Atom probe of GaN/AlGaN heterostructures: The role of electric field, sample crystallography and laser excitation on quantification

• Published in: Ultramicroscopy 2019-11, Vol.206, p.112813-112813, Article 112813
• Main Authors: Morris, Richard J.H., Cuduvally, Ramya, Melkonyan, Davit, Zhao, Ming, van der Heide, Paul, Vandervorst, Wilfried
• Format: Article
• Language: English
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/j.ultramic.2019.112813

•Analysis conditions and sample structure influence on the quantification for GaN and AlGaN studied and explained.•Strong compositional variation for GaN and AlGaN shown to be field dependent.•Demonstration of how the localized lateral field variation over the tip apex due to the sample crystallography impacts on the lateral stoichiometry and reconstruction of GaN/AlGaN device heterostructures.•Conditions for the accurate stoichiometric quantification of GaN determined. Scaling and non-planar architectures are key factors helping to advance the semiconductor field. Accurate 3-dimensional atomic scale information is therefore sought but this presents a significant metrology challenge. Atom probe tomography has emerged as a strong candidate to fulfill this role, but before it can be considered an accurate and precise metrology method, numerous difficulties need to be overcome. In this paper we highlight some of these in respect to the analysis of GaN/AlGaN device heterostructures. Although a significant range of conditions for accurate GaN stoichiometric analysis were readily achieved, a more limited range of analysis conditions that yielded an accurate Al site fraction for AlGaN was observed because the Al was typically overestimated. Moreover, the low index planes of the material resulted in pole and zone lines given their lower evaporation fields and are clearly observed on the detector due to related ion trajectory aberrations representative of local field variations present. As a result of the strong compositional bias of GaN analysis with field, the Ga and N concentrations were found to vary by ∼20 at.% over the tip apex. For the AlGaN this variation was smaller (