Fukuzo Yoshida

On the Determination of the Trap Depths from Thermally Stimulated Currents II

A new asymptotic estimation method (the H-method), which enables one to estimate the exact energy depth Et of a trap from the TSC peak and one of other coordinates of the higher side of the peak temperature Tp, has been proposed. From the establishment of this proposal and the L-method estimated from the lower side, more exact estimation of Et and a new application were made possible. The m characteristics that provide a basis for judging whether a TSC curve is contributed by a single trap only or by multiple traps have been reported. They show a perfect flatness with the same Et value in the range from ca. 10% to 90% of 1/m if the TSC curve is contributed by a single trap only. The m characteristics of the coefficient Ci (=Et/kTp) have been proposed. A simple and convenient equation of the H-method and an expression of the asymptotic estimation method without Tp are presented.

New exact computer analysis of the TSC curve by the asymptotic estimation method and an approach to the electrical conduction of organic crystals

Experimental results were obtained for a naphthacene-doped anthracene single crystal excited by Q-switched ruby laser pulses. Two representative TSC (thermally stimulated current) curves were obtained. The curves were analyzed by an asymptotic estimation method, involving the autoseparation of the TSC curve and the exact estimation of the energy depth of the carrier trap from the separated curve.<<ETX>>

TSC of polyaniline thin film

We report the results of thermally stimulated current (TSC) measurements of polyaniline thin films with electric conducting or insulating property and the latest application of the analytical estimation methods for TSC signals.

Charging property and charge trap parameters in porous polypropylene film using thermally stimulated current

The heat resisting property of charge storage resins is required. It is well known that the charge storage of a polymer is influenced by the charge carrier traps. Charge trap parameters and charging property of porous and solid polypropylene (PP) films were studied using thermally stimulated current (TSC). We proposed already the Asymptotic Estimation Method (AEM) to evaluate trap parameters such as the energy depth of the trap Et and the escape frequency factor ν from TSC spectrum caused by multiple carrier traps, separately. To describe the ν- Et correlation, the trap sites caused by the porous structure were evaluated in the range of 1.0–1.1 eV. In addition, the ν values for those trap sites were found to be in the range 1011–1012 S−1. A comparison of surface potential decay revealed that drawing treatment caused discharge property by heating and the porous structure in the PP film induced charge storage stability.

Autoseparation of thermally stimulated currents and exact estimation of energy depths of their carrier traps

A new important concept which enables one to separate observed TSC curves automatically and estimate energy depths of carrier traps from the separated TSC curves by computer has been reported. In this proposal, our asymptotic estimation method, which can estimate the energy depth of the carrier trap exactly and simply, also enables one to characterize self-convergence by the repetition of the computer simulation processes.

A behaviour of trapped carrier excited by different wavelengths of illumination

A thermally stimulated current has been observed in anthracene single crys tal of organic material. The specimen was excited at various temperatures by laser light with different wavelengths of 2.08 eV, 2.33 eV and 1.79 eV. As the illumination temperature rises, several orders of decrease in the escape frequency factor v of a carrier trap have been confirmed through exact estimation of the energy depth.

Influence of heat-treatment of traps examined by using the thermally stimutated current and the dielectric characteristics of carbon-black-filled polyimide film

The influence of heat-treatment on the thermal deterioration of carbon-black-filling polyimide film (CBPI film) was examined by thermally stimulated current (TSC) measurement. CBPI film used for experiment had about 0.01 of tan δ and about 5.7 of relative permittivity. The conductivity of the film was about 1016 S/cm and was stable for a temperature change. When CBPI film was heat-treated, the conductivity became thermal active form. The thermal deterioration of a carbon black structure was occurred, because the tan δ was increased about 20 times in comparison with that of the film before the heat-treatment. Four kind of charge traps were also observed in the TSC spectrum of the CBPI film.

Evaluation of defect levels formed in the nano-porous titanium oxide layer of dye-sensitized solar cell

The development of the dye-sensitized solar cell (DSC) has been expected to supply another solar cell other than the silicon solar cells, for its convenient production processes. The nano-porous titanium oxide (TiO2) layer, photo-electrode of DSC, is constructed on a F-doped SnO2 transparent electrode(FTO), before the dye deposition. The structure of the porous TiO2 layer, such as the existence of charge traps, seems to influence the photoelectric conversion efficiency of DSC. The possibility of estimating the photo-electrode efficiency by the charge trap structure was studied with thermally stimulated current (TSC) measurement. As a result of the TSC measurement, four charge traps were detected in the electrode and were evaluated the energy trap depths of 0.07 eV, 0.138 eV, 0.385 eV and 0.381 eV. The escape frequency factors were also evaluated in large span from 10 s-1 to 108 s-1.

Evaluation of energy depth of traps in PA/BaTiO3 composite film by TSC measurements

Recently, composite films of polymer and inorganic-filler are required as a key material for further downsizing of electronic devices such as a capacitor. We have studied, through thermally stimulated current (TSC) measurement, to explain the effects of trap levels on electrical conduction and charging properties of Polyamide(PA)/BaTiO<inf>3</inf> composite films. TSC measurements were performed from 150 K to 350 K. TSC signals were detected for PA, 20 vol% filled PA, and 40vol% filled PA. Trap parameters were accurately evaluated through asymptotic estimation method (AEM). The values of energy depth of charge trap (E<inf>t</inf>) for PA, 20 vol% filled PA, and 40vol% filled PA were estimated 0.654 eV, 0.647 eV, and 0.625 eV, respectively. Escape frequency factors (υ) were also estimated 5.28 × 10⁸ S⁻¹, 1.87 × 10⁷ S⁻¹, and 3.22 × 10⁷ S⁻¹, respectively. It was revealed that BaTiO<inf>3</inf> filled in PA films reduced both Et value and υ.

Thermally stimulated current of polyaniline thin films

TSDC of a polyaniline thin film was measured with an electrode system (mica/ITO/EB film/ITO/mica). The comparative study of TSC and TSDC spectra revealed that both spectra contained two component current curves and the cause of the currents were different, though detailed mechanism of the current generation is still not clear.