Modulated photocurrent measurements on icosahedral cluster solids: Boron-rich solids and aluminum-based quasicrystals

Modulated photocurrent measurements were performed on amorphous boron, beta-rhombohedral boron, and Al-Pd-Re quasicrystal. For the quasicrystal, this is the first report on photoconductivity. The data obtained for amorphous boron are analyzed by a typical model which assumes interband photocarrier generation and trap-limited conduction. Those for beta-rhombohedral boron and the quasicrystal are analyzed by a modified model which takes account of two excitation professes for carriers: (i) photoexcitation directly to conduction (or valence) band and (ii) that to localized states followed by thermal excitation into conduction (or valence) band. The results indicate that the localized states significantly contribute to photoconduction. The existence of large densities of localized states is suggested both for beta-rhombohedral boron and quasicrystals. (C) 1997 Academic Press.