Analysis of the thermally stimulated capacitor-discharge method for characterizing localized states in amorphous semiconductors

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Abstract
A detailed analysis of the method of thermally stimulated capacitor discharge (TSCD) is presented. Distinction is made between the dielectric relaxation currents and the trap-limited currents. The position, shape, and number of the depolarization peaks caused by the dielectric relaxation currents are shown to depend (i) on the conductivity of the sample as a function of temperature and electric field and (ii) on the geometry of the sample. It is pointed out that the behavior of the dielectric-relaxation-current peaks is quite similar to the trap-limited-current peaks, and an analysis of the peaks may lead to false conclusions, if done without distinguishing them from one another. We assert that no new information about the trap parameters can be obtained from TSCD, unless the structure of the polarization and depolarization curves are different. No such difference was found in the chalcogenide glass studied by us, and the observed TSCD could be explained in terms of dielectric relaxation currents only. We also point out that a low drift mobility, a short screening length, and possibly a large density of localized states near the Fermi level, make the observation of trap-limited TSCD in multicomponent chalcogenides unlikely.