Structural and microstructural characterization of GaN thin films and GaN-based heterostructures grown on sapphire substrates

The primary cause for x-ray rocking curve broadening in epitaxial GaN grown on basal plane sapphire is determined by studying the reciprocal space maps of both symmetric and asymmetric reflections. The propagation of threding dislocations in GaN/AlGaN-based heterostructures is studied through cross sectional transmission electron microscopy. A density of screw and mixed dislocations less than 107 cm ^-2 in these heterostructures is achieved.