Physical basis for exponential carrier trap distributions in molecular solids

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Abstract
A physical model to explain exponential carrier trap distributions in molecular solids is presented. It is considered that carrier traps are introduced by local polarization energy changes in the crystal lattice which arise from molecules being perturbed from their ideal crystal lattice positions. Molecules will be perturbed slightly or to a great extent with a range of perturbations between these extremes. In general, a greater fraction of slightly perturbed molecules will be found. In this model the relative contributions among a range of perturbed molecules will determine the trap parameter kTc If relatively large fractions of highly perturbed molecules occur, kTc will be large and a significant density of deep traps will be found. If only a small fraction of the total perturbed molecules are highly perturbed, kTc will be smaller and the majority of traps will be shallow.