Photomodulated reflectance spectroscopy (PR) and X-ray diffraction (XRD) were used for the characterization of highly strained ultrathin InAs quantum wells and modulated InGaAs layers in GaAs grown by metal-organic vapor phase epitaxy (MOVPE). Structures were grown in AIXTRON 200 reactor at 500 degrees C on (100) oriented GaAs substrates by sequential growth of InAs and GaAs layers. Various PR spectral features corresponding to optical transitions between ground and excited states in the layers were identified by means of simulation of electronic states in these structures using nextnano(3) quantum simulator. Different models of InAs layer growth were used to explain both the XRD and PR data. Results show that the Gaussian distribution of In atoms within few monolayers gives the best fit for our MOVPE grown ultrathin InAs layers. (c) 2006 Elsevier B.V. All rights reserved.