Dielectric Engineering of HfO 2 Gate-Stacks for Normally-ON GaN HEMTs on 200-mm Silicon Substrates

We report on the band offset and interfacial electronic properties of e-beam evaporated HfO2gate dielectrics on III-nitride device stacks on Si. A conduction band offset of 1.9 eV is extracted for HfO2/GaN along with a very low density of fixed bulk and interfacial charges for optimally annealed samples. Normally-ON HfO2/AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors exhibit negligible shifts in threshold voltage, transconductances of 120 mS/mm for 3-μm gate length devices, and three-terminal off-state gate leakage currents of 55 nA/mm at a VDof 100 V. Dynamic capacitance dispersion measurements in the temperature range of 25 °C-200 °C show two peaks at the AlGaN/GaN interface corresponding to slow and fast interface traps with a peak Ditof 5.5 × 1013and 1.5 × 1013eV-1cm-2respectively as a function of Fermi level position above EC. The HfO2/AlGaN interface exhibits a reasonably constant peak Ditof 2 × 1013-4.4 × 1013eV-1cm-2at trap levels of 0.42-0.72 eV below EC. Hysteretic pulsed ID-VG measurements revealed a negative shift in threshold voltages indicative of unoccupied donor-like trap states at the HfO2/AlGaN interface and comparable Ditto that inferred from conductance measurements.