On-state breakdown in power HEMT's: Measurements and modeling

We have carried out a systematic study of on-state breakdown in a sample se t of InAlAs/InGaAs HEMT's using a new gate current extraction technique in conjunction with sidegate and temperature-dependent measurements. We find t hat as the device is turned on, the breakdown voltage limiting mechanism ch anges from a TFE-dominated process to a multiplication-dominated process. T his physical understanding allows the creation of a phenomenological physic al model for breakdown which agrees well with all our experimental results, and explains the relationship between BVon, and the sheet carrier concentr ation. Our results suggest that depending on device design, either on-state or off-state breakdown can limit maximum power.