An AlN/GaN superlattice structure for the use as low index material in distributed Bragg reflectors in the blue-violet spectral region was studied by transmission electron microscopy in cross section and plan view. The superlattice was found to partially relax during growth via the introduction of threading dislocations. Dislocation loops were found to form spontaneously at discrete superlattice thicknesses indicating the accumulation of point defects. Such defects might hamper the light transmission in the targeted wavelength range.

Relaxation in Crack-Free AlN/GaN Superlattices. R.Kröger, C.Kruse, C.Roder, D.Hommel, A.Rosenauer: Physica Status Solidi B, 2006, 243[7], 1533-6