Substrate Bias Enhanced Trap Effects on Time-Dependent Dielectric Breakdown of GaN MIS-HEMTs

In this work, we present the substrate bias enhanced trap effects on time-dependent dielectric breakdown (TDDB) in GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) by experiment. Under different substrate biases, the shape parameter β and scale factor η of the Weibull distribution are extracted from the experimental data. A monotonical decrease in β from intrinsic breakdown to extrinsic breakdown relating to the hole-emission from the acceptor-like buffer traps with increased negative substrate biases has been observed, while η is increased at large positive substrate biases. This unexpected increase in η suggests that the donor-like buffer traps play an important role with a longer lifetime. The trap mechanisms, relating to percolation path establishment, are analyzed based on progressive breakdown (PBD). The capacitance-voltage characteristics are measured during each stress cycle confirming the hole fluence and electron injection in the gate-stack layer with different trap distributions under various substrate biases. Finally, 2-D device simulations are carried out to probe for physical insight into the traps on TDDB failure mechanisms.