Carbon segregation as a strain relaxation mechanism in thin germanium-carbon layers deposited directly on silicon

We report experimental evidence for the segregation and preferential localization of C atoms at the surface and substrate interfaces in thin Ge _1-xC _x, films deposited directly on Si (100). The results are interpreted in the context of C segregation providing a mechanism for strain relaxation. Four different experimental techniques, including energy-dispersive spectroscopy, electron energy loss spectroscopy (EELS), energy-filtering transmission electron microscopy, and secondary ion mass spectrometry, support our claims. The EELS analyses showed that the C bonding near the Ge _1-xC _x/Si substrate interface presented a higher sp ³ character than in the central region or at the surface. Two interpretations are given for this observation; one is that structural relaxation occurs when C atoms occupy substitutional sites in the Ge crystal closer to the Ge _1-xC _x/Si substrate interface; the other is that the higher sp ³ character of the C atoms might be an indication that C-containing tetrahedral interstitial complexes form at the interface (chemical relaxation).