Defect Suppression in AlN Epilayer Using Hierarchical Growth Units

Growing AlN layers remains a significant challenge because it is subject to a large volume fraction of grain boundaries. In this study, the nature and formation of the AlN growth mechanism is examined by ab initio simulations and experimental demonstration. The calculated formation enthalpies of the constituent elements, including the Al/N atom, Al–N molecule, and Al–N₃ cluster, vary with growth conditions in N-rich and Al-rich environments. Using the calculation results as bases, we develop a three-step metalorganic vapor-phase epitaxy, which involves the periodic growth sequence of (i) trimethylaluminum (TMAl), (ii) ammonia (NH₃), and (iii) TMAl+NH₃ supply, bringing in hierarchical growth units to improve AlN layer compactness. A series of AlN samples were grown, and their morphological and luminescent evolutions were evaluated by atomic force microscopy and cathodoluminescence, respectively. The proposed technique is advantageous because the boundaries and defect-related luminescence derived are highly depressed, serving as a productive platform from which to further optimize the properties of AlGaN semiconductors