Assessment of the possibility of band gap widening of BaSi2 by incorporation of carbon

In order to assess the possibility of band gap widening of semiconducting BaSi2, effect of carbon incorporation into the BaSi2 lattice was evaluated by first-principle calculations. At first, structures of the equilibrium and the hypothetical BaSi2, BaC2, and BaSiC with the BaSi2 type or the CaC2 type structures are geometrically optimized and their most probable structures have been determined by energetic evaluations. As for BaC2 and BaSi2, their equilibrium structures are properly predicted. As for BaSiC, the BaSi2 type structure with the Si(5)(8d) sites substituted by carbon seems to be more favorable than (A), the BaSi2 type structure with the Si(3)(4c) and Si(4)(4c) sites are substituted by C and than (B), the CaC2 type structure. However, incorporation of C into BaSi2 seems not energetically favorable and would not proceed so much. In order to asses the case of diluted carbon concentration, dependence of the band gap on the carbon concentration was evaluated using the models of Ba(Si1−xCx)2 with the BaSi2 type structure where their Si(5)(8d) sites were partly substituted by carbon. In case compounds with x > 0.1 are formed, a band gap widening of BaSi2 can be expected.