Substitutional Ge in 3C–SiC

The incorporation of substitutional Ge into 3C–SiC alloys is studied theoretically with an anharmonic Keating model specifically adapted to the computation of the structural properties and the lattice dynamics of Si1−x−yGexCy alloys. Basic energy calculations show that the substitution of Si by Ge is more probable than the substitution of C by Ge in the zinc-blende silicon carbide crystal. If Ge replaces only Si, then the lattice parameter equals (0.43593±0.00002)+(0.000337±0.000002)y, where y stands for the Ge content. Hence, Vegard’s law is not applicable. The alloy is characterized by a distinct phonon spectrum whose maximum peak position in cm−1 is best described by the exponential decay (243±1)+(27±2)exp[−y/(7.5±1.2)] up to the zinc-blende GeC compound.