Hf0.5Zr0.5O2-Based Ferroelectric Gate AlGaN/GaN HEMTs With Steep Subthreshold Swings

AlGaN/GaN high-electron-mobility transistors (HEMTs) with Hf0.5Zr0.5O2 (HZO) ferroelectric gates are demonstrated. High-quality HZO ferroelectric thin films with different thicknesses were prepared by plasma-enhanced atomic layer deposition (PEALD) and integrated with HEMTs by introducing Al2O3 interlayers. As the thickness of HZO increases from 6 to 14 nm, the subthreshold swing (SS) first increases and then decreases. Devices with 2 nm Al2O3 interlayer and 6 nm HZO ferroelectric layer exhibit threshold voltage of −4.9 V,
${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$
of 108, and ultralow SS value of 50.2 mV/dec at room temperature, which breaks the theoretical limit of traditional metal-insulator-semiconductor HEMTs (MIS-HEMTs). In addition, the switchable polarization of HZO and the interface/ferroelectric coupling were studied in detail, which has a certain guiding significance for designing and optimizing ferroelectric gate AlGaN/GaN HEMTs in the future.