S. Alaya

Electrical and optical properties of aluminum-doped zinc oxide sputtered from an aerogel nanopowder target

ZnO:Al thin films doped with different aluminum concentrations were deposited onto glass substrates by rf-magnetron sputtering at ambient temperature using, for the first time, nanocrystalline powder synthesized by the sol–gel method. The aluminum doping concentration was varied from 2.0 to 4.5xa0at.%. All the films exhibited an intensive (002) XRD peak, indicating that they have c-axis-preferred orientation. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to study the morphology of the films. They have a typical columnar structure and a very smooth surface. The optical transmittance spectra showed a good transmittance higher than 90% within the visible region. The best conductors, with an optical band gap of 3.46xa0eV and a minimum resistivity of 5.4 × 10−4xa0Ωxa0cm, were obtained for ZnO:Al films containing 3.0xa0at.% of aluminum. Due to their good optical and electrical properties, ZnO:Al films are promising candidates for use as transparent electrodes in solar cells.

Ab initio study of heterojunction discontinuities in the ZnO/Cu2O system

Solar cells based on transparent conductive oxides such as ZnO/Cu2O constitute a very advanced way to build high-performance cells. In this work, we are interested in the characterization of the interface through nanoscale modeling based on ab initio approaches (density functional theory, local density approximation, and pseudopotential). This work aims to build a supercell containing a heterojunction ZnO/Cu2O and study the structural properties and the discontinuity of the valence band (band offset) from a semiconducting to another phase. We build a zinc oxide in the wurtzite structure along [0001] on which we place the copper oxide in the hexagonal (CdI2-type) structure. We choose the method of Van de Walle and Martin to calculate the energy offset. This approach fits well the density functional theory. Our calculation of the band offset gives a value that corresponds to other experimental and theoretical values.