TEM study of the behavior of dislocations during ELO of GaN

We study by transmission electron microscopy (TEM) the mechanisms of the de fect reduction in metalorganic vapor phase epitaxy (MOVPE) ELO of GaN on a sapphire substrate. A first growth step induces the bending of the dislocat ions and thus allows a drastic reduction of the density of vertically threa ding defects. In the second step, the dislocations keep their line in the b asal plane and propagate horizontally towards the coalescence boundary with the GaN material coming from the adjacent window. We describe their differ ent behaviors in the boundary. Finally, plan view observations reveal that large areas are free of dislocations at the TEM scale.