Hot phosphoric-acid etching and atomic force microscopy were used to etch and characterize various GaN materials, including free-standing GaN grown by hydride vapor-phase epitaxy, metal-organic chemical-vapor deposition GaN films on sapphire and silicon carbide, and homo-epitaxial GaN films on polished freestanding-GaN wafers. It was found that etching at optimal conditions could accurately reveal the dislocations in GaN; however, the optimal etch conditions were different for samples grown by different techniques. The as-grown hydride vapor-phase epitaxy samples were most easily etched, while the metal-organic chemical-vapor deposition homo-epitaxial films were most difficult to etch. Etch-pit density ranging from 4 x 106 to 5 x 109/cm2 was measured in close agreement with the respective dislocation density determined from transmission electron microscopy.

Acid Etching for Accurate Determination of Dislocation Density in GaN. X.Xu, R.P.Vaudo, J.Flynn, G.R.Brandes: Journal of Electronic Materials, 2002, 31[5], 402-5