Crystallinity Evaluation and Dislocation Observation for an Aluminum Nitride Single-Crystal Substrate on a Wafer Scale

The crystallinity of a 35-mm-diameter AlN single-crystal substrate grown by physical vapor transport was investigated using x-ray diffraction and Raman spectral mapping. Dislocations in the same sample were observed using an etch pit method, synchrotron x-ray topography, and transmission electron microscopy. The central area of a diameter of 25 mm was featured with high crystallinity and high uniformity, whereas the rim area showed degradation in crystallinity. An improvement in the radius of curvature was confirmed along the growth direction of [0001¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ 000\bar{1} $$\end{document}]. The dislocations were revealed as etch pits, and the position-dependent etch pit density was analyzed across the whole wafer. Transmission electron microscopy showed that under the current chemical etching condition, the size of the etch pits in the [112¯0]\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ 11\bar{2}0] $$\end{document} diagonal direction was approximately linearly proportional to the magnitude of the Burgers vectors, and therefore could be used to classify dislocations.