Normally-off AlGaN/GaN recessed MOS-HEMTs on normally-on epitaxial structures for microwave power applications

摘要

This paper presents the realization and characterization of normally-off recessed MOS-HEMTs on a Ka-band-dedicated AlGaN/GaN epitaxial structure. Previous HEMTs results on this structure feature an output power of 3.5 W/mm with PAE of 39 % at 30 GHz CW. Normally-off operation was achieved through the use of gate recess combined with a Al2O3 gate oxide, by a fabrication process compatible with that of normallyon high-frequency power HEMTs. Electrical performances include threshold voltage over 1 V, pulsed drain current in excess of 400 mA/mm and fmax of 35 GHz. Dynamic Ron transients after switching events were investigated, showing thermally-activated increase of Ron over 10 decades of time. Low-frequency output-admittance measurements were also conducted to evaluate the impact of gate recess etching on charge trapping behavior.