X-ray photoelectron spectroscopic investigation of carbon incorporation and segregation during pseudomorphic growth of Si1−yCy on Si(001)

Abstract

An important issue for the epitaxial growth of strained Si1−yCy alloy layers is the relation between substitutional and interstitial carbon incorporation, which is strongly influenced by the growth conditions. We use in vacuu x-ray photoelectron spectroscopy (XPS) to investigate Si1−yCy layers (y<2 at. %) grown pseudomorphically on Si(001) with constant carbon and Si fluxes, but at different growth temperatures. The total carbon concentration measured by secondary-ion mass spectroscopy (SIMS) is constant in all the layers, but the amount of substitutionally incorporated carbon measured by x-ray diffraction (XRD) decreases with increasing growth temperature. The transformation of substitutional carbon atoms to carbon in interstitial Si-C defect complexes is indicated by a shift in the binding energy of the C 1s signal from 283.06 to 282.30 eV. The measured binding energy of the defect complexes leads to the suggestion that their chemical structure is very similar to that of silicon carbide. Angle-resolved XPS measurements clearly show that the carbon concentration increases toward the sample surface with increasing growth temperatures and this is interpreted to result from surface segregation of carbon atoms during growth. Interstitial carbon-containing defects are more mobile than substitutional carbon atoms. Therefore, they are probably involved in the supposed segregation. The energy barrier for the segregation process is estimated to be (0.25±0.02) eV.