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The nature of the sulfur deficit in pyrite, as found before by chemical analysis and density measurements, has been investigated by powder x-ray diffraction (XRD). Structure-factor refinements showed that the sulfur population parameter deviates several percent from unity, although the cubic-unit-cell edge a only varies in the order of ${10}^{\mathrm{-}3}$ Å. To do these high-precision a measurements, a determination of the Cu K${\mathrm{\alpha }}_2$ wavelength is made. Vegard’s rule for sulfur-deficient pyrite is presented. The sulfur deficit is explained as a simple Schottky defect, whose vacancy-formation energy is about 0.3 eV. On the basis of ligand-field- and molecular-orbital-theory considerations, the band-structure model of pyrite is modified due to the presence of S vacancies. The most important electronic effect is the formation of defect states in the forbidden zone. This result will be discussed with respect to contradictory measurements concerning the electronic properties of pyrite.

We report on direct evidence of ultrafast carrier dynamics displaying features on the picosecond time scale in microcrystalline silicon $\mathrm{(\mu c-}\mathrm{Si:H}\mathrm{).}$ The dynamics of photogenerated carriers is studied by using above-band-gap optical excitation and probing the instantaneous carrier mobility and density with a THz pulse. Within the first picoseconds after excitation, the THz transmission transients show a fast initial decay of the photoinduced absorption followed by a slower decrease due to carrier recombination. We propose that the initial fast decay in the THz transients is due to carrier capture in the trapping states.

Thin polycrystalline films are often observed to develop a preferred orientation or texture that may have significant effects on film properties, especially in the case of anisotropic crystal structures. We report on a x-ray diffraction study of texture evolution in hexagonal ZnO:Al films, which were performed with a highly sensitive large-area detector enabling the investigation of films with thicknesses of some 10 nm only. In a set of magnetron-sputtered ZnO:Al films with thicknesses between 20 and 500 nm the resistivity was found to decrease with increasing thickness. A comprehensive texture analysis was performed within the framework of the series expansion method of the orientation distribution function (ODF). The investigations reveal a clear correlation between preferred grain orientation and electrical properties in ZnO:Al films. A general model is presented which relates the electronic mobility in polycrystalline films with the ODF by assuming the mobility to be composed of an intra-grain and an inter-grain fraction. It turns out that intra-grain anisotropy in ZnO:Al films cannot account for the observed variations in resistivity. Regarding the charge carrier scattering at grain boundaries the model relates the resistivity to the degree of grain alignment and makes use of the texture index $J.\mathrm{}$ On the basis of these assumptions it is shown that the resistivity scales with $1/J.$ The model also predicts the attainable minimum resistivity of thin ZnO:Al films with perfectly aligned crystallites which is in accordance with previously published results.