Growth and strain compensation effects in the ternary Si1−x−yGexCy alloy system

Abstract

Strain compensation is an important aspect of heterostructure engineering. In this letter, we discuss the synthesis of pseudomorphic Si_1−yC_y and Si_1−x−yGe_xC_y alloy layers on a silicon (100) substrate by molecular beam epitaxy using solid sources and the controlled strain compensation that results from the introduction of the ternary system. The introduction of C into substitutional sites in the crystal lattice is kinetically stabilized by low‐temperature growth conditions (400–550 °C) against thermodynamically favored silicon‐carbide phases. The lattice constant in Ge is about 4% larger than in Si, whereas in diamond it is 52% smaller. Consequently, the compressive strain caused by 10.8% Ge in a pseudomorphic Si_1−xGe_x alloy can be compensated by adding about 1% carbon into substitutional lattice sites of the film assuming Vegard’s law of linear change of the lattice constant in the alloy as a function of the composition. Using x‐ray diffraction, we observe a partial strain compensation in Si_0.75−yGe_0.25C_y alloys on Si depending on the amount of carbon in the layer, with no observable misfit dislocation generation. The Raman spectra from Si_1−yC_y and Si_1−x−yGe_xC_y alloys show a substitutional carbon vibration mode at about 600 wavenumbers. No indication of silicon‐carbide precipitation is observed in transmission electron microscopy and Raman spectroscopy.