High resolution X-ray diffraction study of the Si doping influence on columnar crystal growth of GaN layers

The morphology of hexagonally shaped coherent domains in undoped and Si-doped GaN has been characterised by X-ray determination of lateral and vertical correlation lengths and the twist (alpha(phi)) and tilt (alpha(Omega)) angles. In the present paper all measured symmetrical omega scans have Gaussian shape. The extrapolation method based on theoretically derived expression for omega scan diffraction profile measured in the triple axis mode is presented. The method was applied for determination of values of L lateral correlation length and alpha(Omega). In order to examine the shape and spatial misorientations of coherent domains the measurements were performed for scattering vectors q(x) parallel to all [hk0] azimuthal directions. From a detailed analysis of plot L against q(x) we came to the conclusion that both in undoped and Si-doped samples the coherent domains in GaN layer are of quasi hexagonal shape. This is the first evidence of hexagonal shape of coherent domains concluded from X-ray data. However, the coherent domains of Si-doped layer exhibit a higher regularity of geometrical shape. The extrapolation method developed in the present work for determination of in-plane size of coherent domains and their tilt angle is applicable to a strong texture (about growth direction) of columnar coherent domains. (C) 2003 Elsevier B. V. All rights reserved.