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

Abstract

We report on the MOCVD growth of smooth (010) (AlxGa1–x)2O3 and (100) (AlyGa1–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 (AlxGa1–x)2O3 is grown on (010) β-Ga2O3 substrates. In contrast, on the (100) β-Ga2O3 substrate, the (AlyGa1–y)2O3 layers are β-phase, but with two separate Al compositions owing to the local Al segregation. The nitrogen doping of (010) β-(AlxGa1–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.