Control of composition and crystallinity in the molecular beam epitaxy of strain-compensated Si1-x-yGexCy alloys on Si

In this paper, we present a mass-spectrometry-based approach to the control of C concentration during molecular beam epitaxy (MBE) of Si1-x-yGexCy/Si superlattices. High-resolution X-ray diffraction, ion beam analysis, and transmission electron microscopy (TEM) were used to characterize composition and crystallinity in a series of superlattices for which the average strain condition was designed to range from biaxial compression to biaxial tension. For each sample, secondary ion mass spectrometry and Rutherford backscattering spectrometry confirmed that the average composition of each Si1-x-yGexCy layer was constant during growth. However, TEM revealed strain contrast variations within the Si1-x-yGexCy layers, leading to the conclusion that the presence of C on the wafer surface leads to laterally inhomogenous incorporation of C (and possibly Ge). TEM also showed that all samples were essentially free of extended defects except for short microtwins observed in the tensile-strained sample, that originated in the Si1-x-yGexCy lavers and terminated in the Si lavers directly above.