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Effect of the oxygen on the optical, structural and electrical properties of ZnF2 thin films prepared by DC reactive sputtering

Mohamed Kechouane 1Abderrahmane Boughelout 1Kamel Taibi 2Menouar Siad 3Hamid Menari 4

1. Laboratoire "Couches Minces et Semiconducteurs" - USTHB - Faculté de Physique -, BP 32 El-Alia - Bab-Ezzouar, Alger 16111, Algeria
2. Laboratoire des Sciences et Génies des Matériaux, Faculté de Génie Mécanique, USTHB, BP 32, El-Alia, Bab Ezzouar, Alger 16111, Algeria
3. Centre de Recherche Nucléaire d'Alger (CRNA), 02 Boulevard Frantz Fanon, Alger 16000, Algeria
4. Unité de Développement de la Technologie du Silicium (UDTS), 02 Boulevard Frantz Fanon, BP 140, Alger-7merveilles, Alger 16100, Algeria


Zinc fluoride (ZnF2) is an insulating wide band gap crystal has been recently demonstrated that this material is attractive for applications as efficient light emitter in the UV.

Crystalline ZnF2 films of a rutile-type structure were obtained on corning-glass and silicon substrates kept at 100 and 300°C. A film growth along  [110] direction was found.  An amorphous ZnF2 film was obtained when the substrate was kept at 100°C.

The ZnF2 thin films were elaborated on silicon and corning glass substrates by using a reactive sputtering with an argon/oxygen/fluorine mixture from a metallic Zn target at 100°C and at constant working total pressure of 100 Pa. The ZnF2 thin films were investigated by optical transmission, X-ray diffraction (XRD), scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS) and electrical conductivity measurements. The transmittance measurements have shown that all films exhibit high transmittance in the 400–2500 nm range. The averaged transmittance of the ZnF2 film increased from 80 to 94% upon vacuum-annealing at 300°C for 1 hour (Fig.1). The crystalline structure of ZnF2 thin films indexed by XRD reveals tetragonal lattice with cell parameters a =b= 4.7034 Å and c = 3.1335 (Fig.2). The RBS measurements reveal that ZnF2 thin films are almost stoichiometric, with an atomic composition close to Zn(34%) F(66%). The surfaces morphology of ZnF2 thin films deposited at 100°C, from the scanning electron microscopy images, shows significant changes due to the oxygen partial pressure used during the film deposition. A porous surface consisting of circular craters, with an average diameter ranging between 0.2 and 20nm is revealed. The dark conductivity sd versus temperature, in the Arrhenius plot, from a ZnF2 thin films deposited at 100°C and after vacuum-annealing at 300°C for one hour clearly evidenced a very large increase in electrical conductivity, from 10-10 to 10 (Fig.3).


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Presentation: Oral at E-MRS Fall Meeting 2009, Symposium C, by Mohamed Kechouane
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-11 00:23
Revised:   2009-06-07 00:48