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In situ asymmetric island sidewall growth(AISG)was developed to improve the crystalline quality of the(11-22)GaN films on m-sapphire.By AISG the Ga-face facet growth along the +c [0001] inclined direction was enhanced at the early island growth stage.The +c region of the island overlapped the-c region of neighboring island during island coarsening and coalescence along [-1-123].As a result,high-density stacking faults(SFs)usually formed in the-c regions were blocked by the +c regions on top,which is schematically drawn in Fig.1.X-ray diffraction and Raman studies show high-quality semipolar(11-22)GaN films were achieved by AISG(see Fig.2).Low temperature cathodoluminescence spectra show a significant increase of near band-edge emission(NBE)and decrease of SFs emission due to the improvement of crystalline quality in the semipolar GaN prepared by AISG.