Field-effect measurements in disordered As30Te48Si12Ge10and As2Te3

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Abstract
Field-effect data are presented for radio-frequency sputtered films of disordered As30Te48Si12Ge10 and As2Te3. The temperature dependence of the measurements is employed in order to determine the energy of the localized states controlling the field-effect response. By this means, it is established that these centres lie approximately 0·13 eV below the bulk Fermi level, and not at the Fermi level as has been assumed in previous analyses of the field effect is disordered chalcogenides. The experimental characteristics are discussed in terms of a variety of possible surface and bulk conditions, and it is shown that the data for both materials imply a higher density of localized states in the region within about 50 Å from the surface than that previously determined for the bulk. However, the available information does not allow a unique determination of the variation of localized-state distribution with position in the film. The experimental data and analytical conclusions are discussed in terms of current models for carrier transport in disordered semiconductors.