Structural and electronic properties of ZnGeAs2 -: art. no. 195210

Using a first-principles band-structure method based on density functional theory, we have studied the structural and electronic properties of ZnGeAs2. In agreement with experimental data, ZnGeAs2 is found to be nearly lattice matched to its binary analog GaAs. The calculated band structures show that ZnGeAs2 in the chalcopyrite structure has a direct band gap, about 0.31 eV smaller than the band gap of GaAs. The calculated valence-band offset between ZnGeAs2 and GaAs is 0.18 eV; thus, the band alignment of the ZnGeAs2/GaAs system is type I, with both holes and electrons localized on ZnGeAs2. We also find that at low temperature, (ZnGeAs2)(0.5)(GaAs) forms a stable stannite structure. However, the band gap and the mixing energy of the alloy at higher temperature depend sensitively on the local short-range order. The calculated formation energies of the (ZnGeAs2)(n)(GaAs)(2n) superlattices along the [001] direction show strong nonmonotonic behavior, with the formation energy DeltaH(n) maximized at n = 2. We compared our results for the ZnGeAs2/GaAs system to the well-studied CuGaSe2/ZnSe system. The differences between these two systems are explained in terms of their ionicity and their relative strength of the anion p and cation d couplings.