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The results of the study of the influence of Fe segregation into the unintentionally doped GaN channel layer in AlGaN/AlN/GaN heterostructures with Fe-doped GaN buffer layer on the electrical properties of two-dimensional electron gas are presented. A set of several samples was grown by metal-organic vapor-phase epitaxy and characterized by the van der Pauw method. The dependence of concentration and mobility of the two-dimensional electron gas on the channel layer thickness was analyzed theoretically by self-consistent solving of 1D Poisson and Schrödinger equations and scattering rate calculations within the momentum relaxation time approximation. It was found that both concentration and mobility decreases were responsible for the increase in the sheet resistance in the structures with a thinner channel layer, with a drop in mobility being not only due to ionized impurity scattering, but also due to a combined effect of weakening of screening, lower carrier energy and change in form-factors on scattering by interface roughness, dislocations and polar optical phonons. [ABSTRACT FROM AUTHOR]

A combined experimental and modeling study of stress and curvature evolution during (0001) GaN growth on (0001) 4H-SiC wafers is presented. It is shown that the GaN layers are under the compressive stress, whose magnitude depends on the composition of the AlGaN buffer that is used to accommodate the epitaxial strain between GaN and SiC. Processing of in situ curvature measurements suggests fast relaxation of the mismatch stress in GaN when the Al content is increased. At that, nucleation of new dislocations is possible, but the dislocation density decreases rapidly over a narrow part of the GaN layer due to large inclination and annihilation of the threading dislocations. Eventually, correlations between the curvature/stress/dislocation evolution and AlGaN buffer composition can be established and optimal strategy for the growth of crack-free structures can be suggested. [ABSTRACT FROM AUTHOR]