Influence of GaN substrate miscut on the XRD quantification of plastic relaxation in InGaN

Strain relaxation of thick InGaN layers was studied in order to develop\ntechnology of InGaN templates for deposition of InGaN Quantum Wells (QWs) and\nInGaN layers of high-In-content. In this paper, we show that InGaN layers grown\non misoriented (0001)-GaN substrates relax by preferential activation of\ncertain glide planes for misfit dislocation formation. Substrate misorientation\nchanges resolved shear stresses, affecting the distribution of misfit\ndislocations within each dislocation set. We demonstrate that this mechanism\nleads to an anisotropic strain as well as a tilt of the InGaN layer with\nrespect to the GaN substrate. It appears that these phenomena are more\npronounced in structures grown on substrates misoriented toward <11-20>\ndirection than corresponding structures with <-1100> misorientation. These\nfeatures would influence the properties of the overgrown InGaN QWs and should\nbe taken into consideration during designing structures grown on relaxed InGaN\ntemplates. We reveal that the lattice of partially relaxed InGaN has a\ntriclinic deformation, thus requiring advanced XRD analysis. The presentation\nof just a single asymmetric reciprocal space map commonly practiced in the\nliterature can lead to misleading information regarding the relaxation state of\npartially relaxed wurtzite structures.\n