Low Subthreshold Swing Double-Gate $\beta$ -Ga2O3 Field-Effect Transistors With Polycrystalline Hafnium Oxide Dielectrics

We demonstrate low subthreshold swing (SS) double-gate (DG) β-Ga₂O₃ field-effect transistors (FETs) with polycrystalline hafnium oxide (HfO2) gate dielectrics. The atomic layer deposited HfO₂ layer at an elevated temperature of 350 °C without post-deposition annealing has a polycrystalline structure. The threshold voltage is modulated from depletionto enhancement-mode by independently controlled bottom-gate bias. The SS is reduced to as low as 64 mV/dec with mobility of 20 cm²/V·s while maintaining a high ON/OFF ratio of 10⁷ and negligible hysteresis of 30 mV via double-gate operation. The device shows an ON/OFF ratio of 10₆ and the SS of 320 mV/dec up to an operating temperature of 250 °C and the OFF-state breakdown voltage of 355 V. The demonstrated DG β-Ga₂O₃ FETs with the polycrystalline HfO₂ layer is a promising structure for energy efficient high temperature device and circuit applications.