Berlin 2005 – scientific programme

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HL: Halbleiterphysik

HL 61: Organische Halbleiter

HL 61.3: Talk

Wednesday, March 9, 2005, 11:15–11:30, TU P270

Space Charge Layers in Organic Semiconductors with Gaussian or Exponential Density of States — •Susanne Scheinert¹ and Gernot Paasch² — ¹TU Ilmenau — ²IFW Dresden

Space charge layers (SCL) in MOS structures are decisive for the operation of field effect transistors (FET). For many organic semiconductors, transport takes place as hopping in Gaussian or exponentially distributed states. However, existing theoretical descriptions of SCL suppose a density of states other than a Gaussian or an exponential. We present results of a simulation study for a thin semiconducting layer e.g. on a metal substrate and the MOS structure as the basic module of the FET. From the calculated distributions of concentration, field and potential, and the semiconductor capacitance as a function of either the surface potential or an applied gate voltage detailed, conclusions are drawn. Of special importance are: (i) the bulk Fermi energy and hence the flat band voltage depend strongly on the distribution, (ii) for broader distributions the accumulation layer becomes thinner, (iii) this can lead to an apparent contribution to a surface dipole, (iv) the total areal charge, which determines the FET current, is almost the same as that one of a delta shaped distribution if the flat band voltage shift is considered appropriately.