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Analysis of measured X-ray diffraction (XRD) data from heterostructures withfitting analysis is discussed, for which computer program was written. Latticeconstant and Poisson's ratio of a multi-compound layer is calculated fromVegard's law. Layers are strained in in-plane direction causing additionalstrain in out-of-plane direction and may be only partially strained. Forcrystals, wavelength-dependent electric susceptibility is represented asFourier series, components of which are calculated from atomic scatteringfactors, H\"onl anomalous dispersion correction terms and Debye-Waller factor.XRD intensity from heterostructures as a function of angle is calculated withdynamical diffraction theory using Takagi-Taupin differential equation solutionin form of recursive equations. XRD measurements are analyzed by fitting asimulated XRD curve to the measured XRD curve. Inverse problem related to curvefitting is solved with differential evolution where principal componentanalysis is used to reduce interparameter dependencies. For measurementanalysis a software was written with Java/Matlab, user interface (UI) of whichwas designed by taking into account feedback from users. With UI, it is reallyeasy to build a layer model, parameters of which are obtained by fitting asimulation to measurement. Software is also able to use GNU Octave andtherefore works without requiring any commercial components. Operability ofsimulation code of XRD curves was tested by comparing the curves simulated byit with curves simulated by 2 other software using single/multilayer InGaAs,GaAs and GaAsN structures. Software was tested by analyzing a measurementseries having been published previously. Software was observed to produceresults similar to other software and the fitting algorithm was observed towork efficiently.

XRD fitting analysis of semiconductor heterostructures [Puolijohderakenteiden r\"ontgendiffraktion sovitusanalyysi] (in Finnish)