Al_0.7Ga_0.3N MESFET With All-Refractory Metal Process for High Temperature Operation

Ultrawide bandgap Al _0.7 Ga _0.3 N MESFETs with refractory Tungsten Schottky and Ohmic contacts are studied in 300-675 K environments. Variable-temperature dc electrical transport reveals large ON-state drain current densities for an AlGaN device: 209 mA/mm at 300 K and 156 mA/mm at 675 K in the ON-state (25% reduction). Drain and gate currents are only weakly temperature-dependent, suggesting potential for engineering temperature invariant operation. The ON-/ OFF-ratio is limited by OFF-state leakage through the gate, which is attributed to damage from sputter deposition. Future work using refractory metals with larger work functions that are deposited by electron beam deposition is proposed.