Epitaxial Si_(1-x-y)Ge_xC_y and Si_(1-y)C_y layers grown on Si are opening up new possibilities for bandstructure engineering of electronic devices. Thin Si_(1-y)C_y layers containing a few atomic percent substitutional carbon, grown on Si substrates, experience biaxial tensile strain, which produces a conduction band energy splitting that is expected to be favorable for in-plane electron transport. For other applications, C may be useful as a means of compensating the compressive strain of Ge in ternary Si_(1-x-y)Ge_xC_y alloys. Although the understanding of the electronic properties of these materials is still at an early stage, interesting trends are emerging.
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