First-principles calculations to investigate structure and fundamental physical properties of BaM2As2 (M = Mg, Zn, Cd) and their alloys

The energetic stability, elastic parameters, electronic structures, effective masses, and optical properties of BaM2As2 (M = Mg, Zn, Cd) and their alloys are revealed for the first time. The results show that it is preferred to adopt the trigonal phase for BaMg2As2 and BaCd2As2, while it may have an additional stable trigonal phase for BaZn2As2 except for the reported experimental phases. The dynamical stability is identified for four novel compounds. The important elastic properties are examined for these compounds and the mechanical stability is confirmed. The band gap energy is greatly narrowed from BaMg2As2 (1.64 eV) to BaCd2As2 (0.80 eV). It is found for BaZn2As2 that the electronic properties of three phases are different from each other. Besides, the band gap calculations can agree with the available experimental results. The bandgap transition behavior is disclosed for three alloys, and their optoelectronic properties are concerned. Both Ba(Mg0.5Zn0.5)2As2 and Ba(Mg0.5Cd0.5)2As2 show the desirable optoelectronic properties including the direct band gap, smaller effective masses, lower exciton binding energy, and high absorption coefficient. The findings are expected to be helpful for discovering novel stable inorganic compounds for potential photovoltaic applications.