We report on material properties of GaN thin films grown on (0001) exactly
oriented sapphire substrates by MOCVD. The crystalline quality of the sampl
es was estimated by several techniques: Nomarski microscopy, transmission e
lectron microscopy (TEM) and high resolution X-ray diffraction (HRXRD). It
is shown that a quantitative evaluation of defects (dislocations) in GaN, c
an 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 B
ragg reflections, symmetrical and asymmetrical, wen investigated. The analy
sis clearly illustrates that gradations in the crystalline qualities of GaN
epilayers can be well evidenced and quantified by this method. The reasona
ble self-consistency of the results allows to approach an estimation of dis
location content and arrangement. (C) 1999 Elsevier Science S.A. All rights
reserved.