Structural Inhomogeneities and Impurity Incorporation in Growth of High-Quality Ammonothermal GaN Substrates

Abstract

Ammonothermal Gallium Nitride (GaN) substrates are the most promising substrates for homoepitaxial growth of GaN films having low dislocation density. Growth-induced structural inhomogeneities in these substrates were investigated by high-resolution X-ray topography (HR-XRT) and high-resolution X-ray diffraction (HR-XRD). A one-to-one correlation of defects was observed in photoluminescence imaging. From the HR-XRD intrinsic rocking curve widths were found to be 16 arcsecs indicating superior crystalline quality. The lattice constants were measured from symmetric and asymmetric reflections to be similar to bulk values indicting low sample strian. The true dislocation density, from the HR-XRT images, was observed to be of the order of 102 cm–2 in the samples, and the radius of curvature was greater than 600 m. Growth striations were observed in the a and m-pane samples and are attributed to inhomogeneity in impurity incorporation during growth. Photoluminescence imaging showed deep level luminescent centers along the growth striations.