The threading dislocation density in GaN films grown directly on flat sapphire

substrates was typically >1010/cm2, which can deteriorate the properties of GaNbased

LEDs significantly. This paper reports an approach to 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 were generated and the residual strain by the

lattice distortions remained above the top of the cone-shaped regions. However, no

threading dislocations and residual strain were observed at the slope of the coneshaped

regions. This might be 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. In conclusion, the

threading dislocation density in the GaN layer could be reduced significantly,

approximately 107/cm2, using the 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