Section 7. Gap states
Cycled xerographic and time-of-flight measurements: theory and experiment

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Abstract

In this work xerographic spectroscopy is extended for an arbitrary trap distribution for both ballistic and diffusive trapping. We have investigated the dynamic equilibrium at saturation and the effect of experimental parameters on the occupation function. The relationships derived allow us to determine precisely which gap states are being mapped in a specific experiment. It is shown, that at saturation during cycled-up measurements, a quasi-Fermi level, Ef, can be defined which separates filled and empty states. A linear relationship between the cycling frequency and the saturated residual potential Vrs corresponds to traps well below Ef, where the Boltzmann distribution applies. At higher frequencies Vrs is no longer dependent on cycling and Ef moves below all traps resulting in full trap occupation. These results form the basis of a novel experiment -similar to xerographic cycling-, namely the “Cycled-Time-of-Flight” (CTOF) technique.

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