Structural, Electronic, and Thermodynamic Properties of Tetragonal t-Si(x)Ge(3−x)N(4)

The structural, mechanical, anisotropic, electronic, and thermal properties of t-Si(3)N(4), t-Si(2)GeN(4), t-SiGe(2)N(4), and t-Ge(3)N(4) in the tetragonal phase are systematically investigated in the present work. The mechanical stability is proved by the elastic constants of t-Si(3)N(4), t-Si(2)GeN(4), t-SiGe(2)N(4), and t-Ge(3)N(4). Moreover, they all demonstrate brittleness, because B/G < 1.75, and v < 0.26. The elastic anisotropy of t-Si(3)N(4), t-Si(2)GeN(4), t-SiGe(2)N(4), and t-Ge(3)N(4) is characterized by Poisson’s ratio, Young’s modulus, the percentage of elastic anisotropy for bulk modulus A(B), the percentage of elastic anisotropy for shear modulus A(G), and the universal anisotropic index A(U). The electronic structures of t-Si(3)N(4), t-Si(2)GeN(4), t-SiGe(2)N(4), and t-Ge(3)N(4) are all wide band gap semiconductor materials, with band gaps of 4.26 eV, 3.94 eV, 3.83 eV, and 3.25 eV, respectively, when using the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional. Moreover, t-Ge(3)N(4) is a quasi-direct gap semiconductor material. The thermodynamic properties of t-Si(3)N(4), t-Si(2)GeN(4), t-SiGe(2)N(4), and t-Ge(3)N(4) are investigated utilizing the quasi-harmonic Debye model. The effects of temperature and pressure on the thermal expansion coefficient, heat capacity, Debye temperature, and Grüneisen parameters are discussed in detail.