High resolution X-ray diffraction defect structure characterization in Si-doped and undoped GaN films

The effect of Si doping (NSi∼3×1018 cm−3) on crystalline quality of GaN epitaxial layers grown on sapphire c face was studied by high resolution X-ray diffraction including several Bragg reflections in different scan directions, reciprocal space maps, radial scans, and measurements of radii of curvature. Elastic and hydrostatic strain components were derived taking into account strains introduced in the sapphire substrate by the highly mismatched GaN layer. Si-doped and undoped GaN layers were grown by atmospheric pressure MOCVD technique using the same growth conditions. All the layers were under compression but with slightly higher stress in the undoped layer, while the hydrostatic strain component remained unchanged. It was found that doping of GaN by Si decreased edge dislocation density and increased screw dislocation density. It could be concluded that edge-type threading dislocation arrangement, piled up in small-angle columnar grain boundaries, dominated in both samples.