| 1. |
- Kamiyama, Satoshi, et al.
(författare)
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White light-emitting diode based on fluorescent SiC
- 2012
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 522, s. 23-25
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Tidskriftsartikel (refereegranskat)abstract
- A monolithic white light-emitting diode (LED,) comprising a combination of a fluorescent-SiC (f-SiC) substrate and a nitride-based near-UV LED stack, is proposed. On the basis of the recombination of donor and acceptor pairs, the f-SiC substrate works as a phosphor for visible light emission. By employing the Fast Sublimation Growth Process method, the high-quality f-SiC substrate doped with N and B exhibited a nonradiative carrier lifetime of 55 mu s and an internal quantum efficiency (IQE) of 40%. With increasing donor and acceptor doping concentrations, a high IQE was estimated even at a high excitation level.
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| 2. |
- Khranovskyy, Volodymyr, et al.
(författare)
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Effect of oxygen exposure on the electrical conductivity and gas sensitivity of nanostructured ZnO films
- 2009
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 517:6, s. 2073-2078
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructured ZnO films (Undoped and Ga, Co, Mn doped) were exposed to oxygen (1-80 vol.%) at temperature range of 300-500 degrees C in order to reveal the ambience-temperature effect oil the electrical conductivity. The dominant effect of ambient influence via oxygen absorption was observed: the intensity of conductivity decrease was found to be proportional with temperature and tends to saturate with time. It is demonstrated that oxygen absorption occurs accordingly to diffusion law and the quantifying of oxygen diffusion was realized for different samples. It is revealed that the type of dopant affects the diffusion in ZnO and the tendency to increase the diffusion intensity with dopant content has been observed. After oxygen saturation the reversible effect of oxygen adsorption became dominant and contributed to the films conductivity. Oxygen exposure undoped ZnO films revealed high sensitivity for oxygen content change in the ambience therefore they have been preceded further for gas sensor design and the detailed investigation of films sensing properties has been carried out.
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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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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. |
- Pecz, B, et al.
(författare)
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Structural investigation of SiC epitaxial layers grown under microgravity and on-ground conditions
- 1999
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 357:2, s. 137-143
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Tidskriftsartikel (refereegranskat)abstract
- Thick 4H-, and 6H-SiC epitaxial layers have been grown by LPE from Si-Sc-C solvent at microgravity conditions during a space experiment, as well as on-ground. The samples are characterised by cross-sectional TEM and HRXRD. Layers grown at microgravity are relatively defect free, although their surfaces are always stepped. Control samples grown on-ground have similar surface appearance, but contain scandium carbide precipitates, nanopipes, micropipes and/or cavities as verified by TEM. However, none of the aforementioned defects was traced in the layers grown at microgravity conditions. So, samples grown at space microgravity conditions are superior in their defect structure to those ones grown on the ground. The defects called nanopipes can be described as empty pipes of about 200 nm diameter traversing the layer in the [0001] (growth) direction. The steps in the microgravity and on-ground samples have facets of {104} type crystallographic planes both in 6H-, and 4H-SiC. We suggest, that those facets are formed and preferred during growth due to a possible mechanism of decreasing the high energy of the growing Si terminated (0001) surface. (C) 1999 Elsevier Science S.A. All rights reserved.
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| 6. |
- Shtepliuk, Ivan, et al.
(författare)
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Effect of c-axis inclination angle on the properties of ZnO/Zn1-xCdxO/ZnO quantum wells
- 2016
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 603, s. 139-148
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Tidskriftsartikel (refereegranskat)abstract
- The development of optoelectronic devices based on highly-promising Zn1 - xCdxO semiconductor system demands deep understanding of the properties of the Zn1 - xCdxO-based quantum wells (QWs). In this regard, we carried out a numerical study of the polarization-related effects in polar, semi-polar and non-polar ZnO/ Zn1 - xCd xO/ZnO QWs with different parameters of the quantum well structure. The effects of well width, barrier thickness, cadmium content in the active layer and c-axis inclination angle on the distribution of the electron and hole wave function and transition energy were investigated using the 6 x 6 k center dot p Hamiltonian and one-dimensional self-consistent solutions of nonlinear Schrodinger-Poisson equations with consideration of spatially varying dielectric constant and effective mass. The strong sensitivity of the internal electric field, transition energy and overlap integral to cadmium content and well thickness in the angle range from 0 to 40 degrees was revealed. An unexpected change of the internal electric fields sign was observed at the angles ranging from 70 to 90 degrees. We also found a difference in the electronic properties between (0001)-, (11 (2) over bar2)-and (10 (1) over bar0)-oriented QWs.
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| 7. |
- Shtepliuk, Ivan, et al.
(författare)
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Theoretical study of O- and Zn-face polarity effect on the optical properties of the conventional and staggered ZnO/Zn1-xCdxO/ZnO quantum wells
- 2015
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 594, s. 323-327
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Tidskriftsartikel (refereegranskat)abstract
- In this work we present a comparative study of Zn-face and O-face polarity Zn1 - xCdxO-based conventional and staggered quantum-well (QW) structures. The calculation of optical properties of QWs was performed by means of self-consistent Schrodinger-Poisson solver with consideration of polarization-induced effects. The conventional Zn-face and O-face QWs possess similar values of transition energy and an overlap of electron and hole wave functions. A change of the polarity from Zn-face to O-face for the conventional QWs influences only a shape of the conduction and valence band edge profile. It is revealed that the utilization of the staggered QWs leads to an improvement of the confinement characteristics. In addition, the O-face staggered QW structure has larger values of transition energy and overlap integral compared to the Zn-face staggered QW structure. O-terminated staggered QW structure is less dependent on the well thickness and has lower sensitivity to Cd content in embedded Zn1 - xCdxO layer. Control of the material polarity and design of the staggered QWs provide cost-effective approach for engineering the QW band structures with enhanced QW performance. This enables constructing of the Zn1 - xCdxO-based light emission diodes with improved radiative efficiency emitting, applicable for solid state lighting. (C) 2015 Elsevier B.V. All rights reserved.
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| 8. |
- Sun, Jianwu, et al.
(författare)
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Room temperature luminescence properties of fluorescent SiC as white light emitting diode medium
- 2012
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 522, s. 33-35
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Tidskriftsartikel (refereegranskat)abstract
- The high quantum efficiency of donor–acceptor-pair emission in N and B co-doped 6H–SiC opens the way for SiC to constitute as an efficient light-emitting medium for white light-emitting diodes. In this work, we evidence room temperature luminescence in N and B co-doped 6H–SiC fluorescent material grown by the Fast Sublimation Growth Process. Three series of samples, with eight different N and B doping levels, were investigated. In most samples, from photoluminescence measurements a strong N–B donor–acceptor-pair emission band was observed at room temperature, with intensity dependent on the nitrogen pressure in the growth chamber and boron doping level in the source. Low temperature photoluminescence spectra showed that N bound exciton peaks exhibited a continuous broadening with increasing N2 pressure during the growth, unambiguously indicating an opportunity to control the N doping in the epilayer by conveniently changing the N2 pressure. Finally, the crystal quality of the N and B doped 6H–SiC was evaluated by X-ray diffraction measurements. The ω rocking curves of (0006) Bragg diffractions from the samples grown with lower and higher N2 pressure show almost the same value of the full width at half maximum as that collected from the substrate. This suggests that the N and B doping, which is expected to give rise to an efficient donor–acceptor-pair emission at room temperature, does not degrade the crystal quality.
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