Dielectric Engineering of HfO2 Gate Stacks Towards Normally-ON and Normally-OFF GaN HEMTs on Silicon

TL;DR

This study investigates HfO2 gate dielectrics on GaN-based transistors, revealing key electronic properties, interface traps, and device performance metrics for normally-ON and normally-OFF GaN HEMTs on silicon.

Contribution

It provides detailed analysis of HfO2/GaN interfaces, including conduction band offset, trap densities, and device characteristics, advancing the understanding of dielectric engineering for GaN transistors.

Findings

Conduction band offset of 1.9 eV for HfO2/GaN.

Normal-ON HfO2/AlGaN/GaN MISHEMTs show negligible threshold voltage shifts.

Transconductance of 110 mS/mm for 3 μm gate length devices.

Abstract

We report on the interfacial electronic properties of HfO2 gate dielectrics both, with GaN towards normally-OFF recessed HEMT architectures and the AlGaN barrier for normally-ON AlGaN/GaN MISHEMTs for GaN device platforms 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. Conductance measurements on HfO2/GaN MOSCAPs reveal an interface trap state continuum with a density of 9.37x1012 eV-1cm-2 centered at 0.48 eV below EC. The forward and reverse current densities are shown to be governed by Fowler-Nordheim tunneling and Poole-Frenkel emission respectively. Normally-ON HfO2/AlGaN/GaN MISHEMTs exhibit negligible shifts in threshold voltage, transconductances of 110mS/mm for 3 {\mu}m gate length devices, and three-terminal OFF-state gate leakage currents of 20 nA/mm at a VD of 100 V. Dynamic capacitance dispersion measurements show two peaks at the AlGaN/GaN interface corresponding to slow and fast interface traps with a peak Dit of 5.5x1013 eV-1cm-2 and 1.5x1013 eV-1cm-2 at trap levels 0.55 eV and 0.46 eV below EC respectively. The HfO2/AlGaN interface exhibits a peak Dit of 4.4x1013 eV-1cm- 2 at 0.45 eV below EC.