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_0.11Ga_0.89N/GaN heterointerface. A 2DEG mobility 12 000 cm²/V-s with a sheet carrier density 2.8 × 10¹² cm^-2 was measured on Al_0.11Ga_0.89N/GaN heterostructure at 8.9K. The recessed gate Al_0.26Ga_0.74N/GaN HEMT structure showed maximum extrinsic transconductance 181 mS/mm and drain-source current 1120 mA/mm for a gate length 1.5 μm at 25°C. The device exhibited stable operation characteristics at 350°C for long time (500 h). No interfacial change has been observed at metal/AlGaN interface even after 350 °C for 500 h treatment. The threshold voltage of device does not depend very much on operating temperature (25 to 350°C).