Abstract
This article reviews the electronic states and the optical properties of silicides with unique arrangements
of Si atoms, ternary Si clathrates K8Ga8Si38 and barium disilicide BaSi2. K8Ga8Si38 is a type-I clathrate,
in which Si/Ga atoms form a cage framework that consists of face-shared (Si/Ga)20 dodecahedra and (Si/
Ga)24 tetrakaidecahedra and where K atoms are located inside the polyhedra as guests. K8Ga8Si38 is an
indirect gap semiconductor with a band gap of 1.2 eV. BaSi2 crystallizes in the BaSi2-type structure,
where Si atoms form Si4 tetrahedra. BaSi2, an indirect band gap semiconductor with a band gap ranging
from 1.1 to 1.3 eV, is attracting industry attentions as a thin-film solar cell material. We discuss why
BaSi2 has a large optical absorption coefficient near the absorption edge despite its indirect band gap
semiconductor.
