Growth and characterization of Ge1 − yCy/Si superlattice structures on Si substrates

The growth of short-period Ge1 − yCy/Si superlattice structures by solid-source molecular beam epitaxy on (001) Si substrates is investigated. High quality strained Ge1 − yCy alloy layers with a typical C content of 5% and a thickness up up to 7 Å are grown at a substrate temperature of about 250°C. Transmission electron microscopy shows a high interface quality which is well comparable to Ge/Si structures. No lattice defects are observed. X-ray diffraction reveals a strong strain compensation of about 45% in Ge0.954C0.046 layers as compared to pure Ge layers. The diffraction data agree with simulation results which are based on Vegardʹs law and on linearly interpolated elastic moduli. The phonon modes observed by Raman spectroscopy indicate well defined Ge1 − yCy layers. After annealing at temperatures up to about 750°C the Ge1 − yCy layers show a slightly lower threshold for interdiffusion and an improved stability for lattice relaxation, compared to pure Ge layers.