Electronic and superconducting properties of silicon and carbon clathrates

We review the electronic properties of pure and doped silicon and carbon clathrates. Using accurate quasiparticle calculations within the GW approximation, we show that undoped clathrates are similar to 1.8 eV band gap semiconducting compounds. Further, the effect of doping by elements more electronegative than Si is shown to lead to p-type doped semiconductors with a similar to2.3-2.5 eV band gap in the visible energy range. Similar results are observed under doping of hydrogenated Si(n) (n = 20, 24, 28) clusters and rationalized on the basis of group theory analysis. Finally, the superconducting properties of doped clathrates are discussed. We show that superconductivity is an intrinsic property of the standard silicon sp(3) environment provided that efficient doping can be achieved. (C) 2003 Published by Elsevier B.V