InGaN layers capped with GaN were annealed at 550 ℃ for 1 hour.During annealing,cracks appeared and dissolved InGaN penetrated through the microcracks into the V-pits to form indium-rich nanoprecipitates.Some precipitates,in-situ annealed under nitrogen ion irradiation by MBE,were confirmed to be cubic GaN on the tops of precipitates,formed by nitriding the pre-existing Ga droplets under nitrogen ions irradiation.