Atomic-scale oxygen engineering as a switching strategy for 2DEG: Evolution from p-GaN to GaON enabling non-destructive HEMT fabrication

The unclear atomic-scale evolution and passivation mechanism of oxygen engineering for gallium nitride (GaN) and GaN-based devices currently limit the application of this promising strategy. Hiring the oxygen engineering to fabricate the p-GaN gate high-electron-mobility transistors (HEMTs), this work converts the p-GaN cap access region into GaON as a switching strategy for two-dimensional electron gas (2DEG) via oxygen plasma treatment (OPT) and rapid thermal annealing (RTA). The process fully recovers the 2DEG in the AlGaN/GaN heterojunction, resulting in an Enhancement-Mode (E-mode) HEMT fabricated without any etching step. The atomic-scale evolution of oxygen and the corresponding recovery mechanism of the 2DEG have been systematically investigated. The OPT process introduces sufficient oxygen atoms to form a metastable GaON layer containing abundant interstitial oxygen (O_i) which acts as an acceptor and limits 2DEG recovery. Subsequent RTA converts most O_i into lattice oxygen (O_L), forming a thermodynamically stable GaON layer. The GaON layer elevates the Fermi level of the AlGaN/GaN heterojunction, while the enhanced O_L compensates for the p-GaN acceptors. This process fully restores the 2DEG at the underlying interface. By providing atomic-scale insight into the evolution of oxygen in GaN, this work contributes a promising strategy to advance unique materials for emerging electronics and optoelectronics.