Intentionally disordered superlattices with high dc conductance

We study disordered quantum-well-based semiconductor superlattices where the disorder is intentional and short-range correlated. Such systems consist of quantum-wells of two different thicknesses randomly distributed along the growth direction, with the additional constraint that wells of one kind always appears in pairs. Imperfections due to interface roughness are considered by allowing the quantum-well thicknesses to fluctuate around their {\em ideal} values. As particular examples, we consider wide-gap (GaAs-Ga$_{1-x}$Al$_{x}$As) and narrow-gap (InAs-GaSb) superlattices. We show the existence of a band of extended states in perfect correlated disordered superlattices, giving rise to a strong enhancement of their finite-temperature dc conductance as compared to usual random ones whenever the Fermi level matches this band. This feature is seen to survive even if interface roughness is taken into account. Our predictions can be used to demonstrate experimentally that structural correlations inhibit the localization effects of disorder, even in the presence of imperfections. This effect might be the basis of new, filter-like or other specific-purpose electronic devices.Comment: REVTeX 3.0, 20 pages, 7 uuencoded compressed PostScript figures as a separate file. Submitted to IEEE J Quantum Elec

EVALUATION OF RURAL DEVELOPMENT PROGRAMMES FAILURES WITHIN THE 2007-13 REGIONAL POLICY FRAME

New 2007-13 planning framework of the EU keeps using economic criteria (GDP) to identify those regions requiring priority attention (convergence objective). Although these criteria are useful for the overall Regional Policy, nevertheless it might result some planning failures of the strategies of rural development. This work focuses in evaluating possible failures of the Rural Development Programmes. For this purpose, a wide range of member Estates and Regions has been selected and two analysis have been applied: first, the coherence analysis (in relation to the economic, social and environmental situation of territories); and second, the conflict (among the rural territories development objectives) analysis. As result of this evaluation, a typology of the analysed Rural Development Programmes will be shown, which identifies different cases of failures. This work concludes that the use of methodological criteria in Regional Policy complementing to the Efficiency criteria might improve the territorial cohesion process and reduce some of the analysed failures in rural areas.Rural Development Programmes, Regional Policy, European Union, Community/Rural/Urban Development,