Recessed-gate enhancement-mode GaN HEMT with high threshold voltage

Fabrication of enhancement-mode high electron mobility transistors (E-HEMTs) on GaN/AlGaN heterostructures grown on SiC substrates is reported. Enhancement-mode operation was achieved with high threshold voltage (VT) through the combination of low-damage and controllable dry gate-recessing and the annealing of the Ni/Au gates. As-recessed E-HEMTs with 1.0 µm gates exhibited a threshold voltage (VT) of 0.35 V, maximum drain current (ID,max) of 505 mA/mm, and maximum transconductance (gm,max) of 345 mS/mm; the corresponding post-gate anneal characteristics were 0.47 V, 455 mA/mm and 310 mS/mm, respectively. The RF performance is unaffected by the post-gate anneal process with a unity current gain cutoff frequency (fT) of 10 GHz.