Analysis of Trap Distribution Using Time-of-Flight Spectroscopy

Abstract

A new analytical method for determining trap distribution from a transient photocurrent in time-of-flight (TOF) measurements has been proposed in the context of convection diffusion equation with multiple-trapping and detrapping processes. The method does not need, in principle, data on temperature dependence and any initial assumption about the form of trap distribution. A trap distribution is directly extracted from time profiles of transient photocurrents on assuming the Einstein relation between mobility and diffusion constant. To demonstrate the validity of the method, we first applied photocurrents that were prepared in advance by random walk simulation for some typical trap distributions assumed. Then, we attempt to determine a trap distribution for a particular mesophase of a liquid crystal of phenylnaphthalene derivative, for which the temperature dependence of carrier transport properties is hardly available. Indeed, we have obtained an extrinsic shallow trap distribution at about 200 meV in depth together with a tail-shaped Gaussian-type density-of-states distribution. Thus, we conclude that the method may be a powerful tool to analyze a trap distribution for a system that exhibits temperature-sensitive conformational changes and/or whose carrier transport properties are not available as a function of temperature.

Phase transition, optical and photoconductive properties of bay-substituted benzoporphyrin derivatives

“…32 These features have been well explained by a narrow distribution of density, ranging from 40 to 60 meV comparable to kT, where T is the temperature for the TOF experiments. 33 Also, the hole mobility of TBP and TBMAP as a function of the electric eld is illustrated in Fig. 7b.…”

Solutions of q-deformed multiple-trapping model (MTM) for charge carrier transport from time-of-flight transient (TOF) photo-current in amorphous semiconductors

“…The films include amorphous inorganic or organic semiconductors, with adequate supposition of trapping and releasing parameters in the form of continuous distribution of trap states such as an exponential distribution e −E/k B T , a Gaussian distribution or other shapes of trap distribution. However, this method is applicable only when a shape of the trap distribution is appropriately taken to describe the distribution of localized states playing the major role in trapping events [12].…”