TEM analysis of threading dislocations in crack‐free Al x Ga 1− x N grown on an AlN(0001) template

Cross sectional transmission electron microscope (TEM) observation was performed to understand the behavior of threading dislocations (TDs) in an AlxGa1−xN layer epitaxially grown on an AlN/α-sapphire (0001) template. In the AlN template, TDs with c-component, or c-type and/or (a + c)-type, are annihilated so that most of the TDs remaining in the upper region of the AlN template are of a-type. In an AlxGa1−xN (x = 0) layer grown on the AlN template, pairs of the TDs are annihilated very quickly at or just above the hetero-interface of GaN/AlN. In the case of AlxGa1−xN (x = 0.27, 0.61), TDs penetrate into the AlxGa1−xN layer and some of these are arranged to be tied-up in the region several hundreds nm from the hetero-interface. The height of the region where TDs are arranged and the number of surviving TDs increase with the Al content x. These phenomena show that the TDs are annihilated by stress due to lattice mismatch between AlxGa1−xN and AlN.