Thermally induced threshold voltage instability of III-Nitride MIS-HEMTs and MOSC-HEMTs: Underlying mechanisms and optimization schemes

The mechanisms of divergent VTH-thermal-stabilities of III-nitride (III-N) MIS-HEMT and MOS-Channel-HEMT are revealed in this work. The more significant VTH-thermal-instability of MIS-HEMT is attributed to the polarized III-N barrier layer that spatially separates the critical gate-dielectric/III-N interface from the channel and allows “deeper” interface trap levels emerging above the Fermi level at pinch-off. We also reveal the influences of the barrier layer's thickness and the fixed charges (e.g. F-) in the barrier layer on VTH-thermal-stability and attempt to provide guidelines for the optimization of insulated-gate III-N power switching devices. A tailor-made normally-off MIS-HEMT with optimal tradeoff between performance and stability is thereby demonstrated, by conjunctively utilizing partially recessed gate and fluorine plasma implantation techniques.