Impact of Inadequate Mg Activation on Dynamic Threshold Voltage of Schottky-type $p$-GaN Gate HEMTs

To further reduce the forward gate current of Schottky-type $p$-GaN gate HEMTs, inadequate Mg activation in $p$-GaN is deployed in this work, which tends to convert the conventional $p$-GaN into insulating GaN with high concentration of Mg passivated by hydrogens. The free hole concentration in $p$-GaN is reduced, and so is the hole deficiency effect that is the main cause of dynamic threshold voltage ($V_{\text{TH}}$) in commercial Schottky-type $p$-GaN gate HEMTs. However, plenty of electron traps left in $p$-GaN lead to more significant dynamic $V_{\text{TH}}$ shift (up to 6 V) under reverse gate bias ($V_{\text{GSQ}}$, up to -13 V), as revealed by the $V_{\text{TH}}$ recovery processes under different conditions of light illumination and forward gate bias. Fortunately, under forward $V_{\text{GSQ}}$, the fully depleted $p$-GaN layer facilitates electron acceleration by the electric field, suppressing the electron trapping and consequent dynamic $V_{\text{TH}}$ shift. Besides, deeper-level electron trapping in AlGaN may account for the slight dynamic $V_{\text{TH}}$ shift under $V_{\text{GSQ}}\geq 7\mathrm{V}$.