Reduction of dislocation density in epitaxial GaN layers by overgrowth of defect-related etch pits

GaN templates grown by the metal organic chemical vapor deposition method were etched in a defect-selective molten salts eutectic and were subsequently overgrown by a GaN layer using the hydride vapor phase epitaxy (HVPE) method. Optimized conditions of etching and of HVPE growth processes resulted in a significant reduction of the dislocations density (DD). Local areas virtually free of dislocations were obtained on ∼50% of the surface, while the average DD was reduced from 3×10⁹ cm^-2 in the template to about 2×10⁷ cm^-2 in the HVPE-grown GaN layer. A model has been developed to explain the mechanism of reduction of the DD during the overgrowth process. The model was confirmed by the photoetching of cleaved layers.