| 1. |
- Amloy, Supaluck, et al.
(författare)
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Excitons and biexcitons in InGaN quantum dot like localization centers
- 2014
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 25:49, s. 495702-
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Tidskriftsartikel (refereegranskat)abstract
- Indium segregation in a narrow InGaN single quantum well creates quantum dot (QD) like exciton localization centers. Cross-section transmission electron microscopy reveals varying shapes and lateral sizes in the range ∼1–5 nm of the QD-like features, while scanning near field optical microscopy demonstrates a highly inhomogeneous spatial distribution of optically active individual localization centers. Microphotoluminescence spectroscopy confirms the spectrally inhomogeneous distribution of localization centers, in which the exciton and the biexciton related emissions from single centers of varying geometry could be identified by means of excitation power dependencies. Interestingly, the biexciton binding energy (Ebxx) was found to vary from center to center, between 3 to −22 meV, in correlation with the exciton emission energy. Negative binding energies are only justified by a three-dimensional quantum confinement, which confirms QD-like properties of the localization centers. The observed energy correlation is proposed to be understood as variations of the lateral extension of the confinement potential, which would yield smaller values of Ebxx for reduced lateral extension and higher exciton emission energy. The proposed relation between lateral extension and Ebxx is further supported by the exciton and the biexciton recombination lifetimes of a single QD, which suggest a lateral extension of merely ∼3 nm for a QD with strongly negative Ebxx = −15.5 meV.
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| 2. |
- Chen, Yen-Ting, et al.
(författare)
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Nucleation of single GaN nanorods with diameters smaller than 35 nm by molecular beam epitaxy
- 2013
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 103:20, s. 203108-
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Tidskriftsartikel (refereegranskat)abstract
- Nucleation mechanism of catalyst-free GaN nanorod grown on Si(111) is investigated by the fabrication of uniform and narrow (andlt; 35 nm) nanorods without a pre-defined mask by molecular beam epitaxy. Direct evidences show that the nucleation of GaN nanorods stems from the sidewall of the underlying islands down to the Si(111) substrate, different from commonly reported ones on top of the island directly. Accordingly, the growth and density control of the nanorods is exploited by a "narrow-pass" approach that only narrow nanorod can be grown. The optimal size of surrounding non-nucleation area around single nanorod is estimated as 88 nm.
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| 3. |
- Hsiao, Ching-Lien, et al.
(författare)
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Composition tunable Al1-xInxN nanorod arrays grown by ultra-high-vacuum magnetron sputter epitaxy
- 2011
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Self-assembled ternary Al1-xInxN nanorod arrays with variable In concentration, 0.10 ≤ x ≤ 0.32 have been realized onto c-plane sapphire substrates by ultra-high-vacuum magnetron sputter epitaxy with Ti0.21Zr0.79N or VN seed layers assistance. The formation of nanorods was very sensitive to the applied seed layer. Without proper seed layer assistance a continuous Al1-xInxN film was grown. The nanorods exhibit hexagonal crosssections with preferential growth along the c axis. A coaxial rod structure with higher In concentration in the core was observed by (scanning) transmission electron microscopy in combination with low-loss electron energy loss spectroscopy and energy dispersive xray spectroscopy. 5 K cathodoluminescence spectroscopy of Al0.86In0.14N nanorods revealed band edge emission at ~5.46 eV, which was accompanied by a strong defectrelated emission at ~ 3.38 eV.
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| 4. |
- Hsiao, Ching-Lien, et al.
(författare)
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Curved-lattice epitaxial growth of chiral AlInN twisted nanorods for optical applications
- 2012
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Despite of using chiral metamaterials to manipulate light polarization states has been demonstrated their great potential for applications such as invisible cloaks, broadband or wavelength-tunable circular polarizers, microreflectors, etc. in the past decade [1-6], operating wavelength in ultraviolet-visible range is still a challenge issue. Since these chiral structures often consist of metallic materials, their operation is designed for the infrared and microwave regions [2-4]. Here, we show how a controlled curved-lattice epitaxial growth (CLEG) of wide-bandgap AlInN semiconductor curved nanocrystals [7] can be exploited as a novel route for tailoring chiral nanostructures in the form of twisted nanorods (TNRs). The fabricated TNRs are shown to reflect light with a high degree of polarization as well as a high degree of circular polarization (that is, nearly circularly polarized light) in the ultravioletvisible region. The obtained polarization is shown to be dependent on the handedness of the TNRs.
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| 5. |
- Hsiao, Ching-Lien, et al.
(författare)
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Room-temperature heteroepitaxy of single-phase Al1-xInxN films with full composition range on isostructural wurtzite templates
- 2012
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 524, s. 113-120
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Tidskriftsartikel (refereegranskat)abstract
- Al1-xInxN heteroepitaxial layers covering the full composition range have been realized by magnetron sputter epitaxy on basal-plane AlN, GaN, and ZnO templates at room temperature (RT). Both Al1-xInxN single layers and multilayers grown on these isostructural templates show single phase, single crystal wurtzite structure. Even at large lattice mismatch between the film and the template, for instance InN/AlN (similar to 13% mismatch), heteroepitaxy is achieved. However, RT-grown Al1-xInxN films directly deposited on non-isostructural c-plane sapphire substrate exhibit a polycrystalline structure for all compositions, suggesting that substrate surface structure is important for guiding the initial nucleation. Degradation of Al1-xInxN structural quality with increasing indium content is attributed to the formation of more point-and structural defects. The defects result in a prominent hydrostatic tensile stress component, in addition to the biaxial stress component introduced by lattice mismatch, in all RT-grown Al1-xInxN films. These effects are reflected in the measured in-plane and out-of-plane strains. The effect of hydrostatic stress is negligible compared to the effects of lattice mismatch in high-temperature grown AlN layers thanks to their low amount of defects. We found that Vegards rule is applicable to determine x in the RT-grown Al1-xInxN epilayers if the lattice constants of RT-sputtered AlN and InN films are used instead of those of the strain-free bulk materials.
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| 6. |
- Hsiao, Ching-Lien, et al.
(författare)
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Spontaneous Formation of AlInN Core–Shell Nanorod Arrays by Ultrahigh-Vacuum Magnetron Sputter Epitaxy
- 2011
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Ingår i: Applied Physics Express. - : Japan Society of Applied Physics. - 1882-0786. ; 4:115002
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Tidskriftsartikel (refereegranskat)abstract
- The spontaneous formation of AlInN core–shell nanorod arrays with variable In concentration has been realized by ultrahigh-vacuum magnetron sputter epitaxy with Ti0.21Zr0.79N or VN seed layer assistance. The nanorods exhibit hexagonal cross sections with preferential growth along the c-axis. A core–shell rod structure with a higher In concentration in the core was observed by (scanning) transmission electron microscopy in combination with low-loss electron energy loss spectroscopy and energy dispersive X-ray spectroscopy. 5 K cathodoluminescence spectroscopy of Al0.86In0.14N nanorods revealed band edge emission at ∼5.46 eV, which was accompanied by a strong defect-related emission at ∼3.38 eV
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| 7. |
- Jokubavicius, Valdas, et al.
(författare)
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Macrodefects in cubic silicon carbide crystals
- 2010
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Ingår i: Materials Science Forum, Vols. 645-648. - : Transtec Publications; 1999. ; , s. 375-378
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Konferensbidrag (refereegranskat)abstract
- Different sublimation growth conditions of 3C-SiC approaching a bulk process have been investigated with the focus on appearance of macrodefects. The growth rate of 3C-SiC crystals grown on 6H-SiC varied from 380 to 460 mu m/h with the thickness of the crystals from 190 to 230 mu m, respectively. The formation of macrodefects with void character was revealed at the early stage of 3C-SiC crystal growth. The highest concentration of macrodefects appears in the vicinity of the domain in samples grown under high temperature gradient: and fastest temperature ramp up. The formation of macrodefects was related to carbon deficiency which appear due to high Si/C ratio which is used to enable formation of the 3C-SiC polytype.
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| 8. |
- Jouanny, I, et al.
(författare)
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In situ transmission electron microscopy studies of the kinetics of Pt-Mo alloy diffusion in ZrB2 thin films
- 2013
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 103:12
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Tidskriftsartikel (refereegranskat)abstract
- Using in situ high-temperature (1073–1173 K) transmission electron microscopy, we investigated the thermal stability of Pt and Mo in contact with polycrystalline ZrB2 thin films deposited on Al 2O3(0001). During annealing, we observed the diffusion of cubic-structured Pt1− x Mo x (with x = 0.2 ± 0.1) along the length of the ZrB2 layer. From the time-dependent increase in diffusion lengths, we determined that the Pt1− x Mo x does not react with ZrB2, but diffuses along the surface with a constant temperature-dependent velocity. We identify the rate-limiting step controlling the observed phenomenon as the flux of Mo atoms with an associated activation barrier of 3.8 ± 0.5 eV.
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| 9. |
- Junaid, Muhammad, et al.
(författare)
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Electronic-grade GaN(0001)/Al2O3(0001) grown by reactive DC-magnetron sputter epitaxy using a liquid Ga target
- 2011
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Ingår i: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 98:14, s. 141915-
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Tidskriftsartikel (refereegranskat)abstract
- Electronic-grade GaN (0001) epilayers have been grown directly on Al2O3 (0001) substrates by reactive DC-magnetron sputter epitaxy (MSE) from a liquid Ga sputtering target in an Ar/N2 atmosphere. The as-grown GaN epitaxial film exhibit low threading dislocation density on the order of ≤ 1010 cm-2 obtained by transmission electron microscopy and modified Williamson-Hall plot. X-ray rocking curve shows narrow fullwidth at half maximum (FWHM) of 1054 arcsec of the 0002 reflection. A sharp 4 K photoluminescence peak at 3.474 eV with a FWHM of 6.3 meV is attributed to intrinsic GaN band edge emission. The high structural and optical qualities indicate that MSEgrown GaN epilayers can be used for fabricating high-performance devices without the need of any buffer layer.
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| 10. |
- Khatibi, Ali, et al.
(författare)
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Face-Centered Cubic (Al1-xCrx)2O3
- 2011
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 519:8, s. 2426-2429
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of a face-centered cubic (Al1−xCrx)2O3 solid solution [0.60bxb0.70] in films grownonto Si substrates using reactive radio frequency magnetron sputtering from Al and Cr targets at 400 °C. Theproposed structure is NaCl-like with 33% vacancies on the metal sites. The unit cell parameter is 4.04 Å asdetermined by X-ray diffraction. The films have a b100N preferred crystallographic orientation and exhibithardness values up to 26 GPa and an elastic modulus of 220–235 GPa.
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