Field effect

About: Field effect is a research topic. Over the lifetime, 4018 publications have been published within this topic receiving 92613 citations.

Field Effect on the Singlet and Triplet Exciton Formation in Organic/Polymeric Light-Emitting Diodes

Abstract: Recently, both experimental and theoretical evidence indicate that the electrically-generated singlet and triplet exciton formation ratio (r S / T ) in conjugated polymers can exceed the 1:3 spin statistics limit. However,the extent that the electric field influences r S / T is in controversy. By measuring the rates of photo- and electro-phosphorescence and fluorescence, Wilson et al. 6 concluded that the ratio r S / T is independent of the external electric field; Lin et al. 8 found that the ratio increases monotonically with the electric field by measuring the relative densities of singlet and triplet exciton in EL and PL processes; from a quantum-dynamical calculation, Tandon et al. 1 1 observed an abrupt increase in the ratio with respect to the electric field. In this work, we apply a correlated quantum-chemical approach coupled with a first-order perturbation, to investigate the relationship between the formation ratio and the electric field. We have calculated the influences of the electric field on the singlet and triplet exciton states as well as on the electron-hole free pair (charge-transfer) state. It is found that for p-phenylene-vinylene oligomer, the formation ratio of singlet excitons with respect to triplet excitons increases with the electric field.

Dielectric and field-induced strain behaviour of (Pb1−xBax) ZrO3 ceramics

Abstract: The effects of Ba2+ substitution on the dielectric properties and induced strain behaviour of the (Pb1−xBax) ZrO3 ceramics (0.05≤x≤0.3) have been investigated as a function of x. A new phase diagram of the (Pb1−xBax) ZrO3 system, indicating the field effect on the phase transition, is also presented. As the Ba2+ content increases, the Curie temperature decreases linearly, whereas maximum dielectric constant increases for up to 20 mol% Ba2+ addition, and then decreases with further Ba2+ addition. Based on the hysteresis loops, the temperature range of the ferroelectric phase as an intermediate phase between the antiferroelectric and paraelectric phases, increases with increasing electric field and Ba2+ content. The ferroelectric loops are induced at room temperature for the specimens containing above 10 mol% Ba2+ by applying an electric field up to ∼25 kV cm−1. However, for the 5 mol% Ba2+-substituted specimen, no ferroelectric loop is induced, even with applied fields up to 55 kV cm−1. The phase transition due to electric field and Ba2+ addition is also confirmed by the measurement of the field-induced longitudinal strain.

Combined measurements of field effect, surface photo-voltage and photoconductivity

Abstract: Combined measurements have been made of surface recombination velocity, surface photo-voltage, and the modulation of surface conductance and surface recombination velocity by an external field, on etched germanium surfaces. Two samples, cut from an n-type and a p-type crystal of known body properties, were used, the samples being exposed to the Brattain-Bardeen cycle of gaseous ambients. The results are interpreted in terms of the properties of the surface space-charge region and of the fast surface states. It is found that the surface barrier height, measured with respect to the Fermi level, varies from −0.13 to +0.13 volts, and that the surface recombination velocity varies over about a factor of ten in this range. From the measurements, values are found for the dependence of charge trapped in fast surface states on barrier height and on the steady-state carrier concentration within the semiconductor.