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

Abstract 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 ( α Φ ) and tilt ( α Ω ) angles. In the present paper all measured symmetrical ω scans have Gaussian shape. The extrapolation method based on theoretically derived expression for ω 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 α Ω . In order to examine the shape and spatial misorientations of coherent domains the measurements were performed for scattering vectors q x parallel to all [ hk 0] 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.