High-performance enhancement-mode AlGaN/GaN HEMTs using fluoride-based plasma treatment

We report a novel approach in fabricating high-performance enhancement mode (E-mode) AlGaN/GaN HEMTs. The fabrication technique is based on fluoride-based plasma treatment of the gate region in AlGaN/GaN HEMTs and post-gate rapid thermal annealing with an annealing temperature lower than 500 degrees C. Starting with a conventional depletion-mode HEMT sample, we found that fluoride-based plasma treatment can effectively shift the threshold voltage from.- 4.0 to 0.9 V. Most importantly, a zero transconductance (g(m)) was obtained at V-gs = 0 V, demonstrating for the first time true E-mode operation in an AlGaN/GaN HEMT. At V-gs = 0 V, the off-state drain leakage current is 28 mu A/mm at a drain-source bias of 6 V. The fabricated E-mode AlGaN/GaN HEMTs with 1 mu m-long gate exhibit a maximum drain current density of 310 mA/mm, a peak g(m) of 148 mS/mm, a current gain cutoff frequency f(T) of 10.1 GHz and a maximum oscillation frequency f(max) of 34.3 GHz.