Etude de phases delafossite CuFe1-xCrxO2 : vers de nouveaux TCO de type p

Ces travaux ont pour objectif d'élaborer sous forme de couches minces des phases delafossite CuFe1-xCrxO2:Mg par pulvérisation cathodique radiofréquence, en vue de leur utilisation potentielle en tant que conducteurs transparents. Différentes poudres de composition CuFe1-xCrxO2 (0 = x = 1) ont été élaborées par réaction à l'état solide. Ces oxydes cristallisent avec la structure delafossite et une solution solide complète a été obtenue. L'étude thermostructurale de ces composés nous a permis de définir leur domaine de stabilité sous atmosphère oxydante et réductrice. Des caractérisations physico-chimiques ont également été effectuées sur ces matériaux. Nous avons ainsi montré que le domaine de stabilité des phases CuFe1-xCrxO2 augmente avec la quantité de chrome et que les composés riches en chrome sont les plus conducteurs et les moins absorbants. Au vue de ces résultats, des films minces de delafossite de composition CuFeO2:Mg et CuCrO2:Mg ont été obtenus par pulvérisation cathodique RF à température ambiante à partir des cibles céramiques. Après recuit sous vide à 450°C, les propriétés optoélectroniques des dépôts de CuFeO2:Mg se sont avérées limitées pour une utilisation en tant que TCO de type p dans le domaine du visible ; toutefois ces composés restent prometteurs pour des applications dans l'infra-rouge ou comme matériaux absorbeurs dans le visible. Les couches minces de CuCrO2:Mg présentent, après recuit sous vide à 450°C, une conductivité de type p de l'ordre de 0,1 S.cm-1 et un gap optique de 3,13 eV. Ces valeurs peuvent être augmentées par des recuits à des températures supérieures à 450°C.This work concerns the development of CuFe1-xCrxO2:Mg delafossite oxide thin films deposited by RF-magnetron sputtering for the potential transparent conductor applications. Various CuFe1-xCrxO2 (0 = x = 1) powders were synthesized by a standard solid-state reaction. These oxides crystallize with the delafossite structure and a complete solid solution was obtained. Thermo-structural study has revealed the stability range of CuFe1-xCrxO2 compounds under oxidizing and reducing atmosphere. Their physical properties were also characterized. Thus, we showed that the stability range increases with the chromium quantity and chromium-rich delafossites are the most conductive and the least absorbent. Then, CuFeO2:Mg and CuCrO2:Mg delafossite thin films were prepared at room temperature by RF-magnetron sputtering from ceramic targets. After annealing under vacuum at 450°C, CuFeO2:Mg thin films have too low optoelectronic properties for p-type TCO application in the visible range; however these compounds are promising for infra-red TCO applications and/or absorber for photovoltaic application. After annealing under vacuum at 450°C, the p-type conductivity and the bandgap of CuCrO2:Mg thin films are about 0,1 S.cm-1 and 3,13 eV respectively. These values can be increased by annealing at higher temperature than 450°C

p-Type conducting transparent characteristics of delafossite Mg-doped CuCrO2thin films prepared by RF-sputtering

The growth of technologically relevant compounds, Mg-doped CuCrO2 delafossite thin films, on a quartz substrate by radio-frequency sputtering is reported in this work. The deposition, performed at room temperature, leads to a nanocrystalline phase with extremely low roughness and high density. Delafossite characteristic diffraction peaks were obtained as a function of the thermal treatment under primary vacuum. The electrical conductivity was optimized until 1.6 S cm−1 with an optical transmittance of 63% in the visible range by a 600 °C annealing treatment under primary vacuum applied for 4 h. The transport properties were analyzed by Seebeck and Hall measurement, integrated spectrophotometry and optical simulation. These measurements highlighted degenerated semiconductor behavior using a hopping mechanism with a high hole concentration (1021 cm−3) and a low mobility (0.2 cm2 V−1 s−1). The direct optical bandgap of 3.3 eV has been measured according to Tauc's relationship. A refractive index of 2.3 at a wavelength of 1100 nm has been determined by spectroscopic ellipsometry and confirmed by two independent modellings of the optical transmittance and reflectance spectra. All these p-type TCO optoelectronic characteristics have led to the highest Haacke's figure of merit (1.5 × 10−7 Ω−1) reported so far for such delafossite material

Structured ZnO-based contacts deposited by non-reactive rf magnetron sputtering on ultra-thin SiO2/Si through a stencil mask

In this paper, we study the localized deposition of ZnO micro and nanostructures deposited by non-reactive rf-magnetron sputtering through a stencil mask on ultra-thin (10 nm) SiO2 layers containing a single plane of silicon nanocrystals (NCs), synthetized by ultra-low energy ion implantation followed by thermal annealing. The localized ZnO-deposited areas are reproducing the exact stencil mask patterns. A resistivity of around 5×10−3 Ω cm is measured on ZnO layer. The as-deposited ZnO material is 97% transparent above the wavelength at 400 nm. ZnO nanostructures can thus be used as transparent electrodes for Si NCs embedded in the gate-oxide of MOS devices

Étude de phases delafossite CuFe1-xCrxO2 (vers de nouveaux TCO de type p)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF