Understanding Forward and Reverse Overcurrent-Induced Electrical Parameter Degradations of Cascode GaN HEMTs

In this work, the degradations of electrical parameters of GaN-based high electron mobility transistors in Cascode structure (Cascode GaN HEMTs) induced by forward and reverse overcurrent stress are comparatively investigated. Based on an innovative test platform, on-state resistance degradations have been in-situ observed immediately after overcurrent stresses in both forward and reverse directions simultaneously. Furthermore, the similarities and distinctions in degradation effects caused by stresses have been demonstrated through the repetitive on-board test strategy. More severe degradation of on-state resistance has been observed under overcurrent stress in reverse conduction compared to forward conduction. With the help of TCAD simulations, the positive substrate voltage induced by reverse overcurrent has been verified to cause partial channel electrons to inject into the buffer layer. The injected electrons are subsequently captured by intrinsic traps leading to more pronounced on-resistance degradation, which is validated by C-V characterizations.