Group IV clathrates for photovoltaic applications.

Recent studies on type-II Si/Ge clathrates for photovoltaic (PV) applications are reviewed. The band-gap energies (E_g) experimentally estimated for Si and Ge clathrates are discussed on the basis of the comparison with theoretical calculation. For the Si and Ge clathrates, E_g = 1.7–1.9 and 0.6–0.8 eV are acceptable values, respectively. Thin films of type-II Si clathrates have been successfully synthesized on Si wafers. A device was fabricated using a Si clathrate thin film, and its PV response was observed. For the Ge clathrate, a single-crystal-like thin film was identified to epitaxially grow on a Ge(111) wafer. The PV response and epitaxial growth of group IV clathrates found in recent studies strongly suggest that these new materials will be the next-generation platform for semiconductor technology. [ABSTRACT FROM AUTHOR]