Floating body effects in carbon doped GaN HEMTs

Abstract

GaN power HEMTs use carbon doped buffers to deliver high breakdown voltage and off-state low leakage; however these devices are highly vulnerable to dynamic dispersion. Carbon doped GaN has its Fermi level pinned 0.9eV above the valence band and in equilibrium would be isolated from the 2DEG by a reverse biased PN junction and hence would be electrically floating. In reality leakage across that junction and charge storage in the compensated deep acceptors controls the buffer potential, the dynamic on-resistance dispersion and the gate-drain breakdown voltage. We discuss experiment and simulation that supports the model that controlling leakage to the floating buffer is critical for power device operation.