Dielectric properties of Si_3-ξGe_ξN₄ and Si_3-ξC_ξN₄: A density functional study

Using first principles calculations, we have studied the dielectric properties of crystalline α- and β-phase silicon germanium nitrides and silicon carbon nitrides, A 3 - ξ B ξ N4 (A = Si, B = Ge or C, ξ = 0, 1, 2, 3). In silicon germanium nitrides, both the high-frequency and static dielectric constants increase monotonically with increasing germanium concentration, providing a straightforward way to tune the dielectric constant of these materials. In the case of silicon carbon nitrides, the high-frequency dielectric constant increases monotonically with increasing carbon concentration, but a more complex trend is observed for the static dielectric constant, which can be understood in terms of competition between changes in the unit-cell volume and the average oscillator strength. The computed static dielectric constants of C3N4, Si3N4, and Ge3N4 are 7.13, 7.69, and 9.74, respectively. © 2013 AIP Publishing LLC.