Composition-Dependent Structural and Electronic Properties of α-(Si_1−xC_x)₃N₄

Abstract

The highly unusual structural and electronic properties of the R-phase of (Si 1-x C x ) 3 N 4 are determined by density functional theory (DFT) calculations using the Generalized Gradient Approximation (GGA). The electronic properties of R-(Si 1-x C x ) 3 N 4 are found to be very close to those of R-C 3 N 4 . The bandgap of R-(Si 1-x C x ) 3 N 4 significantly decreases as C atoms are substituted by Si atoms (in most cases, smaller than that of either R-Si 3 N 4 or R-C 3 N 4 ) and attains a minimum when the ratio of C to Si is close to 2. On the other hand, the bulk modulus of R-(Si 1-x C x ) 3 N 4 is found to be closer to that of R-Si 3 N 4 than of R-C 3 N 4 . 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.