Modulated photocurrent measurements on pure and V-doped β-rhombohedral boron

The modulated photocurrent method has been applied to pure and vanadium (V)-doped beta -rhombohedral boron (beta -B) with the goal of investigating the difference in the distribution of electronic states in the band gap between them, Excitation light intensity dependence of the amplitude and phase shift of photocurrent shows that V-doped beta -B has a much larger trapping states density for photoexcited carriers than pure beta -B, With increasing temperature, the amplitude increases and decreases for pure and V-doped beta -B, respectively, indicating that the conduction mechanism for photoexcited carrier is completely different between the two samples. The unusual negative temperature dependence for V-doped beta -B is similar to that for Al-Pd-Re quasicrystal and the change of dependence from positive to negative is consistent with the approach to aluminum-based icosahedral quasicrystals in atomic structure and in transport properties by V-doping to beta -B, The modulated frequency dependence of the amplitude and phase shift cannot be explained by the usual photoconduction processes, which are indicating that the gap states distribution and photoconduction processes in these materials are complicated. (C) 2000 Academic Press.