Steep Sub-Boltzmann Switching in AlGaN/GaN Phase-FETs With ALD VO2

We report the first demonstration of ultralow leakage AlGaN/GaN MOS-HEMTs on silicon substrates loaded at the source with atomic layer deposition (ALD)grown VO
₂
metal-insulator transition (MIT) material resistors. The resulting GaN phase-transition FET (phase-FET) shows steep sub-Boltzmann switching in its transfer characteristics in both sweep directions with slopes of ~9.9 and ~28.2 mV/decade at 60 °C. The control MOS-HEMTs and the phase-FETs show more than 12-order on/off ratio with ultralow off-state leakage. Because of the MIT, the drain current and the transconductance also show unconventional behavior. This first demonstration of ultralow leakage steep switching in GaN phase-FETs using integrationfriendly ALD VO
₂
opens the door to introducing new functionalities in nitride low-power digital devices, microwave circuits, photonic devices, and power electronics in the GaN-on-silicon platform.