ESTIMATION OF THE MOBILITY-LIFETIME PRODUCTS IN AMORPHOUS-SILICON IN THE PRESENCE OF DISPERSIVE TRANSPORT

Applying the intuitive multiple trapping theory, we have calculated the time-of-flight (TOF) charge-collection mu tau product, (mu tau)(cc), under the condition of dispersive transport and find that (mu tau)(cc) = (1/alpha-alpha)mu(0) tau(fd)approximate to mu(0) tau(fd), where alpha is a temperature-dependent constant, mu(0) is the free-carrier mobility, and tau(fd) is the tau(fd) charge-collection free-carrier deep-trapping time. The steady-state photoconductivity mu tau product, (mu tau)(ss), is argued to be (mu tau)(ss) = mu(0) tau(fr) where tau(fr) is the steady-state free-carrier recombination lifetime. As a result, (mu tau)(ss)/(mu tau)(cc) approximate to tau(fr)/tau(fd). Our calculation shows that the presence of dispersive transport does not affect the ratio of (mu tau)(ss) and (mu tau)(cc), and that the difference between (mu tau)(ss) and (mu tau)(cc) is due almost entirely to a difference between the free-carrier recombination lifetime in the steady state and the free-carrier deep-trapping time in the TOF charge-collection experiment. The origin of the difference between (mu tau)(ss) and (mu tau)(cc) is discussed.