STABILIZING THE SURFACE-MORPHOLOGY OF SI1-X-YGEXCY SI HETEROSTRUCTURES GROWN BY MOLECULAR-BEAM EPITAXY THROUGH THE USE OF A SILICON-CARBIDESOURCE/

Si1-x-yGexCy/Si superlattices were grown by solid-source molecular bea m epitaxy using silicon carbide as a source of C. Samples consisting o f alternating layers of nominally 25 nm Si1-x-yGexCy and 35 nm Si for 10 periods were characterized by high-resolution x-ray diffraction, tr ansmission electron microscopy (TEM), and Rutherford backscattering sp ectrometry to determine strain, thickness, and composition. C resonanc e backscattering and secondary ion mass spectrometries were used to me asure the total C concentration in the Si1-x-yGexCy layers, allowing f or an accurate determination of the substitutional C fraction to be ma de as a function of growth rate for fixed Ge and substitutional C comp ositions. For C concentrations close to 1%, high-quality layers were o btained without the use of Sb-surfactant mediation. These samples were found to be structurally perfect to a level consistent with cross-sec tional TEM (<10(7) defects/cm(2)) and showed considerably improved hom ogeneity as compared with similar structures grown using graphite as t he source for C. For higher Ge, and C concentrations, Sb-surfactant me diation was found to be required to stabilize the surface morphology. The maximum value of substitutional C concentration, above which exces sive generation of stacking fault defects caused polycrystalline and/o r amorphous growth, was found to be approximately 2.4% in samples cont aining between 25 and 30% Ge. The fraction of substitutional C was fou nd to decrease from roughly 60% by a factor of 0.86 as the Si1-x-yGexC y growth rate increased from 0.1 to 1.0 nm/s. (C) 1998 American Vacuum Society.