Investigation of self-heating effects in AlGaN-GaN HEMTs

Self-heating effects in AlGaN-GaN HEMTs grown on sapphire are studied exploiting transistor DC characterization methods. A negative differential output resistance is observed for high power levels accompanied by a transistor transconductance decrease. An analytical formula for a source-drain current drop as a function of a parasitic source resistance is proposed to explain this behavior. The transistor source resistance is determined experimentally at different elevated temperatures to construct channel temperature vs. dissipated power transfer characteristics. It is found that the HEMT channel temperature increases rapidly with dissipated power and reaches values of /spl sim/200/spl deg/C at 2.6 W/mm. The transistor thermal impedance was determined to be 67/spl deg/CmmW/sup -1/.