Degradation of AlGaN/GaN HEMTs under elevated temperature lifetesting

Elevated temperature lifetesting was performed on 0.25 mum AlGaN/GaN HEMTs grown by MOCVD on 2-in. SiC substrates. A temperature step stress (starting at T(a) of 150 degreesC with a step of 15 degreesC; ending at T(a) of 240 degreesC; 48 h for each temperature cycle) was employed for the quick reliability evaluation of AlGaN/GaN HEMTs. It was found that the degradation of AlGaN/GaN HEMTs was initiated at ambient temperature of 195 degreesC. The degradation characteristics consist of a decrease of drain current and transconductance, and an increase of channel-on-resistance. However, there is no noticeable degradation of the gate diode (ideality factor, barrier height, and reverse gate leakage current). The FIB/STEM technique was used to examine the degraded devices. There is no detectable ohmic metal or gate metal interdiffusion into the epitaxial materials. Accordingly, the degradation mechanism of AlGaN/GaN HEMTs under elevated temperature lifetesting differs from that observed in GaAs and/or InP HEMTs. The reliability performance was also compared between two vendors of AlGaN/GaN epilayers. The results indicate that the reliability performance of AlGaN/GaN HEMTs could strongly depend on the material quality of AlGaN/GaN epitaxial layers on SiC substrates. (C) 2004 Elsevier Ltd. All rights reserved.