Characterizations of recessed gate AlGaN/GaN HEMTs on sapphire

A recessed gate high electron mobility transistor (HEMT) has been fabricated with AlGaN/GaN heterostructure on a sapphire substrate using metalorganic chemical vapor deposition. Capacitance-voltage (C-V) and Shubnikov-de Haas measurements have shown the formation of two-dimensional (2-D) electron gas (2DEG) at Al/sub 0.11/Ga/sub 0.89/N/GaN heterointerface. A 2DEG mobility 12000 cm/sup 2//V-s with a sheet carrier density 2.8/spl times/10/sup 12/ cm/sup -2/ was measured on Al/sub 0.11/Ga/sub 0.89/N/GaN heterostructure at 8.9 K. The recessed gate Al/sub 0.26/Ga/sub 0.74/N/GaN HEMT structure showed maximum extrinsic transconductance 181 mS/mm and drain-source current 1120 mA/mm for a gate length 1.5 /spl mu/m at 25/spl deg/C. The device exhibited stable operation characteristics at 350/spl deg/C for long time (500 h). No interfacial change has been observed at metal/AlGaN interface even after 350/spl deg/C for 500 h treatment. The threshold voltage of device does not depend very much on operating temperature (25 to 350/spl deg/C).