Abstract:
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. (structures A). The saturated drain current drops significantly when the temperature rises above room temperature from 300 K to 425 K in both structures A and B. Furthermore, the self-heating effect strongly influences the Ids-Vds characteristics. Especially, the drain current at higher drain voltage becomes weaker and a negative resistance effect may arise. In conclusion, n+GaN/AlInN/GaN HEMTs exhibit better performance, especially when covered with a thin highly-doped capping layer, even when selfheating and thermal effects are taken into account. 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 two-dimensional 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. HEMT’s performances are greatly degraded in by self-heating and thermal effects, more in GaN/Al0.83InN0.17/GaN (structures B) than in GaN/Al0.32Ga0.68N /Ga
