0.2-μm AlGaN/GaN High Electron-Mobility Transistors With Atomic Layer Deposition Al2O3 Passivation

We report a successful application of atomic layer deposition (ALD) aluminum oxide as a passivation layer to gallium nitride high electron-mobility transistors (HEMTs). This new passivation process results in 8%-10% higher dc maximum drain current and maximum extrinsic transconductance, about one order of magnitude lower drain current in the subthreshold region, 10%-20% higher pulsed-IV drain current, and 27%-30% higher RF power with simultaneously 5-8 percentage point higher power-added efficiency. The achieved improvement in device performance is attributed to the outstanding quality of the interface between III-N and the ALD aluminum oxide resulting from the uniqueness of the adopted ALD process, featuring a wet-chemical-based wafer preparation as well as a pregrowth self-cleaning procedure in the growth chamber. This technology can be readily integrated into the HEMT-based integrated circuit fabrication process, making the ALD aluminum oxide-passivated GaN HEMTs excellent candidates for multiple microwave and millimeter-wave power applications.