The polarity of GaN films and AlN buffer layers, grown onto the (00•1)Si surface of 6H-SiC using electron cyclotron resonance plasma-enhanced molecular beam epitaxy, was investigated by means of convergent-beam electron diffraction and high-resolution electron microscopy. In the case of the AlN buffer layers, which contained a very high density of defects, the polarity was determined by using extensive high-resolution electron microscopy and image simulation. In both cases, the simulations were in good agreement with the experimental results, and demonstrated that the free surfaces of the GaN and AlN layers were Ga- and Al-terminated, respectively. Moreover, (¯12•0) prismatic planar defects which were observed in the AlN layers were identified as being stacking faults, and analysis of various areas of the specimens confirmed that the layers were unipolar.

P.Vermaut, P.Ruterana, G.Nouet: Philosophical Magazine A, 1997, 76[6], 1215-34