Central to the operation of organic electronic and optoelectronic devices is the transport of charge and energy in the organic semiconductor, and to understand the nature and dynamics of charge carriers is at the focus of intense research efforts. As a basic transport property of solids, the Seebeck coefficient S provides deep insight as it is given by the entropy transported by thermally excited charge carriers and involves in the simplest case only electronic contributions where the transported entropy is determined by details of the band structure and scattering events. We have succeeded for the first time to measure the temperature- and carrier-density-dependent thermopower in single crystals and thin films of two prototypical organic semiconductors by a controlled modulation of the chemical potential in a field-effect geometry. Surprisingly, we find the Seebeck coefficient to be well within the range of the electronic contribution in conventional inorganic semiconductors, highlighting the similarity of transport mechanisms in organic and inorganic semiconductors. Charge and entropy transport is best described as band-like transport of quasiparticles that are subjected to scattering, with exponentially distributed in-gap trap states, and without further contributions to S.

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We report on the low-temperature mobility in remotely doped p-type strained Ge layers on relaxed Si 0.3 Ge 0.7 virtual substrates, grown by low-energy plasma-enhanced chemical vapor deposition. A maximum mobility of 120 000 cm 2 V Ϫ1 s Ϫ1 has been reached at 2 K, at a carrier sheet density of 8.5ϫ10 11 cm Ϫ2 . Analysis of the mobility and Dingle ratio / q as a function of sheet density suggests that remote impurity scattering is the limiting factor at low sheet densities, but that interface impurities become more important as the sheet density increases.

We report on the dependence of the effective masses on hole density in remotely doped strained Ge layers on relaxed Si0.3Ge0.7 buffers with sheet densities from 2.9×1011 cm−2 to 1.9×1012 cm−2. The masses have been determined using temperature dependent Shubnikov–de Haas oscillations. No noticeable dependence of the mass on the magnetic field has been found. The extrapolated Γ point effective mass has been found to be 0.080 times the free electron mass. From the measured data the variation of the mass with kinetic energy and the shape of the topmost heavy hole subband have been calculated. The results are in good agreement with theoretical predictions.

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