Growth of GaN films with low oxygen concentration using Ga2O vapor and NH3

► Surface morphology changed from rough to smooth with the NH3 concentration increased. ► Oxygen concentration in growth layer decreased with increasing NH3 concentration. ► GaN layer with growth rate of 12 μm/h and [O] of 2.5×1017 atoms/cm3 was obtained. ► Relationship between surface morphology and [O] was clarified.