K. Mattenberger

Oxygen-related traps in pentacene thin films : Energetic position and implications for transistor performance

We studied the influence of oxygen on the electronic trap states in a pentacene thin film. This was done by carrying out gated four-terminal measurements on thin-film transistors as a function of temperature and without ever exposing the samples to ambient air. Photo-oxidation of pentacene is shown to lead to a peak of trap states centered at 0.28 eV from the mobility edge, with trap densities of the order of

Defect healing at room temperature in pentacene thin films and improved transistor performance.

{10}^{18}\text{ }{\text{cm}}^{\ensuremath{-}3}

HoAs: a model compound for the cooling by the barocaloric effect

. As the gate voltage is ramped up, these trap states are occupied at first and cause a reduction in the number of free carriers at a given gate voltage. Moreover, the exposure to oxygen reduces the mobility of the charge carriers above the mobility edge. We correlate the change of these transport parameters with the change of the essential device parameters, i.e., subthreshold performance and effective field-effect mobility. This study supports the assumption of a mobility edge for charge transport and contributes to a detailed understanding of an important degradation mechanism of organic field-effect transistors. Deep traps in an organic field-effect transistor reduce the effective field-effect mobility by reducing the number of free carriers and their mobility above the mobility edge.

Neutron scattering and magnetization studies of plutonium monochalcogenides

We report on a healing of defects at room temperature in the organic semiconductor pentacene. This peculiar effect is a direct consequence of the weak intermolecular interaction which is characteristic of organic semiconductors. Pentacene thin-film transistors were fabricated and characterized by in situ gated four-terminal measurements. Under high vacuum conditions (base pressure of order

Direct link between low-temperature magnetism and high-temperature sodium order in NaxCoO2.

{10}^{\ensuremath{-}8}\phantom{\rule{0.3em}{0ex}}\mathrm{mbar}

The extraordinary case of CeSb

), the device performance is found to improve with time. The effective field-effect mobility increases by as much as a factor of 2 and mobilities up to

Measurement of giant magnetic anisotropy in a uranium compound

0.45\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{V}\phantom{\rule{0.2em}{0ex}}\mathrm{s}

Melting of the Na layers in solid Na0.8CoO2.

were achieved. In addition, the contact resistance decreases by more than an order of magnitude and there is a significant reduction in current hysteresis. Oxygen and nitrogen exposure as well as annealing experiments show the improvement of the electronic parameters to be driven by a thermally promoted process and not by chemical doping. In order to extract the spectral density of trap states from the transistor characteristics, we have implemented a powerful scheme which allows for a calculation of the trap densities with high accuracy in a straightforward fashion. We show the performance improvement to be due to a reduction in the density of shallow traps

High temperature susceptibilities of actinide monopnictides and monochalcogenides

\ensuremath{\leqslant}0.15\phantom{\rule{0.3em}{0ex}}\mathrm{eV}

Tetrathiofulvalene and tetracyanoquinodimethane crystals: Conducting surface versus interface

from the valence band edge, while the energetically deeper traps are essentially unaffected. This work contributes to an understanding of the shallow traps in organic semiconductors and identifies structural point defects within the grains of the polycrystalline thin films as a major cause.