J. A. Chroboczek

Organic field-effect transistors (OFETs) suffer from limitations such as low mobility of charge carriers and high access resistance. Direct and accurate evaluation of these quantities becomes crucial for understanding the OFETs properties. We introduce the Y function method (YFM) to pentacene OFETs. This method allows us to evaluate the low-field mobility without the access or contact resistance influence. The low-field mobility is shown to be more appropriate than the currently applied field-effect mobility for the OFETs’ performance evaluation. Its unique advantage is to directly suppress the contact resistance influence in individual transistors, although such contact resistance is a constant as compared to the widely accepted variable one with respect to the gate voltage. After a comparison in detail with the transmission-line method, the YFM proved to be a fast and precise alternative method for the contact resistance evaluation. At the same time, how the contact resistance affects the effective mobility and the field-effect mobility in organic transistors is also addressed.

Abstract Conductivity, thermoelectric power, spin concentration and spin dynamics has been measured in polyaniline samples equilibrated at different pH. Data provide evidence for Metal-Insulator transition upon pH variation.

We prepared Er silicide films on (111) Si by (1) deposition of Er and contact reaction at 380 °C or (2) vacuum codeposition of Er and Si maintaining the flux ratio close to 1:2. Subsequent annealing at temperatures up to 900 °C yielded monocrystalline, continuous layers, whose properties were examined by means of low-energy electron diffraction, Auger spectroscopy (in situ) and (ex situ), x-ray and high-energy electron diffraction, and Rutherford backscattering. Method 2 was shown to give better results. The films had a hexagonal AlB2 structure with Si deficiency up to 20%, which is consistent with formerly published results on Si vacancy formation. We showed that the film structure had an additional periodicity of 15 Å along the 〈110〉 orientations of Si and of 6 Å along the 〈112〉 orientations of Si. We demonstrated a feasibility of Si reepitaxy on Er silicide deposited on (111) Si, thus fabricating a novel semiconductor/metal/semiconductor epitaxial heterostructure.

We studied electrical parallel and perpendicular transport in thin epitaxial erbium silicide films obtained by solid phase reaction and by codeposition of Er and Si on (111) Si. Resistivity measurements show that the silicide is metallic with a room-temperature resistivity of 34 μΩ cm; the dependence of the Hall coefficient on temperature can be explained by a two-band conduction model. Magnetic effects are shown to affect the low-temperature resistivity and the Hall coefficient. Perpendicular transport properties are studied by electrical [current-voltage I(V) and capacitance-voltage C(V) characteristics] and internal photoemission methods on erbium silicide/n- or p-type Si diodes. The p-type diodes have a perfect rectifying behavior with a Schottky barrier height of about 0.74 eV measured by I(V) and photoemission methods. The n-type junction is ohmic at room temperature and rectifying at low temperatures; C(V) and optical measurements yield a Schottky barrier height of about 0.28 eV. Some potential applications of erbium silicide/Si heterostructures are presented.