Concentration Of Trapping Centers Research Articles

The Effect of Density and Concentration of Trapping Centers on Charge Carrier Mobility in Polymer Dielectrics

The spectra of the currents of thermostimulated depolarization and the time dependences of the electret potential difference were measured in polymers irradiated with soft X-rays of electric gas discharge. The results of measurements are used to determining the mobility of electrons and holes in polymer cable and capacitor dielectrics having different values of density and concentration of electrically active trapping centers.

Enhanced blue mechanoluminescence of SrnMgSi2O5+n:Eu alkali-earth silicate induced by defective phase

Obvious enhancement of blue mechanoluminescence (ML) has been observed for SrnMgSi2O5+n:Eu (1 ≤ n ≤ 2) (SMSE) fabricated via systematically controlling the defective phases. The existence of defective phases affects not only the concentration of trap centers but also the structure of SMSE. The dependence between ML intensity and thermoluminescence integrated intensity showed that the trap centers created by defective phase play an important role in producing the ML of SMSE. Furthermore, when the effect of trap centers on ML eliminated to the smallest, the sample with the easiest deformation structure possessed the highest ML intensity. The strong piezoelectric ability induced by the existence of defective phase is responsible for this phenomenon. These results indicate that the origin of ML is piezoelectricity-induced electroluminescence, that is, piezoelectricity impelled the trapped electrons to escape from the traps and produce ML.

Improvement of the scintillation properties of Gd3 Ga3 Al2 O12 :Ce,B single crystals having tailored defect structure

A novel approach is reported to minimize various defect centers in Ce doped Gd3Ga3Al2O12 single crystals to improve the scintillation properties. The crystals of Gd3Ga3Al2O12 codoped with 0.2 at% Ce and B (GGAG:Ce,B) have been grown in air and argon ambient using the Czochralski technique. The scintillation light output of crystals grown in Ar ambient was significantly increased after annealing the crystals in air. The measured light output of 60000 ph/MeV for annealed crystals is the highest value reported among this class of materials. As a consequence, the energy resolution at 662 keV gamma-rays from a 137Cs source was improved from 8% for the crystals grown in air to 6% for crystals grown in Ar and subsequently annealed in air. Further, the thermal quenching energy of photoluminescence (PL) emission was increased to be 470 meV for the annealed crystals. The thermoluminescence (TL) measurements suggest that the crystals grown in Ar ambient and post-growth annealed in air may have a lesser concentration of trap centers which subsequently lead to the improvement in optical and scintillation properties leading to a superior detector performance. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Dark current mechanisms in stabilized amorphous selenium based n-i detectors for x-ray imaging applications

The dark current behavior under operating bias is one of the important selection criteria for an x-ray photoconductor to be usable in a practical x-ray image detector. The authors have developed an analytical model for describing the transient and steady-state behavior of dark current in n-i-type amorphous selenium (a-Se) detectors by considering carrier injections from the metal contacts and thermally generated carriers. It has been found that the thermal generation current is almost two orders of magnitude smaller than the total steady-state dark current in n-i-type a-Se detectors. The main source of dark current is the injection of holes from the metal/n-layer interface which is described by the diffusion theory. The hole injection from the metal depends on the blocking layer (n-layer) thickness, the concentration of trap centers in the blocking layer, the characteristic carrier release time, and the effective barrier height. The fitting of the first principles model with the experimental results estimates the concentration of deep hole trap center in the n-layer, the trap depth from the valence band edge, and the effective barrier heights for the injecting carriers. The electron injection varies with the work function of the contact metal.

An insight into the localization of charge carriers in conducting polyaniline by analyzing thermally stimulated depolarization signals

A dielectric relaxation mechanism, which is attributed to the localized motion of trapped polarons, has been recorded in conducting polyaniline by employing the thermally stimulated depolarization current technique. The signal was analyzed within the frame of the normal distribution in the activation energy value. The experimental dielectric relaxation results were manipulated in order to evaluate the length of the jump distance that the trapped polarons transfer along and the concentration of trap centers. The concentration of trapped carriers is calculated from two different viewpoints: the pair approximation that assumes phonon-assisted tunneling through the barrier separating two adjacent sites and the pinning model that considers the trapped polaron oscillating around its pinning point. Both models provide compatible results.

La-Doped BaTiO<sub>3</sub> Ceramics with Bi<sub>2</sub>O<sub>3</sub> as a Grain Boundary Element

It is known that sintered bodies of semiconducting barium titanates or its solid solutions have a large positive temperature coefficient of resistivity above and near the Curie temperature. They have a negative temperature coefficient of resistivity normal as usual semiconductors below the Curie temperature. At the Curie temperature the tetragonal to cubic transition takes place and the resistivity anomaly around the temperature has been related to the transition. At the transition temperature, orthorhombic to tetragonal, however, no anomaly in the resistivity-temperature characteristic has been found on the sintered bodies reported so far.The present authors modified the texture of sintered bodies of semiconducting barium titanate with bismuth oxide penetrated along grain boundaries. When non-ohmic contact electrodes were applied to the texture modified specimens another anomaly in the resistivity-temperature characteristic appeared above the orthorhombic to tetragonal transition temperature in addition to the anomaly above the Curie temperature. The nonlinear current-voltage and capacitance-voltage characteristics measured on present specimens with asymmetric electrodes (non-ohmic contact electrode to the one side and ohmic contact to the other side), showed the existence of a surface barrier-layer in the interface between the non-ohmic electrode and the body with texture modified. The nonlinear curve in the capacitance-voltage characteristic was not expressed by the relation 1/C2=2(Vd-V)/eεsNd (Vd is a built-in voltage at a barrier, εs is a dielectric constant in a barrier-layer and Nd is the density of ionized donor centers) above a certain reverse bias which was dependent on a measuring temperature. It seems reasonable to assume that the surface barrier-layer is made up of a inversion layer and a bismuth oxide layer. The barrier gave rise to the anomaly around a room temperature. Under a higher electric field the effect of the surface barrier becomes negligible small compared with the effects by barriers given across the grain boundaries in the sintered body which is considered to give rise to the anomaly above the Curie temperature. It may be considered that by the addition of bismuth oxide the concentration of trap centers changed; the concentration of trap centers affects the height and width of the barrier between semiconducting grains and of the barrier between the non-ohmic electrode and the pellet surface.