Study of individual grown-in and indentation-induced dislocations in GaN by defect-selective etching and transmission electron microscopy

Vickers diamond indentation at 370 degreesC has been employed to introduce dislocations into the plate-like (000-1) N-polar GaN single crystals. It has been established that using standard Vickers diamond indenter, well-defined 'rosettes' of defects are formed under 1.5-2 N load applied for 10 min. The resolved patterns of dislocation-related etch pits are formed using molten KOH-NaOH eutectic (E) at 200 degreesC for 1.5-2 min. Individual grown-in dislocations are revealed by this E etch in the GaN matrix. Transmission Electron Microscopy confirmed the correlation of etch pits to individual dislocations emerging at the surface. Nano-crystalline material was found in the highly deformed central region of the indentation rosette. The structure of these nano-crystals was analyzed using electron diffraction. Speculative explanation on a phase transition induced by high local pressure is briefly discussed. (C) 2001 Elsevier Science B.V. All rights reserved.