Epitaxial Growth And Electronic Characterization Of Carboncontaining Silicon-Based Heterostructures

Epitaxial Si1-x-yGexCy and Si1-yCy layers grown on Si are opening up new possibilities for bandstructure engineering of electronic devices. Thin Si1-yCy 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 Si1-x-yGexCy alloys. Although the understanding of the electronic properties of these materials is still at an early stage, interesting trends are emerging.A key issue for synthesis of these alloys is the low equilibrium solubility of carbon in silicon. However, a number of non-equilibrium methods have been employed to grow these materials. This work focuses on the properties of Si1-yCy and Si1-x-yGexCy grown by chemical vapor deposition. There is a strong influence of the growth conditions on the fraction of the total carbon concentration which is substitutional on the silicon lattice. Using low temperatures (e.g. 550°C) and very high silane partial pressures for Si1-yCy growth, good agreement is obtained between the carbon contents determined by x-ray diffraction and secondary ion mass spectrometry, for carbon concentrations up to about 1.8 atomic percent. Metal-oxidesemiconductor capacitors fabricated on Si1-x-yGexCy and Si/Si1-yCy epitaxial layers show wellbehaved electrical characteristics. Temperature dependent capacitance-voltage analysis is used to extract the band offsets, and indicates that the conduction band energy is lowered as carbon is added to Si. Complementary to the case of strained Si1-xGex grown on Si, for which most of the energy offset is in the valence band, the band offset appears primarily in the conduction band for Si1-yCy/Si heterojunctions.