Effects of composition on the properties of mixed CdSi_1-xGe_xAs₂ chalcopyrites as explored by the first-principles calculations

The structural, electronic, optical and elastic properties of the CdGeAs₂ and CdSiAs₂ chalcopyrites and their CdSi_1-xGe_xAs₂ mixtures were calculated using the first-principles methods. Good agreement with the available experimental data was achieved for both neat compounds. Based on this, the mixed CdSi_1-xGe_xAs₂ compounds were explored in details. Two different models - the virtual crystal approximation (VCA) and the supercell (SC) model - were used to analyze the impact of the second cation substitution on the above-mentioned properties of the mixed materials in the whole range of the Ge/Si concentration from x=0 to x=1. It has been shown that the lattice constants, band gaps, refractive indexes, elastic constants and Debye temperature all exhibit linear variation with the second cation composition. The linear dependences of all these parameters allow for their numerical estimation for any composition in the studied range.