of PNJ-HEMTs should be carefully designed to widen the depletion region in $p-n$ junction appropriately, while premature breakdown caused by electric-field crowding at the surface should be avoided.