Compensation Dopant-Free GaN-on-Si HEMTs With a Polarization Engineered Buffer for RF Applications

We report on the performance of compensation doping-free aluminum gallium-nitride (AlGaN)/gallium-nitride (GaN) high-electron mobility transistors (HEMTs) realized using a polarization-graded buffer scheme on Silicon for RF applications. We use a compositionally reverse-graded AlGaN (g-AlGaN) layer to engineer a resistive buffer, which in addition to acting as a back-barrier, circumvent the need for compensation dopants such as Fe or C. As a proof of concept, we have demonstrated transistors with0.35~μ mgate length and source-connected field plates. Devices exhibit a maximum drain current of 1 A/mm and OFF-state breakdown voltage of 144 V. Gate- and drain-lag pulsedI–Vmeasurements show very low-current collapse (CC) indicating minimal buffer- and surface-trapping. Further evidence from substrate ramp characterization shows positive charge storage in the buffer, indicating a reduced buffer back-gating effect under dynamic conditions. RF performance of HEMTs on these polarization-graded buffers is reported with a peakfₜ/fₘₐₓof 49.2/86.4 GHz. Load-pull measurements at 10 GHz yielded an output power of 1.45 W/mm with a power-added efficiency (PAE) of 11%.