HETEROEPITAXIAL PROPERTIES OF SI1-X-YGEXCY ON SI(100) GROWN BY COMBINED ION-BEAM AND MOLECULAR-BEAM DEPOSITION

The heteroepitaxial growth of the new ternary, group-IV, semiconductor material, Si1-x-yGexCy on Si(100), has been investigated. The epitaxi al quality of Si1-x-yGexCy is found to be inferior to that of Si1-xGex with similar Si/Ge concentration ratio, grown under identical conditi ons, and the quality deteriorates with increasing C fraction. Also, th e surface roughness, as studied by tapping mode atomic force microscop y, increases with increasing C fraction as well as with increasing Ge fraction, suggesting a transition from Frank-van der Merve to Stranski -Krastanov type growth. We suggest that the very large mismatch betwee n the average bond length in the Si1-x-yGexCy material, as determined by Vegard's law, and the equilibrium Si-C bond length, weakens the Si- C bonds and reduces the elastic range of the material, thus lowering t he barrier for dislocation and stacking fault formation. The change in elasticity may also be responsible for the change in growth morpholog y, either directly by a lowered barrier for island formation or indire ctly through the formation of defects. A decrease in Ge incorporation in the Si1-x-yGexCy films with increasing C incorporation suggests a r epulsive Ge-C interaction. Moreover, we observe a C-rich, Ge-deficient precursor phase to SiC precipitates at a growth temperature of 560 de grees C, whereas at 450 degrees C no such phase can be observed. The t emperature dependence of the precursor formation is consistent with C bulk diffusion. Infrared absorption measurements cannot be used to det ect the precursor phase. Finally, the onset of epitaxial breakdown is discussed and an accurate and independent determination of the C fract ion and its substitutionality is emphasized. (C) 1997 American Institu te of Physics.