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°±0.02° 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 °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 °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′′).