Dislocations around precipitates in undoped AlGaN were investigated by transmission electron microscopy. The dislocation images were obtained under various diffraction conditions. The dislocations were classified into 2 types: a pure edge dislocation loop and a closely-coiled helical dislocation. Both types of dislocation were found to depend upon the shape and size of the precipitate sources. It was suggested that the pure edge dislocation loop resulted from homogeneous shear stresses and the closely-coiled helical dislocation was caused by spherically symmetrical stress concentrations around the ends of precipitates and by chemical forces due to defect concentration changes.

Dislocations around Precipitates in AlGaN Epilayers. J.Kang, S.Tsunekawa, A.Kasuya: Journal of Materials Research, 2002, 17[8], 2007-11