Photoluminescence Properties of ZnO Thin Film Prepared by Sol-Gel Route (original) (raw)
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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.
UV Photoluminescence of ZnO Nanostructures Based Thin films synthesized by Sol Gel method
2016
During past few decades, Zinc oxide thin films have gained much interest of the researchers, due to its applications in the wide range of fields of optoelectronic devices, photovoltaic, semiconductor lasers and modern LED’s. Selection of proper growth technique for ZnO nanostructures governs several structural and electrical parameters. ZnO shows n-type behavior naturally, donor defects are responsible for emission of UV spectra. ZnO is a wide band gap material with excellent physical properties, good heat conductor, transparent, electron mobility is high and it is non-toxic. Nanostructures based ZnO thin films are prepared using sol-gel and spin coating method. XRD results reveals hexagonal structure of ZnO. Photoluminescence in the utra-violet range maybe due to near-band-edge (NBE) transitions. Ultra violet emissions are observed and can be induced by the band edge recombination of ZnO. This ultra-violet luminescence has origin in free exciton emission. UV luminescence is due to ...
Applied Physics Letters, 2005
Abstract Temperature-dependent photoluminescence (PL) of nanocrystalline ZnO thin films grown on Si (100) substrates using a sol–gel method has been investigated. From the PL spectra measured in 83–293 K, the excitonic emissions and their multiple-phonon replicas have been observed in ultraviolet region, and their origins have been identified. Moreover, it has been found that the temperature dependence of the free exciton peak position can be described by standard expression, and the thermal activation energy extracted from the ...
Temperature-dependent luminescence dynamics for ZnO thin films
Optical and Quantum Electronics, 2013
The paper presents the photoluminescence investigation of zinc oxide thin films. A high quality ZnO films fabricated by dip-coating (sol-gel) method were grown on quartz wafers. The films with different thickness (number of layers) were annealed at different temperatures after the preparation process. It was found that high quality, transparent ZnO thin films could be produced on quartz substrates at relatively low annealing temperature (450-550 • C). The dependence of the ZnO thin film quality was studied by X-ray diffraction and atomic force microscopy techniques. Optical properties were investigated by classic and time-resolved photoluminescence (TRPL) measurements. Photoluminescence spectra allowed us to estimate energy of the free excitons, bond excitons and their longitudinal optical (LO) phonon replicas as a function of the annealing temperature. An innovative TRPL technique let us precisely measure the decay time of the free-and bond excitons' in the real time. TRPL measurements as a function of temperature reveal a biexponential decay behavior with typical free/bound exciton decay constants of 970/5310 ps for the as-grown sample and 1380/5980 ps after annealing process. Presented spectra confirm high structural and optical quality of investigated films. We proved that the thermal treatment improve both optical and structural quality and extend the photoluminescence's lifetimes. The obtained experimental results are important for identification of exciton's peaks and their LO phonon replicas for the investigated ZnO films.
Optical properties of ZnO thin films prepared by sol–gel process
Microelectronics Journal, 2009
The present study focused on ZnO thin films fabricated by sol-gel process and spin coated onto Si (1 0 0) and quartz substrates. ZnO thin films have a hexagonal wü rtzite structure with a grain diameter about 50 nm. Optical properties were determined by photoluminescence (PL) and absorption spectroscopy. The absorption spectrum is dominated by a sharp excitonic peak at room and low temperatures. At room temperature, two transitions were observed by PL. One near to the prohibited energy band in ultraviolet (UV) region and the other centered at 640 nm, characteristic of the electronic defects in the band-gap. The spectrum at 6 K is dominated by donor-bound exciton lines and donor-acceptor pair transition. LO-phonon replica and two-electron satellite transitions are also observed. These optical characteristics are a signature of high-quality thin films.
Localized excitons mediate defect emission in ZnO powders
Journal of Applied Physics, 2013
A series of continuous-wave spectroscopic measurements elucidates the mechanism responsible for the technologically important green emission from deep-level traps in ZnO:Zn powders. Analysis of low-temperature photoluminescence (PL) and PL excitation spectra for bound excitons compared to the temperature-dependent behavior of the green emission reveals a deep correlation between green PL and specific donor-bound excitons. Direct excitation of these bound excitons produces highly efficient green emission from near-surface defects. When normalized by the measured external quantum efficiency, the integrated PL for both excitonic and green emission features grows identically with excitation intensity, confirming the strong connection between green emission and excitons. The implications of these findings are used to circumscribe operational characteristics of doped ZnO-based white light phosphors whose quantum efficiency is almost twice as large when the bound excitons are directly excited. V C 2013 American Institute of Physics. [http://dx.
Study of the photoluminescence emission line at 3.33 eV in ZnO films
Journal of Applied Physics, 2012
We study properties of the line at 3.33 eV observed in photoluminescence (PL) emission spectra of various ZnO films prepared using pulsed laser deposition method. The influence of deposition parameters, such as oxygen pressure, laser fluence, post-annealing, and electric field exposure on intensity of this luminescence band has been investigated. The recombination characteristics are probed by temperature and excitation dependent PL spectroscopy. The obtained experimental data suggest that the 3.33 eV luminescence line in ZnO depends strongly on surface band bending and originates from recombination of bound excitons (BEs) complex located near the surface and grain boundaries. The anomalously small thermal activation energy of BE in comparison with the localization energy is explained by decreasing of the interface barrier. Possible nature of defects that bind free excitons and cause the 3.33 eV emission line in ZnO is proposed. V
Energy Shift of Native 2.45 eV Related Defects in Annealed ZnO Films
IOP Conference Series: Materials Science and Engineering, 2010
We study the influence of annealing temperature on the structural and optical properties of ZnO. Zinc oxide films were prepared by thermal oxidation of metallic Zn films. First, high quality (5N) Zn was evaporated onto sapphire substrate. Then zinc films were annealed in the oxygen atmosphere at several temperatures from 500 o C to 1100 o C. The surface was analyzed by Scanning Electron Microscopy (SEM) and structural properties were studied by XRD. Photoluminescence (PL) was measured from 350 nm to 800 nm, at two temperatures -80 K and 300 K. Ordinary PL spectra could be divided into two parts. One band observed at ~3.3 eV (UV PL) and second at 2.2 -2.5 (VIS PL as "visible") -the maximum energy depends on annealing temperature. The origin of UV PL is in recombination of free excitons and bound excitons to donors and acceptors [1]. However, for VIS PL exact mechanism of emission recombination is still not fully understood. The main discussion is related to the native defects such as zinc vacancies or oxygen vacancies or oxygen antisite [2] but impurities like Cu [3] and/or hydrogen donors [4] are also candidates. Sample annealing temperature influenced the peak position of VIS PL and intensity of both part of the PL spectrum
Bound excitons in ZnO: Structural defect complexes versus shallow impurity centers
Physical Review B, 2011
ZnO single crystals, epilayers, and nanostructures often exhibit a variety of narrow emission lines in the spectral range between 3.33 and 3.35 eV which are commonly attributed to deeply bound excitons (Y lines). In this work, we present a comprehensive study of the properties of the deeply bound excitons with particular focus on the Y 0 transition at 3.333 eV. The electronic and optical properties of these centers are compared to those of the shallow impurity related exciton binding centers (I lines). In contrast to the shallow donors in ZnO, the deeply bound exciton complexes exhibit a large discrepancy between the thermal activation energy and localization energy of the excitons and cannot be described by an effective mass approach. The different properties between the shallow and deeply bound excitons are also reflected by an exceptionally small coupling of the deep centers to the lattice phonons and a small splitting between their two electron satellite transitions. Based on a multitude of different experimental results including magnetophotoluminescence, magnetoabsorption, excitation spectroscopy (PLE), time resolved photoluminescence (TRPL), and uniaxial pressure measurements, a qualitative defect model is developed which explains all Y lines as radiative recombinations of excitons bound to extended structural defect complexes. These defect complexes introduce additional donor states in ZnO. Furthermore, the spatially localized character of the defect centers is visualized in contrast to the homogeneous distribution of shallow impurity centers by monochromatic cathodoluminescence imaging. A possible relation between the defect bound excitons and the green luminescence band in ZnO is discussed. The optical properties of the defect transitions are compared to similar luminescence lines related to defect and dislocation bound excitons in other II-VI and III-V semiconductors.
Luminescence properties of defects in ZnO
Physica B-condensed Matter, 2007
We briefly review the luminescence properties of defects in ZnO responsible for broad bands in the visible part of the photoluminescence (PL) spectrum. Bulk and thin-film ZnO samples produced by several companies and research groups were studied at different temperatures and excitation intensities. Steady-state and time-resolved PL was analyzed. We resolved and classified about 10 PL bands having maxima from 1.75 to 2.6 eV at 10 K. Types of transitions and possible assignments of the PL bands are briefly discussed. r