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Self-heating effects and temperature rise in AlGaN/GaN HEMTs grown on silicon and sapphire substrates are studied, exploiting transistor dc characterization methods. A negative differential output resistance is observed for high dissipated power levels. An analytical formula for a source-drain current drop as a function of parasitic source resistance and threshold voltage changes is proposed to explain this behavior. The transistor source resistance and threshold voltage is determined experimentally at different elevated temperatures to construct channel temperature versus dissipated power transfer characteristic. It is found that the HEMT channel temperature increases rapidly with dissipated power and at 6 W/mm reaches values of 320 C for sapphire and 95 C for silicon substrate, respectively.

An analytical model for threshold voltage calculation for metal-oxide-semiconductor GaN based high electron mobility transistors is proposed. This model includes polarization induced charges at each heterostructure interface/surface, surface donors, oxide/barrier interface traps charge, and interfacial and bulk fixed oxide charge. Applicability of the model is demonstrated on GaN/AlGaN/GaN MOS heterostructure capacitors with Al2O3 and HfO2 gate dielectrics grown by atomic layer deposition with different barrier surface treatment and Al2O3 thicknesse.