Negative capacitance overcomes Schottky-gate limits in GaN high-electron-mobility transistors

For high-electron-mobility transistors based on two-dimensional electron gas (2DEG) within a quantum well-such as those based on AlGaN/GaN heterostructures-a Schottky gate is used to maximize the amount of charge that can be induced and thereby the current that can be achieved. However, the Schottky gate also leads to very high leakage current through the gate electrode. Adding a conventional dielectric layer between the nitride layers and gate metal can reduce leakage; but this comes at the price of a reduced drain current. We used a ferroic HfO₂- ZrO₂ bilayer as the gate dielectric and achieved a simultaneous increase in the ON current and decrease in the leakage current, a combination otherwise not attainable with conventional dielectrics. This approach surpasses the conventional limits of Schottky GaN transistors and provides a new pathway for improved performance in transistors based on 2DEG.