Proposal of the reconstruction method of composite TSC curves and a study of the electrical conduction mechanisms is organic substances

摘要

In order to make the charge transport mechanism in organic substances clear in details, the thermally stimulated current (TSC) method is very effective. From the TSC method, three parameters such as the energy depth of carrier trap site E{sub}t (eV), a pre - exponential parameter (or an escape frequency factor) v (s{sup}(-1)) and a charge carrier density n{sub}t (m{sup}(-3)) of discrete states relating to the charge transport mechanism can be estimated. However, accurate values of these parameters could not be generally estimated for various types of composite curves obtained experimentally. In such cases, some partial TSC curves have been generally observed through repeated heating and cooling processes to separate composite causes experimentally. In such cases, it was not unusual that the experimental data with no peak were obtained, and the three parameters for these data could not be estimated until now. In this paper, I have proposed the reconstruction (RC) method for the first time. The RC method enables us to estimate 3N parameters accurately through the accurate reconstruction procedures from partial curves with no peak to some single TSC curves, where N is the number of the single TSC curves concealed in data. Also I have presented some analyzed results. The proposed RC method and the auto - separation (AS) method that enables us to accurately separate composite curves obtained by one heating process into some TSC curves with single relaxation processes were applied to data obtained experimentally in naphthacene - doped anthracene single crystals as a representative of organic semiconductors. E{sub}t and v values estimated from the AS method are slightly larger than that from the RC method. This result suggests that the indirect transport mechanisms via discrete state - to - state charge transfer processes is not negligible.