Influence of HCl concentration in source solution and growth temperature on formation of alpha-Ga2O3 film via mist-CVD process

We have examined the effect of synthesis conditions on a-Ga2O3 film, one of the ultra-wide bandgap semiconductors, on c-plane sapphire substrate via mist CVD process. The resultant film is dominantly composed of a-Ga2O3 phase, but a small amount of ?-Ga2O3 phase coexists when the growth temperature is higher. The source solution containing higher concentration of HCl expands the range of temperatures at which single-phase a-Ga2O3 is grown and suppresses the inclusion of ?-Ga2O3 at higher growth temperatures. Moreover, the growth with higher concentration of HCl up to 0.66 mol l(-1) increases the growth rate and improves the surface roughness. Thus, HCl has a crucial role in the selective growth of a-Ga2O3 and the quality of the film. Also, some pits are observed at the surface of a-Ga2O3 and ?-Ga2O3 is precipitated inside the pit defect when the concentration of HCl is low and the growth temperature is high.