ELECTRONIC-STRUCTURES OF SI1-XCX AND SI1-X-YCXGEY ALLOYS

The linear-muffin-tin-orbital method with the atomic-sphere approximation is used to study the electronic structures of Si1-xCx and Si1-x-yCxGey alloys. The dependence of minimum band gap Eg, electronic density of states, and valence-band width on alloy composition is investigated. All inequivalent atomic configurations for each given alloy composition are considered. It is found that the electronic structures of Si1-xCx and Si1-x-yC xGey show an unexpected variation of band gap versus the carbon concentration: For small to moderate concentrations of C in Si 1-xCx and Si1-x-0.125CxGe 0.125, the band gap decreases from that of pure Si. The lattice relaxation does not change such character of Eg. The peak positions in density of states shift downward as the carbon concentration in Si 1-xCx and Si1-x-0.125CxGe 0.125 increases; meanwhile, the valence band is monotonically widened. © 1995 American Institute of Physics.