((3)over-bar10)-Oriented -Ga₂O₃ grown on (0001) sapphire by halide vapor phase epitaxy: growth and structural characterizations

In general, beta-Ga2O3 films with ((2) over bar 01) out-of-orientation have been widely obtained and reported on (0001) sapphire substrates by various growth methods. In this paper, the unusual ((3) over bar 10)-oriented beta-Ga(2)O3 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 ((3) over bar 10) beta-Ga2O//(0001) alpha-Al2O3 has been confirmed by XRD and HRTEM analysis. Under most growth conditions, beta-Ga2O films exhibit the coexistence of ((3) over bar 10) and ((2) over bar 01) out-of-plane orientation domains, and increasing the growth temperatures and HCl flow-rates can enhance the growth of ((3) over bar 10)-oriented beta-Ga2O. Off-angled (0001) sapphire substrates with off-angles (Delta a) toward <11<(2)over bar>0> have been introduced to control the in-plane domains. It was indicated that the ((2) over bar 01)-oriented domains have been gradually eliminated with increasing the off-angles, and pure ((3) over bar 10)-oriented beta-Ga2O films with the best crystal quality reported so far have been obtained while the off-angle was similar to 7 degrees. 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.