Field Dependence Of Activation Energy Research Articles

Hole transport in isopropyl carbazole—polycarbonate mixtures

Abstract The hole mobility μ has been measured in dispersions of N-isopropyl carbazole in polycarbonate for relative concentrations c between 100% (PVK) and 2%. At sufficiently high temperature (T) and field (F), transport is essentially coherent. For c 10%, μαR 2exp(− 2αR), where R is the average carbazole spacing and α≃0·62× 108cm−1, almost independent of T and F. For c<5% and high T and F, μ becomes substantially greater than predicted by the above relation. At constant T, logμ is proportional to F 1/2 rather than to F. At constant F, an approximate fit to a relation μα exp [−(T 0/T)2] is obtained, but systematic deviations suggest an apparently field-dependent activation energy of about 0·35 eV at F = 0. These observations are interpreted in terms of field-enhanced polaron tunnelling, leading, in first approximation, to a Poole-Frenkel-like behaviour of μ.

Magnetic field dependence of activation energies in the fractional quantum Hall effect.

We have studied the temperature dependence of the fractional quantum Hall effect at Landaulevel filling factors $\ensuremath{\nu}=\frac{1}{3}, \frac{2}{3}, \frac{4}{3}, \frac{5}{3}, \frac{2}{5}, \mathrm{and} \frac{3}{5}$ in magnetic fields up to 28 T to determine the magnitude of the associated energy gaps. The data suggest a single activation energy for $\ensuremath{\nu}=\frac{1}{3}, \frac{2}{3}, \frac{4}{3}, \mathrm{and} \frac{3}{5}$. Its magnitude, much smaller than predicted by current theories, vanishes for $B\ensuremath{\lesssim}6$ T and saturates at $B\ensuremath{\gtrsim}18$ T. The data also suggest a single activation energy for $\ensuremath{\nu}=\frac{2}{5} \mathrm{and} \frac{3}{5}$ which is smaller than predicted.

Total Dose Hardness Assurance Implications of Field-Sensitive Interface States

We have observed the generation of interface states in SiO2 MOS capacitors that are field-and time-dependent as well as thermally activated. The number of interface states generated is linearly dependent on the applied field with a threshold field for occurrence. There is a t1/4 time dependence for interface state generation. The generation of these field-sensitive interface states is thermally activated with a field-dependent activation energy. A model based on oxygen-derived defects in SiO2 is proposed to explain the data. Finally, strong correlation has been found between these metastable interface states and the radiation hardness of the MOS devices.

On the Thermal Activation Energy for High-Field Electric Conduction in Dielectric Liquids

Taking into account the combined electrode and bulk effects, an expression for the high-field filamentary conduction as a function of applied field and temperature for dielectric liquids has been derived. This expression can explain recent experimental results on the field-dependent thermal activation energy for electric conduction in hydrocarbon liquids.

Theory of thermally stimulated current in hopping systems

Using the concept of thermally activated mobility, a theory is developed to calculate the thermally stimulated current (TSC) in hopping systems as a function of temperature. Unlike the existing theories which describe only the band transport systems, the present theory is applicable to both band and hopping transport systems. Various features of this ’’mobility-induced’’ TSC are illustrated with numerical examples and compared with experiments performed on polymer films (e.g., PVK). These features form the basis of a new method (reported in an earlier paper) for determination of the activation energy, and a technique for studying very low mobilities and/or very low field transport phenomena. It is also found that an observation of shift in TSC peak temperature with applied field does not necessarily imply a field-dependent activation energy.

A New High-sensitivity Organic Photoconductor for Electrophotography

A new organic photoconductor has been developed, consisting essentially of a 1:1 molar ratio of one molecule of 2, 4, 7- trinitro-9-fluorenone (TNF) to one monomer unit of poly-N-vinylcarbazole (PVCz). This photoconductor (1:l TPC) is nearly panchromatic int he visible range of the spectrum and has white-light sensitivity approximately equal to that of amorphous selenium when used for electrostatic imaging. The photosensitivity, which is due mainly to the TNF-PVCz complex, is greater for negative corona charging than for positive charging. Charge acceptance of the 1:1 TPC is high, ≅ 1200 volts for a 13µm film, indicating good dielectric strength. Dark decay of the charge is affected by substrate materials and substrate surface conditions. In general dark decay is slower for negative charging than for positive charging. Quantum efficiency (Q. E.) is nominally about 0.15 in the range of 400 to 500 nm but decreases somewhat for shorter and longer wavelengths. The Q.E. increases rather markedly with field strength, but decreases somewhat at high light intensities. Field-controlled photogeneration of carriers is indicated, and thermal measurements show a field-dependent activation energy in the range of 0.06 to 0.20 eV. The absence of residual potentials in light decay curves and the lack of a thickness effect in photodischarge currents indicate that no deep traps are present in the 1:1 TPC layers.

Electrical Conduction Mechanism in Ultrathin, Evaporated Metal Films

The electrical conduction mechanism in the film plane of ultrathin, evaporated metal films was investigated. These films consist of a planar array of many small discrete islands. The conduction process consists of, first, charge carrier creation which is thermally activated and involves charge transfer between initially neutral particles, and, second, the drift velocity of these charges in an applied field. Charge transfer between particles occurs by tunneling. The following features were predicted and can be verified experimentally: the conductivity depends exponentially on reciprocal temperature, and it should be independent of field at low fields. Deviations from the exponential temperature dependence can be understood in terms of a spectrum of activation energies, while deviations from Ohm's law at high fields can be explained readily in terms of a field dependent activation energy.