Recessed gate AlGaN/GaN MODFET on sapphire grown by MOCVD

A recessed gate AlGaN/GaN modulation-doped field-effect transistor (MODFET) has been grown on a sapphire substrate by metalorganic chemical vapor deposition (MOCVD). Two-dimensional electron gas (2DEG) mobility and sheet carrier density of AlGaN/GaN heterostructure on the sapphire substrate were 740 cm/sup 2//V/spl middot/s and 5.1/spl times/10/sup 12/ cm/sup -2/ at 300 K, and 12000 cm/sup 2//V/spl middot/s and 2.8/spl times/10/sup 12/ cm/sup -2/ at 8.9 K, respectively. The recessed gate device showed the maximum extrinsic transconductance 146 mS/mm and drain-source current 900 mA/mm for the AlGaN/GaN MODFET with a gate length Lg of 2.1 /spl mu/m at 25/spl deg/C. At an elevated temperature of 350/spl deg/C, the maximum extrinsic transconductance and drain-source current were 62 mS/mm and 347 mA/mm, respectively. The AlGaN/GaN MODFET exhibited the stable operation with good pinch-off characteristics at high temperatures, and the very weak temperature dependence of the threshold voltage. The drain current collapse was not observed in the dark and AC measurement.