Influence of Doping and Annealing on Structural, Optical and Electrical properties Amorphous ZnOThin Films Prepared by PLD

Abstract

In this work,ZnO thin films pure and doped with oxides (GaO ) were deposited using pulsed laser deposition (PLD) technique using a double frequency Q-switching Nd:YAG laser beam (λ=532) nm , repetition rate (6) Hz and the pulse duration (10 ns). After the end of wet mixing and drying process, the mixtures were pressed to form pellets (1.3cm) diameter by using (3ton) pressure. and sintered at (1373K) for (5hr). The product was investiged using XRD. The data of x-ray diffraction shows Polycrystalline structure, and exhibited hexagonal structure .The film of thickness equal to 300 nmwith rate of deposition equal to 0.5 nm/sec.ZnO thin films pure and doped with (0.02,0.06 and 0.1)wt٪of (GaO) have been deposited on glass substrates at room temperature.These films have been annealed at different temperatures (373,473 and 673)K .The structural characteristics of the films prepared on glass substrates show that all the films have amorphous structure at room temperature and 373K but when the sample are annealing at (473and673)K the XRD detected a hexagonal phase of ZnO the same occurs with doping .. But annealing up to (673K) the XRD detected a hexagonal phase of ZnO the same occurs with doping samples. The surface morphology of the deposit materials were studied using atomic force microscope (AFM), The grain size of the particles observed at the surface depended on the annealing temperature. UV-VIS transmittance measurements showed that the films are highly transparent in the visible wavelength region for samples annealing up to 473K on glass, while at annealing temperature of 673K the absorption edge of ZnO doped with (GaO) was shifted to near-infrared region. The optical gap of the films was calculated from the curve of absorption coefficient (αhע) 2 vs. hע and was found to be 3.8eV at room temperature, and this value decreases from (3.8-3.58eV) with increasing of annealing temperature up to (473-673)K, and increases with different elements oxides dopants. λ cutoff have been calculated for ZnO and showed an increase with increasing annealing temperature and shift to longer wavelength. while with doping the λ cutoff shift to shorter wavelength . The Photoluminescence (PL) results indicates that the thin films fabricated at glass substrate shows the strong peaks at (640nm) for ZnO films grown at room temperature , but doping ZnOwith Ga showed a band emission in yellow-green of spectra(380-450)nm.