High Temperature Operation of E-Mode and D-Mode AlGaN/GaN MIS-HEMTs With Recessed Gates

High temperature operation of enhancement-mode (E-mode) and depletion-mode (D-mode) AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) was demonstrated. By using the circular device structure, off-state current was effectively suppressed, and record high Ion/Ioff ratio around 108 was obtained at 400 °C. Atomic layer etching was used for formation of the gate recess structure in the E-mode device, and good interface was made which enabled stable normally-off operation up to 400 °C. D-mode device experienced positive threshold voltage shift during the high temperature operation and after cooling down to room temperature, due to strain relaxation. On the other hand, due to the very thin AlGaN layer retained under the gate of the E-mode device, the threshold voltage of the E-mode device is nearly unchanged when the sample is heated up and cooled down. A direct coupled field-effect transistor logic (DCFL) inverter was fabricated based on the E-mode and D-mode devices and showed stable operation up to 400 °C.