Berlin 2005 – scientific programme

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HL: Halbleiterphysik

HL 61: Organische Halbleiter

HL 61.2: Talk

Wednesday, March 9, 2005, 11:00–11:15, TU P270

On the determination of the Transport Mechanism in Organic Semiconductors from the Field-Effect Mobility — •Gernot Paasch, Nabin Baran Manik, and Thomas Lindner — IFW Dresden

The field-effect mobility is determined by the gate voltage dependence of the drain current for low drain voltage. Based on fitting analytical expressions to the measured dependencies on the gate voltage and on temperature, it has been claimed that there is a one-to-one correspondence to the transport mechanism: Either hopping in a Gaussian distribution of states, or in an exponential distribution (allegedly as an approximation for the first one in some energy interval), or transport of mobile carriers above a mobility edge in the presence of exponentially distributed traps below the edge (essentially the so-called a-Si model). A critical reexamination of these procedures shows that (i) the data used to prove the assumption of hopping in exponentially distributed states can be described also with the a-Si model. (ii) The respective models should not only describe the field-effect mobility but also the subthreshold and saturation currents. (iii) Full 2D numerical simulation with the a-Si model are reported and compared (for the small drain voltage limit) to the analytic approximation. (iv) Connections with the Einstein relation and with the transition from non-degenerate to degenerate statistics are clarified.