Comprehensive Study of the Complex Dynamics of Forward Bias-Induced Threshold Voltage Drifts in GaN Based MIS-HEMTs by Stress/Recovery Experiments

The transient recovery characteristics of the threshold voltage drift (ΔV_th) of GaN-based HEMTs with a SiO₂ gate dielectric induced by forward gate bias stress are systematically and comprehensively investigated for stress times from 100 ns to 10 ks, recovery times from 4 μs to 10 ks, and stress biases from 1 to 7 V. The measured recovery data are analyzed using the concept of capture emission time maps. It is shown that the observed data cannot be explained by simple first-order defect kinetics. It is revealed that the recovery curves for constant stress times scale with the stress bias. Furthermore, the shape of the recovery curves changes from concave to convex with increasing stress time, independent of the stress bias. For short stress times and low stress bias, a dominant rate limiting effect of the III/N barrier layer is proposed. Defect-related physical processes with a broad distribution of characteristic time constants are discussed to explain the logarithmic time dependency of ΔV_th stress and recovery, at which the role of the Coulomb feedback effect, complex defects, and spatially distributed defects are considered.