Improved Lumped Element Model for GaN-based MIS-HEMT gate stack in the spill-over regime

We present an improved method to model the small-signal behaviour of GaN-based metal insulator semiconductor high electron mobility transistor (MIS-HEMT) gate stacks biased in the ‘spill-over’ regime, where electrons accumulate at the ‘critical’ dielectric/III-N interface. In this regime, the small-signal admittance can capture the response of traps at the critical interface up to ~1 eV below the conduction band-edge $(E_{C})$ at elevated temperatures. This allows accurate extraction of the interface trap density $(D_{it})$ which parameterizes the MIS gate stack quality, that in turn strongly influences device functionality and reliability. However, accurate extraction of $D_{it}$ from the small-signal characteristics requires that admittance contributions from interface traps and the intrinsic (i.e. trap-free) gate stack are carefully separated. The lumped element model (LEM) proposed here does this effectively and achieves a better match to experimental measurements than previously reported.