| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
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| 8. |
- 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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| 9. |
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| 10. |
- 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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