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We developed a high-quality plasma enhanced atomic layer deposited (PEALD) aluminum oxynitride (AlO x N y ) process for the metal-oxide-semiconductor (MOS) gate insulator of fully-recessed-gate AlGaN/GaN-on-Si MOS-heterojunction field-effect transistors (MOS-HFETs). It was found that the cyclic nitrogen incorporation into aluminum oxide (Al 2 O 3 ) during PEALD process improved the conduction band offset at GaN interface resulting in higher forward breakdown field strength, which also contributed to suppressed trapping effects under forward gate bias stress. Improved interface characteristics, which resulted from suppressed surface oxidation, led to significant improvement of threshold voltage stability. A low threshold voltage hysteresis of 180 mV at maximum gate sweep voltage of 10 V was obtained with AlO x N y gate insulator. The MOS channel mobility was also improved to 235 cm 2 V −1 s −1 . The fabricated fully-recessed-gate AlGaN/GaN-on-Si MOS-HFET with PEALD AlO x N y gate insulator exhibited excellent overall performances such as a threshold voltage of 3.2 V, a maximum drain current density of 481 mA mm −1 , an on/off current ratio of ∼10 10 , an ON-resistance of 12 mΩ mm, and a breakdown voltage of 1050 V.

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