X-ray measurement of a microdistortion tensor and its application in an analysis of the dislocation structure of thick GaN layers obtained by hydrochloride gaseous-phase epitaxy

The method of two- and three-crystal x-ray diffractometry (TCD) is used for studying the dislocation structure of thick GaN layers grown by chloride g aseous-phase epitaxy (CGE) on sapphire, as well as on a thin GaN layer, whi ch is grown by the metalloorganic synthesis (MOS) method. Five components o f the microdistortion tensor < epsilon (ij)> and the sizes of the coherent scattering regions along the sample surface and along the normal to it are obtained from the measurements of diffracted intensity in the Bragg and Lau e geometries. These quantities are used to analyze the type and geometry of the dislocation arrangement and to calculate the density of the main types of dislocations. The density of the vertical screw dislocations, as well a s of the edge dislocations, decreases (by a factor of 1.5 to 3) during grow th on a thin GaN layer. The diffraction parameters of the thick layer on th e MOS-GaN substrate suggest that it has a monocrystalline structure with in clusions of microcrystalline regions. (C) 2000 MAIK "Nauka/ Interperiodica" .