We investigated in detail the strain relaxation behaviour of metastable tensile-strained Si 1−y C y epilayers on Si(001) by comparing the layers before and after an annealing step using a variety of different diagnostic methods. The dominant strain-relieving mechanism is the formation of carbon-containing interstitial complexes and/or silicon carbide nanoparticles, similar to the behaviour of carbon in silicon under thermodynamical equilibrium conditions (concentrations below the solid bulk solubility limit). We did not observe any carbon out-diffusion. To grow material suitable for device applications, all carbon atoms should be incorporated substitutionally. There is only a very narrow temperature window for perfect epitaxial growth of such layers, limited on one side by the possible formation of interstitial carbon complexes and on the other side by the deterioration of epitaxial growth at low temperatures. The carbon concentration should not exceed a few per cent to avoid strain-driven precipitation.
We report on x-ray diffraction measurements of the substitutional carbon content y in pseudomorphic Sir -,,CY (ycO.02) layers grown on (lOO)-oriented silicon substrate. The samples were grown by molecular beam epitaxy and investigated during post growth annealing in situ by an x-ray powder diffractometer. Despite the tensile strain in the 100-nm-thick layers and the high carbon supersaturation, the samples were stable up to 800 "C. Beyond this temperature range, the substitutional carbon content decreased exponentially during isothermal annealing. This effect can be explained by the precipitation of the carbon and the nucleation and diffusion limited growth of Sic nanocrystals. Since no strain relief by the introduction of misfit dislocations was detectible, we conclude that contrary to the mechanism of strain relief in Sit-,Ce,, in comparably strained Sit -,,CY epilayers, the main high temperature process is precipitation. 0 199.5 American Institute of Physics.
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