Evolution of phase separation in Inx Ga1-x N alloys (x∼0.65) grown on AlN/sapphire templates by metal organic chemical vapor deposition has been probed. It was found that growth rate, GR, is a key parameter and must be high enough (>0.5 μm/h) in order to grow homogeneous and single phase InGaN alloys. Our results implied that conditions far from thermodynamic equilibrium are needed to suppress phase separation. Both structural and electrical properties were found to improve significantly with increasing GR. The improvement in material quality is attributed to the suppression of phase separation with higher GR. The maximum thickness of the single phase epilayer tmax (i.e., maximum thickness that can be grown without phase separation) was determined via in situ interference pattern monitoring and found to be a function of GR. As GR increases, tmax also increases. The maximum value of tmax for In0.65 Ga0.35 N alloy was found to be ∼1.1 μm at GR >1.8 μm/h.