On the origin of a-type threading dislocations in GaN layers

Abstract

The origin of threading dislocations (TDs) in GaN epitaxial layers grown on sapphire (0001) substrate is investigated using moiré fringes from plan-view transmission electron microscopy. The studied samples are nucleation layers deposited at 560°C for times ranging from 20sto180s. This initial stage growth gives rise to islands which are randomly rotated and relaxed with misfit dislocations. The islands that start to coalesce from 60s growth time keep this random orientation and this leads to the bending of 60° misfit dislocations in the interface plane to form a-type TDs inside low angle boundaries.