influnce of homo buffer layer thickness of ZnO epilayer (original) (raw)
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Improvement in the crystallinity of ZnO thin films by introduction of a buffer layer
Thin Solid Films, 2002
The influence of pre-deposition of homo-buffer layers on film quality is studied as functions of temperature and duration of pre-deposition, for zinc oxide (ZnO) crystalline films prepared by pulsed laser deposition on sapphire (0 0 0 1) substrates. This preparation technique is necessary to prepare high quality films suitable for the development of ZnO devices. Crystallinity and surface morphology were characterized by X-ray diffraction (XRD), reflection high energy electron diffraction and scanning electron microscopy. The line width of the rocking curve observed for ZnO (0 0 0 2) XRD of ZnO films decreases (to 0.098 from 0.2-0.38) upon introduction of a buffer layer of ZnO itself at a low temperature approximately 500 8C, indicating the formation of high quality films. The surface morphology and flatness were also improved. The film prepared under optimal conditions shows a high optical transmittance of ;90% with a steep falloff at 380 nm and a fairly small carrier concentration (1.8=10 17 cm ). These results imply that the buffer layer relaxes the strain due to lattice mismatch between ZnO and sapphire (by 18%) y3 and improves the film crystallinity. ᮊ
Ultra-smooth and Lattice relaxed ZnO thin films N. Fouda, El Shazly M. Duraia, E.A. Eid
The crystal structure and quality of ZnO thin films were enhanced by high temperature vacuum annealing. High quality ZnO thin films have been grown on a-plane sapphire substrate by radio frequency (rf) magnetron sputtering method at a substrate temperature of 600 ° C. A remarkable improvement in the epilayer quality were established by in situ high temperature annealing. The film quality, smoothness, the in plane stress, and the degree of epitaxyof the films have been evaluated. The crystalline quality was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy analyses. An extremely smooth ZnO films were achieved at higher annealing temperatures with root mean square roughness of 0.3nm. The transverse optical mode A1(TO) observed in all the samples and the longitudinal optical mode A1(LO) appeared only at higher annealing temperatures over 800 ° C in the mico-Raman scattering measurements. The strain of c-axis were relaxed and the lattice parameter was comparable to that of bulk ZnO at high annealing temperature of 900 ° C. Keywords: Zinc oxide thin films; vacuum annealing; lattice relaxation; Raman spectroscopy
A comprehensive review of ZnO materials and devices
Journal of Applied Physics, 2005
The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60 meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. Lett. 16, 439 (1970)]. In terms of devices, Au Schottky barriers in 1965 by Mead [Phys. Lett. 18, 218 (1965)], demonstration of light-emitting diodes (1967) by Drapak [Semiconductors 2, 624 (1968)], in which Cu2O was used as the p-type material, metal-insulator-semiconductor structures (1974) by Minami et al. [Jpn. J. Appl. Phys. 13, 1475 (1974)], ZnO/ZnSe n-p junctions (1975) by Tsurkan et al. [Semiconductors 6, 1183 (1975)], and Al/Au Ohmic contacts by Brillson [J. Vac. Sci. Technol. 15, 1378 (1978)] were attained. The main obstacle to the development of ZnO has been the lack of reproducible and low-resistivity p-type ZnO, as recently discussed by Look and Claflin [Phys. Status Solidi B 241, 624 (2004)]. While ZnO already has many industrial applications owing to its piezoelectric properties and band gap in the near ultraviolet, its applications to optoelectronic devices has not yet materialized due chiefly to the lack of p-type epitaxial layers. Very high quality what used to be called whiskers and platelets, the nomenclature for which gave way to nanostructures of late, have been prepared early on and used to deduce much of the principal properties of this material, particularly in terms of optical processes. The suggestion of attainment of p-type conductivity in the last few years has rekindled the long-time, albeit dormant, fervor of exploiting this material for optoelectronic applications. The attraction can simply be attributed to the large exciton binding energy of 60 meV of ZnO potentially paving the way for efficient room-temperature exciton-based emitters, and sharp transitions facilitating very low threshold semiconductor lasers. The field is also fueled by theoretical predictions and perhaps experimental confirmation of ferromagnetism at room temperature for potential spintronics applications. This review gives an in-depth discussion of the mechanical, chemical, electrical, and optical properties of ZnO in addition to the technological issues such as growth, defects, p-type doping, band-gap engineering, devices, and nanostructures.
Growth of epitaxial p-type ZnO thin films by codoping of Ga and N
Applied Physics Letters, 2006
Codoping of Ga and N was utilized to realize p-type conduction in ZnO films using rf magnetron sputtering. The films obtained at 550°C on sapphire showed resistivity and hole concentrations of 38 ⍀ cm and 3.9ϫ 10 17 cm −3 , respectively. ZnO films also showed a p-type behavior on p-Si with better electrical properties. ZnO homojunctions synthesized by in situ deposition of Ga-N codoped p-ZnO layer on Ga doped n-ZnO layer showed clear p-n diode characteristics. Low temperature photoluminescence spectra of codoped films also revealed a dominant peak at 3.12 eV. The codoped films showed a dense columnar structure with a c-axis preferred orientation.
Journal of Alloys and Compounds, 2011
ZnO thin films were deposited by ultrasonic spray technique, zinc acetate was used as starting solution with a molarity of 0.1 M. A set of indium (In) doped ZnO (between 2 and 8 wt%) thin films were grown on glass substrate at 350 • C. The present work is focused on the influence of the doping level on the structural, optical and electrical films properties. Optical film characterization was carried by using UV-visible transmission spectroscopy, the optical gap was deduced from absorption. From X ray diffraction (XRD) analysis, we have deduced that ZnO films are formed with nanocrystalline structure with preferential (0 0 2) orientation. The grain size is increased with In doping from 28 to 37 nm. Electrical characterization was achieved using two-probes coplanar structure, the measured conductivity varies from 2.3 to 5.9 cm −1 when increasing the doping level. However the optical gap is reduced from 3.4 to 3.1 eV.
THE Coatings, 2021
ZnO thin films were synthesized on silicon and glass substrates using the plasma-enhanced chemical vapor deposition (PECVD) technique. Three samples were prepared at substrates temperatures of 200, 300, and 400 °C. The surface chemical composition was analyzed by the use of X-Ray Photoelectron spectroscopy (XPS). Structural and morphological properties were studied by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Optical properties were carried out by UV-visible spectroscopy. XPS spectra showed typical peaks of Zn(2p3/2), Zn(2p1/2), and O(1s) of ZnO with a slight shift attributed to the substrate temperature. XRD analysis revealed hexagonal wurtzite phases with a preferred (002) growth orientation that improved with temperature. Calculation of grain size and dislocation density revealed the crystallization improvement of ZnO when the substrate temperature varied from 200 to 400 °C. SEM images of ZnO films showed textured surfaces composed of grains of spheric...
Characterization of ZnO Thin Films
2000
ZnO is a strategic material for various photonic applications. We present our results on characterization of thin films of ZnO grown by sol-gel spin and RF sputtering methods. The characterization techniques involved ellipsometry, scanning electron microscopy with energy dispersive analysis, X-ray diffraction and scanning tunneling microscopy. Microstructural characterization of the films using zinc nitrate precursor has delineated many interesting features
Nano and micro structural studies of thin films of ZnO
Journal of Materials Science, 2006
Zinc oxide thin films grown by sol-gel and RF sputtering methods have been characterized. The characterization techniques used involve ellipsometry, optical absorption, scanning tunneling microscopy, scanning and transmission electron microscopy. The films grown by sol-gel spin method which followed zinc acetate route exhibited a smoother texture than the films, which were deposited by using zinc nitrate route. The later type of films showed a dendritic character. Nano-structured fine grains of size ranging from 20 to 60 nm were observed with zinc nitrate precursor film. Individual grains show a sharp contrast with different facets and boundaries. Crystal planes and lattice parameters calculated by electron diffraction and X-ray diffraction are quite close and in agreement with the reported values in literature. Scanning tunneling microscopy has been used for measuring the average roughness of the surface and estimating the lattice constants. The STM studies of RF sputtered films, although showing a ZnO structure, exhibited a disturbed lattice. This was presumably due to the fact that after deposition the films were not annealed. Nanographs of 2D and 3D view of atomic positions of ZnO have been presented by using scanning tunneling microscopy.