The structure and optical properties of the heterostructures, which contain an ultra-thin InGaN layers with GaN
or AlGaN barriers, grown by MOCVD method were investigated by photoluminescence and high resolution X-ray
diffraction (HRXRD) tehnigue. The exciton localization energy, Urbah energy and charge carries activation energies
were obtained from analysis of the temperature dependences of the photoluminescence spectra for the In-rich areas
(QDs). In these structures the In-rich areas are shown to appear in ultrathin InGaN layers due to phase decomposition.
That leads to exciton and carrier localization in fluctuation minima, which prevents them from tranport to nonradiative
recombination centres. The indium composition in the InGaN QDs were obtained using theoretical model, which
describes the electron transition energy as a function of In-rich areas parameters. The parameters such as deformation of
InGaN/GaN region and layer thickness were determined from HRXRD. The suggested approach is supposed to be
effective method for analysis of the optical properties of InGaN/GaN heterostructures.