Synthesis and laser processing of ZnO nanocrystalline thin films (original) (raw)
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Optical Properties of Annealed ZnO Thin Films Fabricated by Pulsed Laser Deposition
Silicon, 2015
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Enhancement of exciton emission from ZnO nanocrystalline films by pulsed laser annealing
Applied Surface Science, 2004
Pulsed ArF laser annealing in air and in hydrogen atmosphere improves the optical properties of ZnO nanostructured films. Independently on the ambient atmosphere, laser annealing produces two major effects on the photoluminescence (PL) spectra: first, the efficiency of the exciton PL increases due to decrease of the number of non-radiative recombination centers; second, the intensity of the defect-related orange band decreases because of the removing of excessive oxygen trapped into the films during deposition. However, annealing in the ambient air also increases the intensity of the green band related to oxygen vacancies. We show that the combination of laser annealing and passivation of oxygen vacancies by hydrogen results in films free of defect-related emission and keeps intact their nanostructural character.
Photoluminescence studies of ZnO thin films prepared using a laser-assisted sol-gel method
Journal of the Korean Physical Society, 2012
ZnO thin films were grown on Si(100) substrates by using a laser-assisted sol-gel method involving irradiation from a 325-nm He-Cd laser. In contrast to conventionally-synthesized sol-gel ZnO thin films, the surfaces of those grown using the laser-assisted sol-gel method were much smoother. The optical properties of the ZnO thin films were investigated using temperature-dependent photoluminescence (PL). In the room-temperature PL spectra, the intensity of the blue-green emission was dramatically decreased by laser irradiation during the stages of deposition and post-heat treatment. Moreover, the full width at half maximum of the near-band-edge emission peaks was decreased by the laser irradiation. The activation energy of the laser-assisted sol-gel ZnO thin films was determined to be ∼99 meV, and the values of the fitting parameters α and β for Varshni's empirical equation were 4 × 10 −3 eV/K and 4.9 × 10 3 K, respectively. Another fitting based on the thermal broadening effect of the excitonic emission peak revealed a decreased exciton-phonon interaction in the laser-assisted ZnO thin films.
Bulletin of the American Physical Society, 2009
College-ZnO thin films were grown by pulsed laser deposition using a Zn target in different atmospheres. The samples were characterized by SEM, XRD, EDX, and temperature dependent photoluminescence (PL) measurements. The growth conditions were varied sequentially from a pure oxygen to a pure nitrogen atmosphere, and the resulting changes of the material properties were investigated. The presence of nitrogen during growth was found to have a strong impact on the materials. Samples grown with higher nitrogen concentrations showed weak PL characteristics at room temperature as well as a small temperature dependence of the near band edge emission. At temperatures below 40 K, a sharp and pronounced emission peak was present at 3.362 eV. In an attempt to understand the PL characteristics, the samples were annealed in both pure oxygen and pure nitrogen environments at 600˚C. The samples grown with large nitrogen ratios exhibited a strong dependence on the annealing atmosphere; those annealed in nitrogen showed a strong increase in emissions in the 3.362 eV range compared to the same samples annealed in oxygen. In addition, the defect emissions of the samples were strongly affected by the presence of nitrogen during annealing. The possible role of nitrogen in ZnO growth and annealing is discussed.
Investigation on the origin of green luminescence from laser-ablated ZnO thin film
Thin Solid Films, 2003
ZnO thin films were grown at various ambient pressures by pulsed laser deposition. After depositions, ZnO thin films were annealed at 1 atm of O and forming gas (N :H s95:5), respectively. ZnO thin films were post-annealed in forming gas to 2 2 2 investigate the relationship between the oxygen vacancies and the photoluminescence (PL), since hydrogen gas could desorb the oxygen from the surface and the grain boundary of the film. From the X-ray diffraction (XRD) pattern exhibiting only the (0 0 2) XRD peak of ZnO, all films were found to be c-axis-oriented. The results of PL spectroscopy and Hall measurement could suggest that the origin of the green luminescence of ZnO thin film comes mainly from the defect centers caused by the oxygen vacancies.
Characterization on pulsed laser deposited nanocrystalline ZnO thin films
Vacuum, 2010
Nanocrystalline zinc oxide thin films were deposited on glass and silicon substrates by using pulsed laser deposition at different laser energy densities (1.5, 2, and 3 J/cm 2 ). The film thickness, surface roughness, composition, optical and structural properties of the deposited films were studied using an a-step surface profilometer, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), optical transmittance, and X-ray diffraction (XRD), respectively. The film thickness was calculated as 244 nm. AFM analysis shows that the root-mean-square roughness increases with increasing laser energy density. XPS analysis shows that the interaction of zinc with oxygen atoms is greatly increased at high laser energy density. In the optical transmittance spectra, a shift of the absorption edge towards higher wavelength region confirms that the optical band gap increases with an increase in laser energy density. The particle size of the deposited films was measured by XRD, it is found to be in the range from 7.87 to 11.81 nm. It reveals that the particle size increases with an increase in laser energy density.
Structural and morphological properties of thin ZnO films grown by pulsed laser deposition
Applied Surface Science, 2008
Tungsten-doped zinc oxide thin films were prepared by ablating a target containing 1 wt% WO 3 with XeCl excimer laser (λ=3O8 nm). The films were grown onto different glass substrate at a repetition rate of 10Hz, pulse energy of 100 mJ and irradiation time of 20 min. The structural and optical properties of the films are found to be strongly dependent on the nature of the substrate. The X-ray Diffraction (XRD) results show that all the films are preferentially C-axis oriented. The room temperature photoluminescence (PL) spectrum shows a dominant nearband-edge emission peak for the film deposited on borosilicate and GGG substrate. The average transmittance was found to be in the range of 84-90%. The absorption coefficient exhibits a direct bandgap feature with some band tailing effects.
2010
Ternary ZnCdO thin films oriented along c-axis have been successfully deposited on p-Si (1 0 0) substrates using sol-gel spin coating route. To optimize most suitable annealing temperature for the Zn 1−x Cd x O thin films; these films with selected cadmium content x = 0.10 were treated at annealing temperatures from 300 • C up to 800 • C in oxygen ambient after deposition. The structural and optical properties of deposited thin films have been characterized by X-ray diffraction, energy dispersive spectroscopy, atomic force microscopy, UV-Vis spectroscopy, and photoluminescence spectra. The results show that the obtained films possess high crystallinity with wurtzite structure. The crystallite size, lattice parameters, lattice strain and stress in the deposited films are determined from X-ray diffraction analysis. The band gap energy increased as a function of annealing temperatures as observed from optical reflectance spectra of samples. The presence of Cd in the deposited films is confirmed by energy dispersive spectrum and it is observed that Cd re-evaporate from the lattice with annealing. The photoluminescence measurements as performed at room temperature did not exhibit any luminescence related to oxygen vacancies defects for lower annealing temperatures, as normally displayed by ZnO films. The green yellow luminescence associated to these defects was observed at higher annealing temperatures (≥700 • C).
Synthesis and characterization of ZnO thin films for UV laser
Applied Surface Science, 2001
We report on deposition of zinc oxide thin ®lms on glass substrate at room temperature in ambient oxygen pressure ranging from 10 mTorr to 1 Torr by pulsed laser deposition. As grown polycrystalline thin ®lms were optically pumped to investigate the dependence of laser action and photoluminescence (PL) on stoichiometry and microstrucure of the ®lms. The intensity of the laser emission increases with thickness of the ®lm and depends on the size of nano-crystallites. Films deposited at pressures lower than 300 mTorr showed better morphology, stoichiometry and adhesion quality. X-ray diffraction, atomic force microscopy, Rutherford back scattering and PL techniques were used to characterize as grown ®lms. #
Journal of Physics D: Applied Physics, 2013
An investigation into the modification of low temperature deposited ZnO thin films by different annealing processes has been undertaken using laser, thermal and rapid thermal annealing of 60nm ZnO films deposited by Hi-Target-Utilization-Sputtering. Single pulse laser annealing using a KrF excimer laser (A = 248nm) over a range of fluences up to 315 mJ/cm 2 demonstrates controlled indepth modification of internal film microstructure and luminescence properties without the film degradation produced by high temperature thermal and RTA processes. Photoluminescence properties show that the ratio of defect related deep level emission (DLE, 450nm-750nm, 2.76eV-1.65eV) to excitonic near band-edge emission (NBE at 381nm, 3.26eV) is directly correlated to processing parameters. Thermal and rapid thermal processing results in the evolution of a strong visible orange/red DLE photoluminescence (with peaks at 590nm, 2.10eV and 670nm, 1.85eV) dominated by defects related to excess oxygen. At higher temperatures, the appearance of a green/yellow emission (530nm, 2.34eV) indicates a transition of the dominant radiative transfer mechanism. In contrast, laser processing removes defect related DLE and produces films with intense NBE luminescence, correlated to the observed formation of large grains (25-40nm).