Yoshimi Kamitani

Analyses of Thermally Stimulated Current Curves with No Peaks

A theory that enables one to accurately estimate three parameters, namely, an energetic depth of carrier trap site Et, an escape frequency factor ν and a charge carrier density nt, from thermally stimulated current (TSC) curves with no peaks is proposed. Generally, these three parameters could not be evaluated from any TSC datum without peak coordinates. Such TSC data are usually measured experimentally in order to separate signals from each other in various composite cases. Our proposed theory makes it possible to evaluate several sets of three parameters. The proposal is a method to compensate the charges lost in experiments. Three types of charge compensation processes are reported in detail. The accuracy of evaluation of each of the three parameters is very good and the Et values of three significant figures could be obtained by numerical analyses.

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.

Behavior of the discrete energy states

A study comparing composite thermally stimulated current (TSC) curves that usually are measured by the single heating method, and partial curves from repeated heating and cooling processes, is reported. For this purpose, both the auto-separation (As) and reconstruction (Re) methods are necessary. The former enables us to separate accurately composite curves obtained by one heating process into several TSC curves with a single relaxation process. The latter enables us to reconstruct TSC curves from partial curves obtained by repeated heating and cooling, even if they had no observed peak. Both methods apply a theory, using the fundamental element that was defined originally to be the smallest quantity and a coordinate determined arbitrarily on the measured TSC curves. The current type of charge compensation equation that makes accurate RC procedure possible was first proposed. From detailed analysis, it was confirmed that an electron trap and a hole trap are produced simultaneously in a naphthacene doped anthracene single crystal. Analysis suggests that repeated heating and cooling influences both trap sites and that the indirect transport mechanisms via discrete state-to-state charge transfer processes is not negligible.

Proposal of reconstructing method of partial TSC curves to some full curves for accurate evaluation

An original theory that three parameters, the energy depths of carrier traps E/sub t/, the escape frequency factor /spl nu/ and the density of carrier trap site n, can be theoretically evaluated with high accuracy from partial TSC curves is proposed. How the standard can be constructed has been a most important resultant point.

Behavior of the discrete states observed through detailed analyses of TSC curves

In order to make the electronic transport mechanism in organic substances clear in detail, the thermally stimulated current (TSC) method is very effective. From the TSC method, three parameters such as an energy depth E/sub t/ [eV] of the carrier trap site, a preexponential parameter (or an escape frequency factor) /spl nu/ [s/sup -1/] and a charge carrier density n/sub t/ [m/sup -3/] relating to the phenomena, can be estimated. We have completed some theories that enable us to analyze in detail TSC data obtained experimentally. One of them, the asymptotic estimation method (AEM) originally proposed by us, enables us to evaluate these three parameters accurately. And this has been expanded extensively to estimate 3N parameters, through an exact auto-separation (AS) method of various composite TSC curves and through the reconstruction (RC) method of TSC curves with no peak obtained by partially repeated heating cooling procedures. Where N is the number of the single TSC curve of the first-order included in the objects. The fine advantages are that these expanded theories have higher accuracy than 4 significant figures. Then, detail analyses of discrete states became possible by using both methods.

Discrete states in anthracene with and without impurities

It has been confirmed from TSC experiments and analyses that there were some groups of discrete state in anthracene single crystals with and without impurities and two kinds of state to state transition of carriers played important roles in their electrical conduction.

Electric behaviour of ZnO varistor studied from TSC measurement

In this paper, the results of the ZnO varistor voltage-current characteristics and the thermally stimulated current (TSC) components separated in the temperature range from 50 to 340 K are reported. Additionally, some experimental results before and after applying high-voltage impulse (10 kV) as a false load are reported and discussed. From the experiments on the TSC of ZnO varistor, the following results were obtained: (1) some TSC curves (four or six) of the first-order that correspond to the discrete state individually in the grain boundary can be separated in the temperature range from 50 to 340 K. (2) The dominant TSC peak appeared around room temperature. The trap depth, Et, of this peak depends on the poling field Ep. As Ep increases, Et increased from ca. 0.31 to 0.38 eV. (3) The /spl nu/ value for the dominant TSC peak varied from ca. 10/sup 2/ to 10/sup 3/ 1/s. (4) From this detailed study on the /spl nu/ value of traps, it is understood that the varistor effect depends on the /spl nu/ value of the dominant TSC peak.

Discrete states in organic substances

A new theory of the thermally stimulated current utilizing the fundamental element and its application is reported. Without this original theory, discrete states especially in organic substances and their interesting relation to the conduction mechanism can never be discussed. The theoretical bases making these detailed discussion possible are reported in this conference.