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Spectrally selective TiAlN/TiAlON/Si₃N₄ tandem absorber was deposited on copper, glass, stainless steel, nickel and nimonic substrates using a reactive direct current magnetron sputtering system. In this tandem absorber, TiAlN acts as the main absorber layer, Si₃N₄ acts as an antireflection coating and TiAlON acts as a semi-absorber layer. The tandem absorber was characterized using solar spectrum reflectometer and emissometer, cross-sectional transmission electron microscopy (XTEM), selected area diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy (XPS) and phase-modulated ellipsometry techniques. The compositions and thicknesses of the individual component layers were optimized to achieve high solar absorptance and low thermal emittance. The XPS data indicated that, for the TiAlN and Si₃N₄ layers, nitrogen was attached to Ti, Al and Si, whereas …