The superior material properties give GaN heterostructure based HEMT devices a unique stability, reliability, and robustness for their use in extreme environments. The trap related issues due to inherent defects in the material system pose threat to the stable and reliable operation of the device. While operating the GaN devices (HEMTs) in extreme conditions under the influence of high bias stress, high temperature or radiation exposure can drive them to degradation and lead to catastrophic failure. The effect of applied thermal stress on the gate leakage and off-state drain leakage of inhouse MOCVD grown and fabricated HEMTs have been analyzed. For thermal stress we subject the HEMTs to high temperatures for a sufficiently long time as compared to annealing conditions. It was further ensured that the devices are confined within the elastic limit of degradation, that is, the devices do not undergo breakdown. The gate leakage was modelled using the (phonon assisted tunnelling) PAT and (trap assisted tunnelling) TAT components where, PAT dominated immediately after the thermal stress and a slow recovery (large relaxation time) post stress was attributed to the TAT phenomena. The recovery is suggestive of a partial degradation from the thermal stress although the HEMTs do not come back to its pristine state. A critical temperature of 227C (500 K) was observed to be the onset of degradation from thermal stress. Current deep level transient spectroscopy (C-DLTS) confirms the generation of deep defects from the thermal storage test within the buffer. Raman spectroscopic measurements demonstrated the hot phonon interaction in the GaN buffer which makes the buffer conductive and increases bulk leakage through defect generated paths. Apart from the HEMTs, the impact of thermal storage test at 1000C for 1 hr on different GaN heterostructures were also observed. The material system underwent changes through surface degradation and bulk degradation from the thermal stress.
2025-04-09 09:00:00
