Non-polar a-GaN films grown on r-sapphire by hydride vapor phase epitaxy (HVPE) are studied using transmission electron microscopy (TEM). Despite the small lattice mismatch in a-GaN ([1 0 (1) over bar 0] similar to 1.1% and [0 00 1] similar to 16%), high dislocation and basal stacking fault densities are observed. Epitaxial lateral overgrowth (ELO) technique is implemented in order to reduce the defect density. ELO reduces both densities by two orders of magnitude: the dislocation density is reduced from 1 x 1010 to 3 x 108 cm(-2) and the stacking fault density is reduced from 1 x 10(6) to 4 x 10(4) cm(-1). Threading dislocations (TDs) are observed in the ELO mask openings with screw and mixed characters which have Burgers vectors (b) over right arrow = 1/3[1 1 (2) over bar 0] and (b) over right arrow = 1/3[1 1 (2) over bar 3] respectively. In the ELO areas, three kind of dislocations are observed: screw dislocations with (b) over right arrow = 1/3[1 1 (2) over bar 0], edge dislocations with (b) over right arrow = 1/3[(2) over bar 1 1 0] and partial dislocations (PDs) with (b) over right arrow = 1/3[1 0 (1) over bar 0] and (b) over right arrow = 1/6[2 0 (2) over bar 3]. Basal stacking faults (BSFs) of the type I-1 ((R) over right arrow = 1/6[2 0 (2) over bar 3]) and I-2 ((R) over right arrow 1/3[1 0 (1) over bar 0]), and prismatic stacking faults (PSFs) with a (R) over right arrow = [1 (1) over bar 0 1]Toil are also observed. Cathodoluminescence, spectra and imaging, has shown that TDs are non-radiative recombination centers contrary to BSFs. (C) 2011 Elsevier B.V. All rights reserved.