Modelling of the defect structure in GaN MOCVD thin films by X-ray diffraction

We report on material properties of GaN thin films grown on (0001) exactly oriented sapphire substrates by MOCVD. The crystalline quality of the samples was estimated by several techniques: Nomarski microscopy, transmission electron microscopy (TEM) and high resolution X-ray diffraction (HRXRD). It is shown that a quantitative evaluation of defects (dislocations) in GaN, can be obtained using a model developped by Hordon and Averbach (M.J. Hordon, B.L. Averbach, act. Met. 9 (1961) 237-246) and based on X-ray peaks Full Width at Half Maximum (FWHM) measurements. For each sample, more than ten Bragg reflections, symmetrical and asymmetrical, wen investigated. The analysis clearly illustrates that gradations in the crystalline qualities of GaN epilayers can be well evidenced and quantified by this method. The reasonable self-consistency of the results allows to approach an estimation of dislocation content and arrangement. (C) 1999 Elsevier Science S.A. All rights reserved.