The effect of image forces in GaN pyramidal nanorod structures was investigated to develop dislocation-free light-emitting diodes. A model based on the eigenstrain method and nonlocal stress was developed to demonstrate that the pyramidal nanorod efficiently ejects dislocations out of the structure. Two possible regimes of filtering behavior were found: cap-dominated and base-dominated. The cap-dominated regime was shown to be the more effective filtering mechanism. Optimal ranges of fabrication parameters that favour a dislocation-free light-emitting diodes were predicted and corroborated by resorting to available experimental evidence. The filtering probability was summarized as a function of practical processing parameters: the nanorod radius and height. The results suggested an optimal nanorod geometry with a radius of some 50b (26nm) and a height of some 125b (65nm), in which b was the magnitude of the Burgers vector for the GaN system studied. A filtering probability of greater than 95% was predicted for the optimal geometry.

GaN Nanostructure Design for Optimal Dislocation Filtering. Z.Liang, R.Colby, I.H.Wildeson, D.A.Ewoldt, T.D.Sands, E.A.Stach, R.E.García: Journal of Applied Physics, 2010, 108[7], 074313