Buried channel normally-off AlGaN/GaN MOS-HEMT with a p-n junction in GaN buffer

A buried channel normally-off AlGaN/GaN MOS-HEMT with gate recess etching is reported. The buried channel operation is achieved by in situ doping of GaN to introduce a p-n junction in the GaN buffer. The fabricated buried channel MOS-HEMT with 12.5 nm atomic layer deposition (ALD) Al₂O₃ gate dielectric featured a threshold voltage of 1.3 V with a drain saturation current of 287 mA mm⁻¹ for a device with 3.5 μm long gate length and 11 μm source-drain spacing. The field effect mobility improved from 25 cm²/Vs for a reference device to 142 cm²/Vs for the buried channel device. Due to the presence of the p-n junction depletion region in the GaN buffer, the leakage in the off state decreased by about 4 orders of magnitude (4 nA mm⁻¹ compared to 76 uA mm⁻¹ for the reference device). The buried channel device also gives better breakdown characteristics, with a breakdown voltage of 158 V compared to 98 V for the reference device. (paper)