Effect of vicinal off-cut substrates on the basal stacking fault density in nonpolar a-GaN epilayers

► Nonpolar a-GaN epilayers were grown on off-cut r-sapphire substrates using MOCVD. ► The effect of the off-cut angle on the formation of BSFs was microstructurally investigated using TEM. ► From HRTEM images, we found that formation mechanism of BSFs was attributed to the tilted growth of the a-GaN epilayers. ► Formation and reduction mechanisms of BSFs in a-GaN epilayers were discussed.