Suppression of threading dislocations in epitaxial AlN layer on sapphire by helium ion implantation-induced nanocavities

Heteroepitaxy enables the monolithic integration of diverse functional materials on a single substrate but suffers from high threading dislocation densities (TDDs) due to lattice mismatch. Here, we introduce a strategy to further reduce TDD in thin AlN epilayers grown on sapphire, surpassing the saturation limit of conventional thermal annealing. We show that He implantation followed by thermal annealing could significantly reduce TDD in the thin AlN epilayer by an order of magnitude with improved surface quality. By systematical characterization, we demonstrate that the reduction in TDD is driven by He-ion implantation-induced nanocavities at the epitaxial interface as it can act as a facilitator for dislocation annihilation. The underlying mechanism for this effect involves both nanocavity-induced local strain fields and the reorientation of mosaic blocks via epitaxial interface decoupling, which collectively drive the dislocations aggregation and the subsequent annihilation. In addition, the implantation-generated vacancies also contribute to the dislocation annihilation by enabling and enhancing migration-mediated dislocation motion. Since the strategy presented in this work is based on the standard semiconductor processing technology, it is a promising and potentially universal route for TDD reduction and warrants further investigation in other semiconductor heterostructure epitaxy systems, such as a Si-based platform. The findings may provide a simple route for the monolithic integration of diverse functional materials on a single substrate toward more-than-Moore semiconductor technologies.