AlN heteroepitaxy on sapphire by metalorganic vapour phase epitaxy using low temperature nucleation layers

Epitaxial films of AlN were grown on a sapphire substrate with a miscut of 0.38 degrees +/- 0.02 degrees towards the m-plane by metalorganic vapour phase epitaxy. A low temperature nucleation layer was used to overcome growth instabilities and to suppress the formation of inversion domains. This was followed by high temperature growth at 1250 degrees C. This two-step process, gives an acceptable material quality, (0002 FWHM=398 +/- 10 '' and 10-11 FWHM=940 +/- 23 ''), but resulted in a top surface dominated by large steps, with average heights of 6.0 +/- 0.5 nm. Atomic force microscopy analysis of step termination sites shows a staircase of single and double atomic steps, showing large steps are formed by the bunching of single steps, perhaps pinned by threading dislocations. To achieve a smooth top surface, 100 nm of the high temperature AlN is followed by growth at 1110 degrees C. This three step process largely eliminates the large steps resulting in a layer that has a smooth surface morphology and lower defect density (0002 FWHM=351 +/- 9 '' and 10-11 FWHM=761 +/- 19 ''). (C) 2013 Published by Elsevier B.V.