| 1. |
- Khranovskyy, V., et al.
(författare)
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Conductivity increase of ZnO : Ga films by rapid thermal annealing
- 2007
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Ingår i: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 42:1-6, s. 379-386
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Tidskriftsartikel (refereegranskat)abstract
- Due to a constant increase in demands for transparent electronic devices the search for alternative transparent conducting oxides (TCO) is a major field of research now. New materials should be low-cost and have comparable or better optical and electrical characteristics in comparison to ITO. The use of n-type ZnO was proposed many years ago, but until now the best n-type dopant and its optimal concentration is still under discussion. Ga was proposed as the best dopant for ZnO due to similar atomic radius of Ga3+ compared to Zn2+ and its lower reactivity with oxygen. The resistivity ρ of ZnO:Ga/Si (100) films grown by PEMOCVD was found to be 3×10-2 Ω cm. Rapid thermal annealing (RTA) was applied to increase the conductivity of ZnO:Ga (1 wt%) films and the optimal regime was determined to be 800 {ring operator}C in oxygen media for 35 s. The resistivity ratio ρbefore / ρafter before and after the annealing and the corresponding surface morphologies were investigated. The resistivity reduction (ρbefore / ρafter ≈ 80) was observed after annealing at optimal regime and the final film resistivity was approximately ≈4×10-4 Ω cm, due to effective Ga dopant activation. The route mean square roughness (Rq) of the films was found to decrease with increasing annealing time and the grain size has been found to increase slightly for all annealed samples. These results allow us to prove that highly conductive ZnO films can be obtained by simple post-growth RTA in oxygen using only 1% of Ga precursor in the precursor mix. © 2007 Elsevier Ltd. All rights reserved.
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| 2. |
- Khranovskyy, V., et al.
(författare)
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Improvement of ZnO thin film properties by application of ZnO buffer layers
- 2007
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 308:1, s. 93-98
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Tidskriftsartikel (refereegranskat)abstract
- 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 Ts=300 °C and the main layer at Ts=500 °C, high-temperature ZnO buffer layer deposited at Ts=500 °C and the main layer at Ts=300 °C. For comparison, a sample grown at high-temperature Ts=500 °C by one-step procedure was used. The low-temperature 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=0.07°) 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. © 2007 Elsevier B.V. All rights reserved.
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| 3. |
- Khranovskyy, V., et al.
(författare)
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Morphology, electrical and optical properties of undoped ZnO layers deposited on silicon substrates by PEMOCVD
- 2008
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 516:7, s. 1396-1400
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Tidskriftsartikel (refereegranskat)abstract
- The goal of this work is to investigate the morphology, electrical and optical properties of undoped ZnO (i-ZnO) thin layers deposited on Si substrates with (100) and (111) orientations. Plasma enhanced metalorganic chemical vapor deposition (PEMOCVD) was used for the deposition of i-ZnO layers at different temperatures. Atomic force microscopy (AFM), ellipsometry and four-probe method were used for the analysis. It is found that substrate orientation and growth temperature determine the morphological (grains size, surface roughness) as well as electrical properties of ZnO films. It is shown that the refractive index value depends on the surface morphology. It is concluded that properties of i-ZnO layers deposited on different Si substrates at different conditions exhibit some trends and peculiarities, which have to be taken into account for the processing of heterojunction solar cells by the PEMOCVD method. © 2007 Elsevier B.V. All rights reserved.
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| 4. |
- Khranovskyy, V., et al.
(författare)
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PEMOCVD of ZnO thin films, doped by Ga and some of their properties
- 2006
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Ingår i: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 39:1-4, s. 275-281
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Tidskriftsartikel (refereegranskat)abstract
- Zinc oxide (ZnO) is a promising semiconductor material with a great variety of applications, for example for highly conductive films for transparent electronics. Recently, Ga has been proposed as a dopant, exhibiting the advantages of a very similar atomic radius compared to Zn, a smaller reactivity, and a higher resistivity to oxidation compared to its competitor Al. In this study ZnO films, doped by Ga, were produced on Al2O3(0001) substrates by PEMOCVD. The doping was realized with 1, 3, 5 and 10 wt% gallium precursor content in the mixture. The resistivity of the prepared films, as well as the morphology and the transmittance, was investigated. All the deposited films have demonstrated a high optical transmittance above 93% in the range between 400 and 800 nm. A strong correlation between the electrical resistivity and the optical band gap depending on the Ga content was observed. An AFM analysis demonstrated highly uniform and smooth surfaces. The average grain size and route mean square roughness decreased with increasing Ga content. © 2005 Elsevier Ltd. All rights reserved.
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| 5. |
- Khranovskyy, V., et al.
(författare)
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Structural and morphological properties of ZnO : Ga thin films
- 2006
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:2 SPEC. ISS., s. 472-476
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Tidskriftsartikel (refereegranskat)abstract
- Zinc oxide (ZnO) is a promising semiconductor material with a great variety of applications. Compared to undoped ZnO, impurity-doped ZnO has a lower resistivity and better stability. With this aim, Ga has been proposed as a dopant. In this study, the structural characteristics and surface morphology of ZnO films produced by PEMOCVD at a substrate temperature of 250 °C on the c-plane (001) of sapphire were investigated. Doping was realized with 1, 3, 5 and 10 wt.% of Ga2(AA)3 in the precursor's mixture. At lower contents, Ga stimulates growth of (002) oriented textured films and the smallest FWHM was obtained as low as 0.17° for ZnO:Ga with 1 wt.%. A change in preferential orientation as well as surface smoothing and roughness decreasing of the films were observed with further increasing Ga content in precursor's mixture. We assume a key role of Ga and note that such a feature would be beneficial for the application of ZnO thin films for formation of abrupt junctions in p-n device structures. © 2005 Elsevier B.V. All rights reserved.
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| 6. |
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| 7. |
- Ievtushenko, A., et al.
(författare)
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Effect of Ag doping on the structural, electrical and optical properties of ZnO grown by MOCVD at different substrate temperatures
- 2018
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Ingår i: Superlattices and Microstructures. - : ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD. - 0749-6036 .- 1096-3677. ; 117, s. 121-131
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Tidskriftsartikel (refereegranskat)abstract
- ZnO films and nanostructures were deposited on Si substrates by MOCVD using single source solid state zinc acetylacetonate (Zn(AA)) precursor. Doping by silver was realized in-situ via adding 1 and 10 wt. % of Ag acetylacetonate (Ag(AA)) to zinc precursor. Influence of Ag on the microstructure, electrical and optical properties of ZnO at temperature range 220-550 degrees C was studied by scanning, transmission electron and Kelvin probe force microscopy, photoluminescence and four-point probe electrical measurements. Ag doping affects the ZnO microstructure via changing the nucleation mode into heterogeneous and thus transforming the polycrystalline films into a matrix of highly c-axis textured hexagonally faceted nanorods. Increase of the work function value from 4.45 to 4.75 eV was observed with Ag content increase, which is attributed to Ag behaviour as a donor impurity. It was observed, that near-band edge emission of ZnO NS was enhanced with Ag doping as a result of quenching deep-level emission. Upon high doping of ZnO by Ag it tends to promote the formation of basal plane stacking faults defect, as it was observed by HR TEM and PL study in the case of 10 wt.% of Ag. Based on the results obtained, it is suggested that NS deposition at lower temperatures (220-300 degrees C) is more favorable for p-type doping of ZnO. (C) 2018 Elsevier Ltd. All rights reserved.
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| 8. |
- Ievtushenko, A, et al.
(författare)
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Ultraviolet Detectors Based on ZnO : N Thin Films with Different Contact Structures
- 2008
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Ingår i: Acta Physica Polonica. A. - 0587-4246 .- 1898-794X. ; 114:5, s. 1123-1129
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Tidskriftsartikel (refereegranskat)abstract
- Al/ZnO:N/Al and Ni/ZnO:N/Al diode photodetectors fabricated by do magnetron sputtering of ZnO:N films on p-Si substrates are studied. The photocurrent-to-dark current ratio equal to 250 at lambda = 390 nm and the time constant of photoresponse about 10 mu s for Al/ZnO:N/Al structures with 4 mu m interdigital spacing was achieved. The Ni/ZnO:N/Al diode structure has the rectification ratio approximate to 10(2) at bias 1 V, the maximal responsivity about 0.1 A/W is observed at 365 nm, and the measured time constant of photoresponse is about 100 ns.
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| 9. |
- Karpyna, V A, et al.
(författare)
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Electron field emission from ZnO self-organized nanostructures and doped ZnO : Ga nanostructured films
- 2009
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Ingår i: Microelectronics Journal. - : Elsevier BV. - 0959-8324 .- 0026-2692. ; 40:2, s. 229-231
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Tidskriftsartikel (refereegranskat)abstract
- Self-organized ZnO nanostructures were grown by thermal decomposition of metalorganic precursors as well as by carbothermal reduction process. Nanostructured undoped and gallium-doped ZnO nanostructured films were deposited by plasma-enhanced chemical vapor deposition from metalorganic compounds. Electron field emission follows Fowler-Nordheim equation. Efficient electron emission was obtained from self-organized nanorstructures due to their geometric shape. Enhanced field emission from ZnO:Ga nanorstructured films in comparison with undoped ZnO films is obliged to lowering work function at doping by gallium.
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| 10. |
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| 11. |
- Khranovskyy, Volodymyr, et al.
(författare)
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Investigation of ZnO as a perspective material for photonics
- 2008
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 205:1, s. 144-149
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Tidskriftsartikel (refereegranskat)abstract
- Emissive properties of ZnO are of great interests in terms of the UV LED device design. The persistent "green" luminescence due to deep defect is an obstacle for obtaining an intense UV emission, expected from ZnO. We report the positive role of thermally diffused H toward quenching the defect emission in ZnO. It is suggested that hydrogen passivates defects responsible for DLE, resulting in efficient near band edge luminescence. As-grown ZnO/SiNx :H/Si films, deposited at 350 degrees C demonstrate intense narrow peaks of UV emission at 380 nm and a ratio of emission intensities, NBE/DLE approximate to 42. [GRAPHICS]
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| 12. |
- Khranovskyy, Volodymyr, et al.
(författare)
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Luminescence anisotropy of ZnO microrods
- 2012
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Ingår i: Journal of Luminescence. - : Elsevier. - 0022-2313 .- 1872-7883. ; 132:10, s. 2643-2647
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Tidskriftsartikel (refereegranskat)abstract
- The local features of light emission from ZnO microrods were studied: it is revealed that ZnO luminescence spectra are significantly influenced by the crystal morphology. It is shown that the near and edge ultraviolet emission occurs primarily from the top (0001) planes of ZnO microrods; while the defect related visible emission was found to occur dominantly from the side facets. The room temperature cathodoluminescence analysis revealed that visible emission consists of a few overlapping peaks, arising due to recombination on common points and surface defects (Zn-i, V-o, V-o(O)/V-o(**) V-o(**) and surface defects.). While at low temperature, only the luminescence due to neutral donor bound exciton ((DX)-X-0) emission is observed. The data obtained suggest that the light emission spectra of ZnO material of diverse morphology cannot be directly compared, although some common spectral features are present.
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| 13. |
- Shtepliuk, I, et al.
(författare)
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Electrical properties of n-Zn0.94Cd0.06O/p-SiC heterostructures
- 2013
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Ingår i: Solid-State Electronics. - : Elsevier BV. - 0038-1101 .- 1879-2405. ; 81, s. 72-77
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Tidskriftsartikel (refereegranskat)abstract
- We report the low-temperature (250 °C) fabrication of n-ZnCdO/p-SiC heterostructures by direct current magnetron sputtering (DC MS) technique. As-grown heterostructures exhibit diode characteristics: current–voltage measurements showed a typical rectifying characteristic of a p–n junction and the presence of series resistance. It is found that the turn-on voltage of heterostructures depends on the acceptor concentration in p-SiC. Via Cd doping of ZnO the energy barrier for holes can be lowered, which promotes the hole injection from the p-type layer to the n-type layer as well as favors the radiative recombination in the n-ZnCdO layer.
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| 14. |
- Shtepliuk, I., et al.
(författare)
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Phase Field Modeling of the Zn1-xCdxO Solid Solutions
- 2014
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Ingår i: Acta Physica Polonica. A. - : POLISH ACAD SCIENCES INST PHYSICS. - 0587-4246 .- 1898-794X. ; 126:5, s. 1079-1082
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Tidskriftsartikel (refereegranskat)abstract
- The analysis of spinodal decomposition in the Zn1-xCdxO ternary alloy was carried out by means of the nonlinear Cahn-Hilliard equation. Interaction parameter as a function of composition x was provided by valence force field simulations and was used in this analysis. The morphological patterns for the ternary alloys with different Cd content (x = 5, 10, 50%) were experimentally obtained using the semi-implicit Fourier-spectral method. The simulated microstructure evolution Zn0.95Cd0.05O demonstrates that the microstructure having a form of bicontinuous worm-like network is evolved with the progress of aging. An effect of the phase-field mobility and the gradient energy on the microstructure evolution of the Zn1-xCdxO alloys is discussed. It was found that the higher driving force for the decomposition in the higher Cd content film results in a higher decomposition rate revealed by the simulations. The temporal evolution of the simulated Zn0.95Cd0.05O microstructure is in good agreement with experimental results, which have been obtained for this solid solution.
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| 15. |
- Shtepliuka, I., et al.
(författare)
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Microstructure and luminescence dynamics of ZnCdO films with high Cd content deposited on different substrates by DC magnetron sputtering method
- 2013
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 276, s. 550-557
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Tidskriftsartikel (refereegranskat)abstract
- Investigation of Cd behavior in the ZnCdO alloys, where Cd content exceeds the solubility limit, is of importance due to possible impurity segregation and second phases' formation in this material. We have studied the Cd behavior in the Zn1-xCdxO films deposited by dc magnetron sputtering on different substrates: c-plane Al2O3, bare Si (1 0 0) and Au (45 nm)/Si (1 0 0). It is revealed that Cd content of 10 at. % in the target results in average 6-8 at. % of Cd in the films, depending on the substrate type. Structural analysis based on X-ray diffraction revealed the absence of Cd-related secondary phases. Time-resolved photoluminescence (TRPL) and high-resolution energy dispersive X-ray analysis (EDX) help to understand the recombination dynamics of spontaneous emission and to establish correlations between cadmium content and radiative lifetime. We have revealed that the internal quantum efficiency is influenced by the Cd content and defect concentration. It is suggested that increasing of the cadmium content results in the reduction of nonradiative recombination centers originating from point defects.
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