(10)-Oriented β-Ga2O3 grown on (0001) sapphire by halide vapor phase epitaxy: growth and structural characterizations

Abstract

In general, β-Ga₂O₃ films with (01) out-of-orientation have been widely obtained and reported on (0001) sapphire substrates by various growth methods. In this paper, the unusual (10)-oriented β-Ga₂O₃ films have been epitaxially grown on (0001) sapphire substrates with high crystal-quality under Ga-rich conditions by halide vapor phase epitaxy (HVPE). The out-of-plane epitaxial relationship as (10) β-Ga₂O₃//(0001) α-Al₂O₃ has been confirmed by XRD and HRTEM analysis. Under most growth conditions, β-Ga₂O₃ films exhibit the coexistence of (10) and (01) out-of-plane orientation domains, and increasing the growth temperatures and HCl flow-rates can enhance the growth of (10)-oriented β-Ga₂O₃. Off-angled (0001) sapphire substrates with off-angles (Δa) toward 〈110〉 have been introduced to control the in-plane domains. It was indicated that the (01)-oriented domains have been gradually eliminated with increasing the off-angles, and pure (10)-oriented β-Ga₂O₃ films with the best crystal quality reported so far have been obtained while the off-angle was ∼7°. The decrease of the domain boundaries and defects caused by the in-plane rotational domains have led to the improvement of the crystal quality of the as-grown films.