Normally-off AlGaN/GaN MOS-HEMTs by KOH wet etch and rf-sputtered HfO2 gate insulator

Normally-off AlGaN/GaN MOS HEMTs were successfully fabricated and investigated by simple KOH wet etch and rf-sputtered HfO₂ as a gate insulator. The proposed KOH wet etch resulted in an adequate recess-depth and smooth etched surface. The gate-recessed HEMT exhibits threshold voltage (V_th) shifts from -3 to 1.5 V after 150 s KOH-wet etch. The breakdown voltage of 1580 V and R_{on, sp} of 8.09 mΩ·cm² was measured in the AlGaN/GaN HEMT with the gate-drain distance of 20 μm-long. The high FOM (figure of merit) of 308 MW/cm² was achieved. Our experimental results indicate that the proposed simple KOH wet etching and rf sputtered HfO₂-gate insulator may be promising for the normally-off AlGaN/GaN MOS HEMTs fabrication.