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

We report on the MOCVD growth of smooth (010) (AlxGa1-x)(2)O-3 and (100) (AlyGa1-y)(2)O-3 epitaxial films on beta-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)(2)O-3 layers and estimate the Al composition. The incorporation efficiency of Al into the (AlGa)(2)O-3 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)(2)O-3 films with a record high Al composition of x = 30% for a film grown on a (010) beta-Ga2O3 substrate and with an Al composition of up to y = 45% on the (100) beta-Ga2O3 substrate was realized by introducing similar to 18% Al mole fraction into the reactor. N2O grown beta-(AlGa)(2)O-3/beta-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 gamma-phase (AlxGa1-x)(2)O-3 is grown on (010) beta-Ga2O3 substrates. In contrast, on the (100) beta-Ga2O3 substrate, the (AlyGa1-y)(2)O-3 layers are beta-phase, but with two separate Al compositions owing to the local Al segregation. The nitrogen doping of (010) beta-(AlxGa1-x)(2)O-3 with [N] ranging 6 x 10(17)-2 x 10(19) 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 beta-(AlGa)(2)O-3, which paves the way for the realization of efficient power devices, such as modulation-doped field effect transistors.