Transport phenomena of Cu-S-Te chalcogenide nanocomposites: frequency response and AC conductivity.

In this work, the development and electrical characterization of several chalcogenide nanocomposites have been reported. X-ray diffraction (XRD) has been used to reveal their microstructures. Mott's variable range hopping model has been used to interpret the DC conductivity data of the nanocomposites at lower temperatures. The DC conductivity data at higher temperatures has been explained well using Greave's model. To explain the AC conductivity data, the Meyer-Neldel (MN) conduction rule has been employed. The AC conductivity spectra at different temperatures have been analyzed using Almond-West formalism. Different conduction models, namely, correlated barrier hopping (CBH) and modified non-overlapping small polaron tunneling (NSPT), have been used to interpret the conduction mechanism of the nanocomposites. Scaling of the AC conductivity spectra reveals that the electrical relaxation process is independent of temperature, but depends on the nanocomposite composition. The conductivity mechanism is explained using a schematic structural model.

Evolution of nc-Si network and the control of its growth by He/H2 plasma assistance in SiH4 at PECVD.

The evolution of nc-Si network and the control of its growth within quantum dot structures have been systematically studied by He/H2 plasma assistance in SiH4. Using the beneficial aspects of He* and He+ in the purely helium-diluted silane plasma and optimizing the process parameters, nanocrystalline silicon films are produced at high growth rates. The nc-Si:H network of increasing electrical conductivity and improved crystallinity are obtained with simultaneously increasing deposition rates, which deserve extensive technological impact. Starting with a mixed phase heterogeneous matrix in the neighborhood of amorphous-to-crystalline transition zone, the effect of H2 in the reconstruction of the network, triggering nanocrystallization, was studied using (SiH4+He+H2)-plasma. A radical change in the materials properties has been accomplished by the inclusion of a small amount of H2 as the component diluent. Sharp rise in the overall crystallinity, well aligned crystallographic lattice distribution, gross removal of porosity and sharp elevation of electrical conductivity by several orders of magnitude are the consequences which are accompanied by a relatively insignificant lowering in the growth rate because of required H2-dilution in trivial amounts. Partial hydrogenation to the mostly He diluted SiH4 plasma has been identified as the favored route for attaining spontaneous nanocrystallization in the Si-network and its confinement of structures within quantum dot dimensions.