The initial stage of AlN film growth on 6H-SiC(0001) substrates by plasma-assisted, gas source molecular beam epitaxy (PAGSMBE) has been investigated in terms of growth mode and interface defects. Cross-sectional high resolution transmission electron microscopy (HRTEM) was used to observe the microstructure of the deposited films and the AlN/SiC interfaces. Surface morphologies and interface atomic structures were compared between films grown on vicinal and on-axis surfaces. Essentially atomically flat AlN surfaces were obtained using on-axis substrates. This is indicative of two-dimensional growth to a thickness of ∼15 Å. Islandlike features were observed on the vicinal surface. The coalescence of these features at steps gave rise to double positioning boundaries (DPBs) as a result of the misalignment of the Si/C bilayer steps with the Al/N bilayers in the growing film. The quality of thicker AlN films is strongly influenced by the concentration of DPBs formed at the outset of growth.
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