Polarity inversions within AlN films on sapphire exploiting silicon and oxygen diffusion during high temperature annealing

Overview & Synopsis

The polarity of III-nitride materials plays a crucial role in determining their physical properties and behavior. In this study, we investigate the formation and characteristics of elongated polarity inversion domains (IDs) in epitaxial aluminum nitride (AlN) layers grown on sapphire substrates during high temperature annealing. By employing various characterization techniques, we explore the chemical composition and atomic structure of the AlN epilayers. The domains exhibit distinct boundaries, indicating polarity inversions from aluminum Al-polar to N-polar and back to Al-polar. Significantly, we find that this inversion of polarity occurs post-growth during the annealing process, representing a novel finding of this study. The inclusion of silicon (Si) and oxygen (O) impurities during annealing proves crucial for the formation and stabilization of these domains. Chemical composition analysis demonstrates enrichments of Si and O at the boundaries of the domains, accompanied by reductions in Al and N concentrations. Using high-resolution transmission electron microscopy, we gain insights into the atomic structure of the IDs. The boundaries of the domains show an abrupt transition of polarity from Al-polar to N-polar, while convex boundaries exhibit a polarity reversal back to Al-polar. Our findings highlight the role of impurities and vacancies in the formation of IDs. Overall, this study provides significant insights into the post-growth inversion of polarity occurring during annealing in epitaxial AlN layers. The identification of IDs and the analysis of their characteristics contribute to a deeper understanding of polarity control and engineering in III-nitride materials, offering valuable implications for the design of electronic and optoelectronic devices based on polarity manipulation.