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 lattic e matched to its binary analog GaAs. The calculated band structures show th at 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 be tween 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 s tannite structure. However, the band gap and the mixing energy of the alloy at higher temperature depend sensitively on the local short-range order. T he calculated formation energies of the (ZnGeAs2)(n)(GaAs)(2n) superlattice s along the [001] direction show strong nonmonotonic behavior, with the for mation energy DeltaH(n) maximized at n = 2. We compared our results for the ZnGeAs2/GaAs system to the well-studied CuGaSe2/ZnSe system. The differenc es between these two systems are explained in terms of their ionicity and t heir relative strength of the anion p and cation d couplings.