Transformation of N-Polar Inversion Domains from AlN Buffer Layers during the Growth of AlGaN Layers

The structural properties and crystal quality of AlxGa1 - xN/AlN/Al2O3 heterostructures grown by ammonia-assisted molecular-beam epitaxy with a high silicon concentration in the AlxGa1 - xN:Si layers are studied by atomic force microscopy and dynamic secondary-ion mass spectrometry. It is shown that if AlN buffer layers of metal polarity contain inversion domains of nitrogen polarity, during subsequent growth of the AlxGa1 - xN:Si layers, inversion domains do not grow to the surface, but change their nitrogen polarity for metal polarity. At the place of AlN inversion domains, broadening AlxGa1 - xN columns of metal polarity grow, which coalesce in a homogeneous film with the Me-polar matrix surrounding them. The thickness corresponding to complete intergrowth increases with the Al content in the layers.