An analytical model for the current voltage characteristics of GaN-capped AlGaN/GaN and AlInN/GaN HEMTs including thermal and self-heating effects

We present an analytical model for the I-V characteristics of AlGaN/GaN and AlInN/GaN high electron mobility transistors (HEMT). Our study focuses on the influence of a GaN capping layer, and of thermal and self-heating effects. Spontaneous and piezoelectric polarizations at Al(Ga,In)N/GaN and GaN/Al(Ga,In)N interfaces have been incorporated in the analysis. Our model permits to fit several published data. Our results indicate that the GaN cap layer reduces the sheet density of the twodimensional electron gas (2DEG), leading to a decrease of the drain current, and that n + -doped GaN cap layer provides a higher sheet density than undoped one. In n + GaN/AlInN/GaN HEMTs, the sheet carrier concentration is higher than in n + GaN/AlGaN/GaN HEMTs, due to the higher spontaneous polarization charge and conduction band discontinuity at the substrate/barrier layer interface