Impact of carbon in the buffer on power switching GaN-on-Si and RF GaN-on-SiC HEMTs

This article addresses the impact of the buffer doping on the critical performance issues of current-collapse and dynamic R_ON in GaN high electron mobility transistors. It focusses on the effect of carbon, either incorporated deliberately in GaN-on-Si power switches, or as a background impurity in iron doped RF GaN-on-SiC devices. The commonality is that carbon results in the epitaxial buffer becoming p-type and hence electrically isolated from the two-dimensional electron gas by a P-N junction. Simulations which incorporate a model for leakage along dislocations are used to show that a remarkably wide range of experimental observations can be explained including dynamic R_ON and the complex time dependence of drain current transients in power switches. In RF GaN-on-SiC devices, the current-collapse, the drain current dynamics, kink effect, pulse-IV and electric field distribution in the gate-drain gap can all be explained.