Improvement in the crystallinity of ZnO thin films by introduction of a buffer layer (original) (raw)
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Improvement of ZnO thin film properties by application of ZnO buffer layers
Journal of Crystal Growth, 2007
The effect of ZnO buffer layers prepared at different temperatures on the structural, optical and morphological properties of the ZnO main layer is reported. ZnO thin films (comprising a buffer and a main layer) were deposited on (0 0 0 1) c-sapphire substrates by PEMOCVD. Two-step growth regimes were applied to realize a homoepitaxial growth on ZnO buffers: low-temperature ZnO buffer layer deposited at T s ¼ 300 1C and the main layer at T s ¼ 500 1C; high-temperature ZnO buffer layer deposited at T s ¼ 500 1C and the main layer at T s ¼ 300 1C. For comparison, a sample grown at high-temperature T s ¼ 500 1C by one-step procedure was used. The lowtemperature buffer layer has shown the most beneficial effect on the structural and morphological properties, as expressed by the narrowing of the (0 0 2) diffraction peak (FWHM ¼ 0.071) and crystallite size enlargement. However, the surface roughness of this sample is higher then that of the sample grown by one-step procedure and this needs further considerations. The photoluminescence results seem to support a conclusion that the application of a low-temperature buffer layer among the studied temperature regimes is the most advantageous. r
Crystallinity Improvement of ZnO Thin Film on Different Buffer Layers Grown by MBE
Journal of Nanomaterials
The material and optical properties of ZnO thin film samples grown on different buffer layers on sapphire substrates through a two-step temperature variation growth by molecular beam epitaxy were investigated. The thin buffer layer between the ZnO layer and the sapphire substrate decreased the lattice mismatch to achieve higher quality ZnO thin film growth. A GaN buffer layer slightly increased the quality of the ZnO thin film, but the threading dislocations still stretched along the c -axis of the GaN layer. The use of MgO as the buffer layer decreased the surface roughness of the ZnO thin film by 58.8% due to the suppression of surface cracks through strain transfer of the sample. From deep level emission and rocking curve measurements it was found that the threading dislocations play a more important role than oxygen vacancies for high-quality ZnO thin film growth.
Journal of Crystal Growth, 2009
High-quality zinc oxide (ZnO) films were successfully grown on ZnO-buffered a-plane sapphire (Al 2 O 3 (11 2 0)) substrates by controlling temperature for lateral growth using chemical bath deposition (CBD) at a low temperature of 60 1C. X-ray diffraction analysis and transmission electron microscopy micrographs showed that the ZnO films had a single-crystalline wurtzite structure with c-axis orientation. Rocking curves (o-scans) of the (0 0 0 2) reflections showed a narrow peak with full width at half maximum value of 0.501 for the ZnO film. A reciprocal space map indicated that the lattice parameters of the ZnO film (a ¼ 0.3250 nm and c ¼ 0.5207 nm) were very close to those of the wurtzitetype ZnO. The ZnO film on the ZnO-buffered Al 2 O 3 (11 2 0) substrate exhibited n-type conduction, with a carrier concentration of 1.9 Â 10 19 cm À3 and high carrier mobility of 22.6 cm 2 V À1 s À1 .
Dependence of film thickness on the structural and optical properties of ZnO thin films
Applied Surface Science, 2009
ZnO thin films are prepared on glass substrates by pulsed filtered cathodic vacuum arc deposition (PFCVAD) at room temperature. Optical parameters such as optical transmittance, reflectance, band tail, dielectric coefficient, refractive index, energy band gap have been studied, discussed and correlated to the changes with film thickness. Kramers–Kronig and dispersion relations were employed to determine the complex refractive index and dielectric constants using reflection data in the ultraviolet–visible–near infrared regions. Films with optical transmittance above 90% in the visible range were prepared at pressure of 6.5 × 10−4 Torr. XRD analysis revealed that all films had a strong ZnO (0 0 2) peak, indicating c-axis orientation. The crystal grain size increased from 14.97 nm to 22.53 nm as the film thickness increased from 139 nm to 427 nm, however no significant change was observed in interplanar distance and crystal lattice constant. Optical energy gap decreased from 3.21 eV to 3.19 eV with increasing the thickness. The transmission in UV region decreased with the increase of film thickness. The refractive index, Urbach tail and real part of complex dielectric constant decreased as the film thickness increased. Oscillator energy of as-deposited films increased from 3.49 eV to 4.78 eV as the thickness increased.
Solar Energy Materials and Solar Cells, 2010
Pulsed laser deposition Hall-Williamson plot ZnO/ITO/ZnO/ITO/ZnO multilayered thin films Nanostructured zinc oxide films Temperature-dependent electrical resistivity studies a b s t r a c t ZnO/ITO/ZnO/ITO/ZnO five layer thin films are fabricated by pulsed laser deposition on quartz substrate kept at a substrate temperature (T s ) 873 K at a background oxygen pressure (pO 2 ) of 0.05 mbar for different deposition duration for ZnO layers (5, 10, 15 and 20 min) while keeping a constant deposition time for ITO layers. The structural, optical and electrical properties of the as-deposited thin films have been investigated by GIXRD, AFM, UV-visible spectra, photoluminescence spectra and temperaturedependent electrical resistivity measurements (10-300 K) using four-probe technique. XRD patterns of the films show a polycrystalline nature. From the AFM images, the average grain size and mean surface roughness are estimated and the particles are densely packed in the film. A high transmittance is observed for all the films in the visible and IR region. The PL spectra show that the emission is in the UV and visible region due to the near band edge and deep level transitions of ZnO. The electrical resistivity of all the films are calculated and are very low compared to the reported values of as deposited ZnO thin films. The co-existence of very high transmittance in the visible region and very low dc resistivity enables these films suitable for optoelectronic device fabrications. The structural, optical and electrical studies reveal that ITO buffer layers improve the crystalline quality, optical and electrical properties of ZnO multilayered thin films.
Effect of Substrates on the Properties of ZnO Thin Films Grown by Pulsed Laser Deposition
Advances in Materials Physics and Chemistry, 2013
Polycrystalline zinc oxide (ZnO) thin films have been deposited at 450˚C onto glass and silicon substrates by pulsed laser deposition technique (PLD). The used source was a KrF excimer laser (248 nm, 25 ns, 5 Hz, 2 J/cm 2). The effects of glass and silicon substrates on structural and optical properties of ZnO films have been investigated. X-ray diffraction patterns showed that ZnO films are polycrystalline with a hexagonal wurtzite-type structure with a strong (103) orientation and have a good crystallinity on monocrystalline Si(100) substrate. The thickness and compositional depth profile were studied by Rutherford Backscattering spectrometry (RBS). The average transmittance of ZnO films deposited on glass substrate in the visible range is 70%.
Optical and structural properties of thin films of ZnO at elevated temperature
Zinc oxide (ZnO) thin films were prepared on glass substrate by sol-gel dip-coating method. The paper presents the properties of zinc oxide thin films deposited on soda-lime-glass substrate via dip-coating technique, using zinc acetate dehydrate and ethanol as raw materials. The effect of withdrawal speed on the crystalline structure, surface morphology and optical properties of the thin films has been investigated using XRD, SEM and UV-Vis spectrophotometer. X-ray diffraction study shows that all the films have hexagonal wurtzite structure with preferred orientation in (0 0 2) direction and transmission spectra showed highly transparent films with band gap ranging from 3.78 to 3.48 eV.
Structural characterization of ZnO thin films grown on various substrates by pulsed laser deposition
Journal of Physics D: Applied Physics, 2012
ZnO thin films were grown by pulsed laser deposition on three different substrates: sapphire (0 0 0 1), MgO (1 0 0) and fused silica (FS). The structure and morphology of the films were characterized by x-ray diffraction and scanning electron microscopy and defect studies were carried out using slow positron implantation spectroscopy (SPIS). Films deposited on all substrates studied in this work exhibit the wurtzite ZnO structure and are characterized by an average crystallite size of 20-100 nm. However, strong differences in the microstructure of films deposited on various substrates were found. The ZnO films deposited on MgO and sapphire single-crystalline substrates exhibit local epitaxy, i.e. a well-defined relation between film crystallites and the substrate. Domains with different orientation relationships with the substrate were found in both films. On the other hand, the film deposited on the FS substrate exhibits fibre texture with random lateral orientation of crystallites. Extremely high compressive in-plane stress of σ ∼ 14 GPa was determined in the film deposited on the MgO substrate, while the film deposited on sapphire is virtually stress-free, and the film deposited on the FS substrate exhibits a tensile in-plane stress of σ ∼ 0.9 GPa. SPIS investigations revealed that the concentration of open-volume defects in the ZnO films is substantially higher than that in a bulk ZnO single crystal. Moreover, the ZnO films deposited on MgO and sapphire single-crystalline substrates exhibit a significantly higher density of defects than the film deposited on the amorphous FS substrate.
Effect of buffer layer on solution deposited ZnO films
Materials Letters, 2005
ZnO films were prepared by solution deposition method on various substrates: bare glass, TiO2-buffer-coated glass, ITO glass and ZnO-buffer-coated glass. PEG addition was used to further investigate the effect of the patterned ZnO buffer on the morphology of the films. The structural morphology was investigated by using X-ray diffraction, scanning electron microscopy, field emission scanning electron microscopy analysis methods. The