Composition-Dependent Structural and Electronic Properties of α-(Si1−x C x )3N4

The highly unusual structural and electronic properties of the α-phase of (Si1−x C x )3N4 are determined by density functional theory (DFT) calculations using the Generalized Gradient Approximation (GGA). The electronic properties of α-(Si1−x C x )3N4 are found to be very close to those of α-C3N4. The bandgap of α-(Si1−x C x )3N4 significantly decreases as C atoms are substituted by Si atoms (in most cases, smaller than that of either α-Si3N4 or α-C3N4) and attains a minimum when the ratio of C to Si is close to 2. On the other hand, the bulk modulus of α-(Si1−x C x )3N4 is found to be closer to that of α-Si3N4 than of α-C3N4. Plasma-assisted synthesis experiments of CN x and SiCN films are performed to verify the accuracy of the DFT calculations. TEM measurements confirm the calculated lattice constants, and FT-IR/XPS analysis confirms the formation and lengths of C−N and Si−N bonds. The results of DFT calculations are also in a remarkable agreement with the experiments of other authors.