Interpretation of double x-ray diffraction peaks from InGaN layers

The presence of two, or more, x-ray diffraction (XRD) peaks from an InGaN epilayer is sometimes regarded as an indicator of phase segregation. Nevertheless, detailed characterization of an InGaN/GaN bilayer by a combination of XRD and Rutherford backscattering spectrometry (RBS) shows that splitting of the XRD peak may be completely unrelated to phase decomposition. Wurtzite InGaN/GaN layers were grown in a commercial reactor. An XRD reciprocal space map performed on the (105) plane shows that one component of the partially resolved InGaN double peak is practically aligned with that of the GaN buffer, indicating that part of the layer is pseudomorphic to the GaN template. The other XRD component is shown to have the same indium content as the pseudomorphic component, from a consideration of the effect of strain on the c- and a-lattice constants. The composition deduced from XRD measurements is confirmed by RBS. Depth-resolving RBS channeling angular scans also show that the region closer to the GaN/InGaN interface is nearly pseudomorphic to the GaN substrate, whereas the surface region is almost fully relaxed.