Etude structurale et optique de films minces ZnO élaborés par voie physique et/ou chimique

Abstract

In the present work, we have studied essentially the structural and optical properties of ZnO thin films elaborated using the physical technique s of the pulsed laser ablation (PLD) and the chemical method of the ultrasonic spray pyrolysis. We have prepared undoped (ZnO) and cobalt-doped zinc oxide (CZO) thin films (Co: 3,5 at.%) by means of the PLD method. Synthesized films have been deposited on glass and silicon substrates heated at 450°C. The used source was a KrF eximer laser (248 nm, 25 ns, 2 J ⁄cm2). Different experimental techniques have been carried out to analyze the fabricated films: the X-ray diffraction (XRD), atomic force microscopy (AFM), Rutherford Backscattering spectrometry (RBS), UV-visible spectrophotometry, M-lines spectroscopy and Hall effect. While the ZnO films obtained by the ultrasonic spray technique have been deposited with different deposition times (10, 20, 30 min) on a glass substrate heated at 410 °C, and then they have characterized by XRD, AFM, UV-visible, M-lines and hall effect techniques. The carried out study shows that all the prepared zinc oxide films have a hexagonal wurtzite-type structure and a preferentially oriented along the direction (002) confused with the c-axis perpendicular to the surface of the substrates. The grain sizes deducted from the XRD measurements vary between 24 and 40 nm. The optical coupling analysis realized by M-lines show that the ZnO films are monomode (for both TE and TM polarizations). However, the undoped ZnO film obtained by PLD is found to be two guiding modes for TM. The films obtained have an optical transmission of 70 to 90% in the visible region of the spectrum and an optical band gap varying from 3.18 to 3.37 eV. The electrical conductivity and the concentration of carriers, deduced from Hall effect measurements, are relatively low namely for the films prepared by spray pyrolysis technique.