ANOMALOUS TRANSIENT AND STEADY-STATE PHOTOCONDUCTIVITY STUDIES OF CANTHAXANTHIN

The growth and decay of photocurrent and its variation with temperatur e in a polycrystalline carotenoid, canthaxanthin have been studied. Th e growth of the photocurrent shows an overshoot in the growth-time cur ve before the attainment of a steady state value. Such anomalous behav iour of photocurrent is proposed to be due to much higher value of rec ombination coefficient (b(r)) than trapping coefficient (b(t)). Both f ast and slow decay of the photocurrent have been observed at different temperatures. The decay constant is found to be temperature independe nt which also suggests that trapped carrier concentration is much less than free carrier concentration. From the temperature dependence stud y it is observed that the steady state photocurrent, at first increase s with increase of temperature, attains a maximum at a particular temp erature T-max and then decreases with temperature. The variation of ph otocurrent with excitation light intensity study provides information on the carrier generation processes.