MODULATED PHOTOCURRENT MEASUREMENTS ON ICOSAHEDRAL CLUSTER SOLIDS - BORON-RICH SOLIDS AND ALUMINUM-BASED QUASI-CRYSTALS

Modulated photocurrent measurements were performed on amorphous boron, beta-rhombohedral boron, and Al-Pd-Re quasicrystal. For the quasicrys tal, this is the first report on photoconductivity. The data obtained for amorphous boron are analyzed by a typical model which assumes inte rband photocarrier generation and trap-limited conduction. Those for b eta-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) t hat to localized states followed by thermal excitation into conduction (or valence) band. The results indicate that the localized states sig nificantly contribute to photoconduction. The existence of large densi ties of localized states is suggested both for beta-rhombohedral boron and quasicrystals. (C) 1997 Academic Press.