N₂O grown high Al composition nitrogen doped β-(AlGa)₂O₃/β-Ga₂O₃ using MOCVD

We report on the MOCVD growth of smooth (010) (Al_xGa_1–x)₂O₃ and (100) (Al_yGa_1–y)₂O₃ epitaxial films on β-Ga₂O₃ substrates with (010) and (100) orientations, respectively, using N₂O for oxidation. High resolution x-ray diffraction was used to evaluate the phase purity and strain characteristics of the (AlGa)₂O₃ layers and estimate the Al composition. The incorporation efficiency of Al into the (AlGa)₂O₃ films depends on process conditions, including chamber pressure, growth temperature, and gas phase Al concentration. Layers grown at lower reactor pressure and substrate temperature and higher gas phase Al concentration showed higher Al incorporation. Pure beta phase (AlGa)₂O₃ films with a record high Al composition of x = 30% for a film grown on a (010) β-Ga₂O₃ substrate and with an Al composition of up to y = 45% on the (100) β-Ga₂O₃ substrate was realized by introducing ∼18% Al mole fraction into the reactor. N₂O grown β-(AlGa)₂O₃/β-Ga₂O₃ superlattice structures with an Al composition of 5% were also demonstrated on both substrate orientations. When higher gas phase Al concentration is introduced into the reactor, pure γ-phase (Al_xGa_1–x)₂O₃ is grown on (010) β-Ga₂O₃ substrates. In contrast, on the (100) β-Ga₂O₃ substrate, the (Al_yGa_1–y)₂O₃ layers are β-phase, but with two separate Al compositions owing to the local Al segregation. The nitrogen doping of (010) β-(Al_xGa_1–x)₂O₃ with [N] ranging 6 × 10¹⁷–2 × 10¹⁹ cm⁻³ was achieved using N₂O. Higher Al composition and lower substrate temperature lead to higher N incorporation. The results show that using N₂O as an oxygen source can lead to the growth of high Al content β-(AlGa)₂O₃, which paves the way for the realization of efficient power devices, such as modulation-doped field effect transistors.