New electrical overstress and energy loss mechanisms in GaN cascodes

Depletion-mode Gallium Nitride Field-Effect Transistors (d-mode GaN FETs) need to be cascoded with a low-voltage enhancement-mode (e-mode) Si FET in order to satisfy the safety requirements of the power electronics industry. We find that the standard GaN cascoded structure is susceptible to electrical overstress and additional energy loss mechanisms. This paper provides an understanding of these mechanisms and their effects on both electrical overstress and energy loss. It also provides a method to measure the loss, and presents a benchmarking figure-of-merit. The insights will also be relevant for other wide-bandgap depletion-mode cascoded solutions e.g. SiC JFET, and are important for the successful design of cascoded solutions.