It was recalled that the threading dislocation density in GaN films grown directly onto flat sapphire substrates was typically >1010/cm2, which could significantly degrade the properties of GaN-based LEDs. An approach was presented here for reducing the threading dislocation density in a GaN layer using a variety of patterned sapphire substrates. A cone-shaped PSS produced by metal organic chemical vapour deposition was used for GaN deposition. Three types of GaN specimens were prepared at the initial nucleation stage, middle growth stage and final growth stage. The threading dislocations generated on the cone-shaped patterned sapphire substrates were analyzed by transmission electron microscopy and a strain mapping simulation using HRTEM images, which evaluated the residual strain distribution. A large number of threading dislocations was generated and the residual strain by the lattice distortions remained above the top of the cone-shaped regions. However, no threading dislocations or residual strain were observed at the slope of the cone-shaped regions. This may have been due to the formation of a GaN layer by lateral overgrowth at the slope of the cone-shaped regions, resulting in less lattice mismatch and incoherency between the GaN and sapphire. Overall, the threading dislocation density in the GaN layer could be reduced approximately 107/cm2 using cone-shaped patterned sapphire substrates.

Reducing Dislocation Density in GaN Films using a Cone-Shaped Patterned Sapphire Substrate. H.Y.Shin, S.K.Kwon, Y.I.Chang, M.J.Cho, K.H.Park: Journal of Crystal Growth, 2009, 311[17], 4167-70