| 1. |
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| 2. |
- Andreasson, Måns, 1975, et al.
(author)
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Organic molecular beam deposition system and initial studies of organic layer growth
- 2006
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In: Physica Scripta. - 1402-4896 .- 0031-8949. ; T126, s. 1-5
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Journal article (peer-reviewed)abstract
- This work describes an organic molecular beam deposition system with substrate entry/exitchamber, buffer chamber and with the possibility to transfer substrate from a III–V molecularbeam deposition system. Flux calibrations of organic molecules and the initial growth oforganic layers are described. For this purpose, the molecules 3,4,9,10 perylene tetra carboxylicdianhydride and copper phtalocyanine were used. Layers were grown on oxidized andhydrogen passivated Si(100), Indium tin oxide and glass respectively. The growth wasinvestigated with atomic force microscopy, reflection high energy electron diffraction andultraviolet photoemission spectroscopy. An investigation with x-ray photoelectron and Ramanspectroscopy on the effect of atmospheric exposure is also included, showing little effect ofsurface pollution when the samples were handled carefully. The initial formation (monolayers)of copper phtalocyanine thin films was studied by ultraviolet photoemission spectroscopy.
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| 3. |
- Adolph, David, 1971, et al.
(author)
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Plasma-assisted molecular beam epitaxy of ZnO on in-situ grown GaN/4H-SiC buffer layers
- 2015
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In: Frontiers of Materials Science. - : Springer Science and Business Media LLC. - 2095-025X .- 2095-0268. ; 9:2, s. 185-191
-
Journal article (peer-reviewed)abstract
- Plasma-assisted molecular beam epitaxy (MBE) was used to grow ZnO (0001) layers on GaN(0001)/4H-SiC buffer layers deposited in the same growth chamber equipped with both N- and O-plasma sources. The GaN buffer layers were grown immediately before initiating the growth of ZnO. Using a substrate temperature of 440 degrees C-445 degrees C and an O-2 flow rate of 2.0-2.5 sccm, we obtained ZnO layers with smooth surfaces having a root-mean-square roughness of 0.3 nm and a peak-to-valley distance of 3 nm shown by AFM. The FWHM for X-ray rocking curves recorded across the ZnO(0002) and ZnO(10 (1) over bar5) reflections were 200 and 950 arcsec, respectively. These values showed that the mosaicity (tilt and twist) of the ZnO film was comparable to corresponding values of the underlying GaN buffer. It was found that a substrate temperature > 450 degrees C and a high Zn-flux always resulted in a rough ZnO surface morphology. Reciprocal space maps showed that the in-plane relaxation of the GaN and ZnO layers was 82.3% and 73.0%, respectively and the relaxation occurred abruptly during the growth. Room-temperature Hall-effect measurements showed that the layers were intrinsically n-type with an electron concentration of 10(19) cm(-3) and a Hall mobility of 50 cm(2).V-1.s(-1).
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| 4. |
- Aggerstam, Thomas, et al.
(author)
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GaN/AlN multiple quantum well structures grown by MBE on GaN templates for 1.55 mu m intersubband absorption
- 2007
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In: Quantum Sensing and Nanophotonic Devices IV. - : SPIE. - 9780819465924 ; 6479, s. 64791E-
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Conference paper (peer-reviewed)abstract
- We have used MBE to grow MQW structures on MOVPE GaN/sapphire templates. The MQW devices are intended for high speed intersubband electroabsorption modulator devices operating at 1.55-mu m. The GaN/AlN multiple quantum well material was systematically studied regarding the surface morphology, structural characterization and optical property by atomic force microscopy, X-ray diffraction and Fourier transform infrared spectroscopy, respectively. The intersubband resonance energy was also calculated considering many-body effects in n-type doped structures. The multiple quantum well structure showed superior performance in terms of linewidth when grown on GaN templates as compared on sapphire. GaN quantum well and AlN barriers with a thickness of 3.3 and 4.2 nm respectively resulted in FWHM of the intersubband absorption peak as low as 93 meV at an absorption energy of 700 meV. This is promising for intersubband modulator applications.
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| 5. |
- Akabli, H., et al.
(author)
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Intersubband energies in Al1-yInyN/Ga1-xInxN heterostructures with lattice constant close to aGaN
- 2012
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In: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 52:1, s. 70-77
-
Journal article (peer-reviewed)abstract
- We have studied the conduction band profile and the intersubband transition energy, E-12, of Al1-yInyN/Ga1-xInxN quantum well structures. We have considered how material parameters such as non-parabolicity and the uncertainty in the bowing parameter affect E-12 and the corresponding wavelength, lambda(12). The calculations include strain and cover the transition range from telecommunication wavelengths (1.55 mu m) to the mid-infrared (similar to 10 mu m). Our results show that the transition energies of strain-free Al1-yInyN/Ga1-xInxN quantum well structures, which are lattice-matched to GaN (y = 17.7%, x = 0), resulted in wavelengths above similar to 2 mu m. To reach shorter wavelengths, we explored structures with other indium concentrations but maintaining a small mismatch to GaN. For similar to 1% lattice mismatch the wavelength lambda(12) could be reduced to less than 1.55 mu m. The results serve as a starting point for designing and epitaxial growth of photonic intersubband structures.
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| 6. |
- Amloy, Supaluck, et al.
(author)
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On the polarized emission from exciton complexes in GaN quantum dots
- 2012
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In: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 100:021901
-
Journal article (peer-reviewed)abstract
- The optical linear polarization properties of exciton complexes in asymmetric Stranski-Krastanov grown GaN quantum dots have been investigated experimentally and theoretically. It is demonstrated that the polarization angle and the polarization degree can be conveniently employed to associate emission lines in the recorded photoluminescence spectra to a specific dot. The experimental results are in agreement with configuration interaction computations, which predict similar polarization degrees for the exciton and the biexciton (within 10%) in typical GaN quantum dots. The theory further predicts that the polarization degree can provide information about the charge state of the dot.
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| 7. |
- Amloy, Supaluck, et al.
(author)
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Polarized emission from single GaN quantum dots grown by molecular beam epitaxy
- 2011
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In: AIP Conference Proceedings. - : AIP. - 1551-7616 .- 0094-243X. - 9780735410022 ; 1399, s. 541-542
-
Conference paper (peer-reviewed)abstract
- Polarization resolved microphotoluminescence measurements of single MBE-grown GaN/Al(Ga)N quantum dots (QDs) have been performed. The exciton and biexciton peaks with full width at half maximum as narrow as
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| 8. |
- Amloy, Supaluck, et al.
(author)
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Size dependent biexciton binding energies in GaN quantum dots
- 2011
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 99:25
-
Journal article (peer-reviewed)abstract
- Single GaN/Al(Ga)N quantum dots (QDs) have been investigated by means of microphotoluminescence. Emission spectra related to excitons and biexcitons have been identified by excitation power dependence and polarization resolved spectroscopy. All investigated dots exhibit a strong degree of linear polarization (similar to 90%). The biexciton binding energy scales with the dot size. However, both positive and negative binding energies are found for the studied QDs. These results imply that careful size control of III-Nitride QDs would enable the emission of correlated photons with identical frequencies from the cascade recombination of the biexciton, with potential applications in the area of quantum information processing.
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| 9. |
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| 10. |
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| 11. |
- Andersson, Thorvald, 1946, et al.
(author)
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Macroscopic defects in GaN/AlN multiple quantum well structures grown by MBE on GaN templates
- 2009
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In: Microelectronics Journal. - : Elsevier BV. - 0026-2692. ; 40:2, s. 360-362
-
Journal article (peer-reviewed)abstract
- We have used MBE to grow in AlN/GaN superlattices, with different number of periods, on 2.5-mu m-thick MOVPE-GaN templates to study the development of defects such as surface deformation due to strain. After growth the samples were studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), XRD and Fourier transform infrared spectroscopy (FT-IR). The strain increased with the number of quantum wells (QWs) and eventually caused defects such as microcracks visible by optical microscopy at four or more QW periods. High-resolution TEM images showed shallow recessions on the surface (surface deformation) indicating formation of microcracks in the MQW region. The measured intersubband (IS) absorption linewidth from a four period structure was 97 meV, which is comparable with the spectrum from a 10 period structure at an absorption energy of similar to 700 meV. This indicates that the interface quality of the MQW is not substantially affected by the presence of cracks.
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| 12. |
- Andersson, Thorvald, 1946, et al.
(author)
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Preparation and characterization of the ITO surface and the Al/Alq3/ITO heterostructure for OLEDs
- 2007
-
In: Materials Science and Engineering B. ; 145, s. 48-56
-
Journal article (peer-reviewed)abstract
- We have made a detailed investigation of structure and chemical composition in thermally grown Al/Alq3/ITO layer structures intended for light emission. The different parts of the structure were studied by X-ray photoelectron spectroscopy and microscopical techniques. The indium tinoxide substrate surface consisted of grains 20–50 nm in diameter and about 5 nm in height, which also showed molecular sized sub-grain features. Due to the ambient the ITO surface was covered by a 1 nm thick hydrocarbon layer which serves as the actual surface on which an organic layer is deposited for device fabrication. A structural model for the indium tin oxide surface, on which the small molecules were deposited, was suggested. The substrate surface was treated to study the relation between the surface manipulation and the hole injection barrier. Such surface modification significantly improved the performance of a single layer Alq3 organic light emitting diode. Depth profiling of the complete structure, revealed that the aluminium contact mostly consisted of aluminium oxide with some intermixing of carbon. Further, variations of the atomic concentration of the elements In, Sn, C and O and a minor shift in their binding energies were measured. Both, position and shape of the oxygen and indium peaks were changed during argon ion sputtering. At the Alq3/ITO interface an indium–oxygen compound, different from that on the original surface, hadformed. Various effects of the compositional findings on the light emission are discussed.
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| 13. |
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| 14. |
- Andreasson, Måns, 1975, et al.
(author)
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Porphyrin doping of Alq3 for electroluminescence
- 2008
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In: Current Applied Physics. - 1567-1739. ; 8, s. 163-166
-
Journal article (peer-reviewed)abstract
- Organic light emitting devices based on tris(8-hydroxyquinoline)aluminium (Alq3) doped with two fluorescent porphyrin derivatives,5,15-diphenyl-2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrin and the corresponding zinc metalated one, were fabricated. As a consequence,the light emission changed, from standard green light from Alq3, to reddish and yellowish white respectively. The differentspectral content in the two cases indicates a possible route to a white light emitter, based on several dopants from the same family ofmolecules with different central atoms. The turn-on voltage of the devices was not increased by the doping.
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| 15. |
- Berland, Kristian, 1983, et al.
(author)
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Polarization-balanced design of heterostructures: Application to AlN/GaN double-barrier structures
- 2011
-
In: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 84:24
-
Journal article (peer-reviewed)abstract
- Inversion and depletion regions generally form at the interfaces between doped leads ( cladding layers) and the active region of polar heterostructures like AlN/GaN and other nitride compounds. The band bending in the depletion region sets up a barrier that may seriously impede perpendicular electronic transport. This may ruin the performance of devices such as quantum-cascade lasers and resonant-tunneling diodes. Here we introduce the concepts of polarization balance and polarization-balanced designs: A structure is polarization balanced when the applied bias match the voltage drop arising from spontaneous and piezeolectric fields. Devices designed to operate at this bias have polarization-balanced designs. These concepts offer a systematic approach to avoid the formation of depletion regions. As a test case, we consider the design of AlN/GaN double-barrier structures with Al((x) over tilde)Ga(1-(x) over tilde)N leads. To guide our efforts, we derive a simple relation between the intrinsic voltage drop arising from polar effects, average alloy composition of the active region, and the alloy concentration of the leads. Polarization-balanced designs secure good filling of the ground state for unbiased structures, while for biased structures with efficient emptying of the active region they remove the depletion barriers.
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| 16. |
- Berland, Kristian, 1983, et al.
(author)
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Temperature stability of intersubband transitions in AlN/GaN quantum wells
- 2010
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 97:4, s. 043507-
-
Journal article (peer-reviewed)abstract
- Temperature dependence of intersubband transitions in AlN/GaN multiple quantum wells grown with molecular beam epitaxy is investigated both by absorption studies at different temperatures and modeling of conduction-band electrons. For the absorption study, the sample is heated in increments up to 400 degrees C. The self-consistent Schroumldinger-Poisson modeling includes temperature effects of the band gap and the influence of thermal expansion on the piezoelectric field. We find that the intersubband absorption energy decreases only by similar to 6 meV at 400 degrees C relative to its room temperature value.
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| 17. |
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| 18. |
- Farivar, Rashid, 1982, et al.
(author)
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Initial boron growth on GaN and AlN surfaces by molecular beam epitaxy
- 2010
-
In: Physica Status Solidi (C) Current Topics in Solid State Physics. - : Wiley. - 1610-1642 .- 1862-6351. ; 7:1, s. 25-27
-
Conference paper (peer-reviewed)abstract
- Elemental boron was thermally deposited, using the MBEtechnique, on surfaces of AlN and GaN. To suppress boron clustering, nitrogen was supplied from an RF nitrogen plasma source. Reflection high energy electron diffraction was used to monitor the surface before and during the growth. On the GaN surface, low concentrations of boron (̃0.1 ML) resulted in additional 6-fold highly streaky reflection rods indicating a reconstructed GaN(0001) surface. By increasing the boron concentration to ̃0.5 ML, however, the growth resulted in the formation of 3D islands as observed by spots in the RHEED pattern. Islands were also observed by atomic force microscopy and scanning electron microscopy. The AlN surface produced surface morphological features already for the lowest boron concentration, i.e. ̃0.1 ML coverage. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.
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| 19. |
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| 20. |
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| 21. |
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| 22. |
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| 23. |
- Ive, Tommy, 1968, et al.
(author)
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Design and Fabrication of AlN/GaN Heterostructures for Intersubband Technology
- 2012
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In: Japanese Journal of Applied Physics. - 1347-4065 .- 0021-4922. ; 51:1, s. Article Number: 01AG07 -
-
Journal article (peer-reviewed)abstract
- We have used models based on the effective-mass approximation and Schrodinger-Poisson to design AlN/GaN multiple quantum well structures for intersubband transitions between two or three energy levels. The structures were realized by molecular beam epitaxy and the surface morphology and structural quality were investigated. We also investigated GaN waveguides that were fabricated using standard cleanroom techniques. Our work is focused on the various challenges associated to the fabrication of quantum cascade lasers based on group III-nitrides. These challenges are discussed in the light of our results.
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| 24. |
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| 25. |
- Lee, C. B., et al.
(author)
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Investigation of charge carrier mobility in 5,6,11,12-tetraphenylnapthacene (rubrene) and coumarin 6 doped Alq(3) films
- 2007
-
In: Solid State Communications. - : Elsevier BV. - 0038-1098. ; 142:4, s. 206-211
-
Journal article (peer-reviewed)abstract
- The doping effect on charge carrier mobility in tris (8-hydroxyquinolinato) aluminum (Alq(3)) was studied by time-of-flight (TOF) measurements. The polar dopant, coumarin 6 (C-6) and extensive pi conjugated dopant, 5,6,11,12-tetraphenylnaphthacene (rubrene) were used for this study. The co-doped of rubrene (Rb) with C-6 into Alq3 improved the carrier mobility compared to the single doped Alq3:C-6 film. The carrier mobility in single doped Alq3:C-6 film did not follow the linear relationship of Poole-Frenkel (PF) model with applied electric field. The mobility was in agreement with the PF model at two different ranges of electric fields (F) separated by a critical field root Fc approximate to 373 (V/cm)(1/2). The mobility in co-doped Alq(3):(Rb:C-6) film followed the linear relationship with the PF model. The energetic disorder was found as similar to 0.32 eV in co-doped films. It was similar to 0.55 and similar to 0.27 eV before and after the critical field in Alq3:C-6 film. The values of positional disorders in co-doped films were estimated as similar to 1.8 and it was similar to 2 in Alq(3):C-6 film at root F
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| 26. |
- Liu, Xinju, 1979, et al.
(author)
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Aluminum monolayers on Si (1 1 1) for MBE-growth of GaN
- 2007
-
In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 300:1, s. 114-117
-
Journal article (peer-reviewed)abstract
- Up to 10 monolayers of Al were deposited on Si (1 1 1) surfaces at low (450 °C) and high (640 °C) temperatures before the molecular beam epitaxy growth of GaN. The influence of the Al monolayers on the overall GaN epitaxial layers was investigated by reflection high-energy electron diffraction, atomic force microscopy, high-resolution X-ray diffraction and transmission electron microscopy. At high-temperature deposition, 1.3 monolayer Al gave the smoothest GaN surface and best crystalline quality. At the low temperature, only 0.8 ML provided the same GaN quality.
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| 27. |
- Liu, Xinju, 1979, et al.
(author)
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Cracks in GaN/AlN multiple quantum well structures grown by MBE
- 2008
-
In: Journal of Physics, Conference Series. - : Institute of Physics (IOP). - 1742-6588 .- 1742-6596. ; 100, s. 042026-
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Journal article (peer-reviewed)abstract
- Due to the large lattice constant mismatch and thermal expansion coefficient difference between GaN and AlN, large strain is generated inside the GaN/AlN multiple quantum wells, which causes cracks in the structure. We investigated such cracks by optical microscopy and AFM. The crack density was studied with buffer and cap layer thickness, the number of quantum well periods, and the temperature reduction rate after growth as parameters. It was found that the crack density increased exponentially, with the number of periods above 4. Besides, a very thin, 100 nm, GaN buffer layer and similar to 300 nm GaN cap layer greatly reduced the crack density.
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| 28. |
- Liu, Xinju, 1979, et al.
(author)
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Growth of GaN and GaN/AlN multiple quantum wells on sapphire, Si and GaN template by molecular beam epiotaxy
- 2007
-
In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 300:1, s. 79-82
-
Journal article (peer-reviewed)abstract
- GaN layers of 280 nm thick were grown on sapphire, silicon (1 1 1) and GaN template by plasma assisted molecular beam epitaxy. From atomic force microscopy and high-resolution X-ray diffraction, it was found that GaN grown on sapphire and template gave smooth surface (RMS less then 0.5 nm) and very high crystalline quality (FWHM of (0 0 0 2) scan on sapphire only 48 arcsec). However, GaN growth on Si (1 1 1) provided rough surface and poor crystalline quality. The GaN/AlN multiple quantum well structures were grown on sapphire and template. Intersubband absorption spectra from Fourier transform infrared spectroscopy indicated that layers on GaN templates had better performances than on sapphire substrates.
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| 29. |
- Liu, Xinju, 1979, et al.
(author)
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Intersubband absorption at 1.5-3.5 µm in GaN/AlN multiple quantum wells grown by molecular beam epitaxy on sapphire
- 2007
-
In: Physica status solidi. - : Wiley. - 0370-1972 .- 1521-3951. ; 244:8, s. 2892-2905
-
Journal article (peer-reviewed)abstract
- Ten and twenty period multiple quantum well structures with 1.5-5.4 nm GaN wells and 1.2-5.1 nm AlN barriers were grown on sapphire by molecular beam epitaxy. Layer thicknesses were determined by X-ray diffraction measurements and simulations. Reciprocal space mapping showed that the relaxation of the quantum well layers was independent of the buffer layer thickness. Intersubband absorption was observed by Fourier transform infrared spectroscopy at λ ∼ 1.5-3.5 μm. Monolayer fluctuations in the quantum well width induced multiple peaks in spectra, which were well fitted to Lorentzian peaks of only 57 meV linewidth. Samples were very homogeneous as the absorption peak energy varied less than 1% along ∼4 cm on 2 inch wafers. The intersubband transition energies were calculated considering the conduction-band nonparabolicity, built-in fields, strain, and many-body effects. The calculation and comparison to the fitted Lorentzian peak energies indicated a moderate blueshift due to many-body effects. It was shown by both experiments and calculations that the AlN barrier width affects the intersubband transition energy.
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| 30. |
- Liu, Xinju, 1979, et al.
(author)
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Investigation of intersubband absorption of GaN/AlN multiple quantum wells grown on different substrates by molecular beam epitaxy
- 2007
-
In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 301:SPEC. ISS., s. 301-302
-
Journal article (peer-reviewed)abstract
- Ten period GaN/AlN multiple quantum well (MQW) structures were grown by plasma-assisted molecular beam epitaxy (MBE) on sapphire substrates and metal-organic vapour-phase epitaxy (MOVPE)-grown GaN templates. Samples were investigated by high-resolution X-ray diffraction (HR-XRD) and Fourier transform infrared (FT-IR) spectroscopy. Intersubband (IS) absorbances and FWHM of IS absorption peaks indicated that samples grown on the GaN templates had better characteristics, resulting in a FWHM as low as 93 meV at a peak energy of 700 meV.
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| 31. |
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| 32. |
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| 33. |
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| 34. |
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| 35. |
- Rorsman, Niklas, 1964, et al.
(author)
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Characterization of InAlAs/InGaAs HFETs with high indium content in the channel grown on GaAs substrate
- 1993
-
In: 23rd European Solid State Device Research Conference, ESSDERC 1993. - 1930-8876. - 9782863321355 ; , s. 765-768
-
Conference paper (peer-reviewed)abstract
- InAlAs/InGaAs HFETs having very high indium content (80 and 100%) in the channel have been fabricated on GaAs and electrically characterized. The extrinsic transconductance were 310 mS/mm (560 mS/mm at 77 K), and the saturation current were 700 mA/mm (600 mA/mm at 77 K) for an InAs channel. The value of fT and fmaxfor this device were measured to be 80 GHz and 50 GHz, respectively. The In0.8Ga 0.2As channel material had extrinsic transconductance of 320 mS/mm (470 mS/mm at 77 K), and the saturation current were 520 mA/mm (440 mA/mm at 77K). The value of fT and fmaxfor this device were measured to be 80 GHz and 50 GHz, respectively
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| 36. |
- Rouhani-Kalleh, A., et al.
(author)
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Resistance in sub-m size GaAs lines
- 1987
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In: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 3:4, s. 417-419
-
Journal article (peer-reviewed)abstract
- The electrical resistance in GaAs submicron mesa lines has been studied as a function of the line width. Using molecular beam epitaxy two types of conducting layers were made: an n+-layer and a two-dimensional electron gas confined to an (AlGa)As/GaAs heterostructure. Processing of the lines was made by photolithography, electron beam lithography and ion etching. Resistance data at 77 K and 300 K are discussed for line widths in the interval 0.2 to 5 m. A size dependent conduction was found and interpreted in terms of geometry induced limitation of the effective conducting path
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| 37. |
- Stattin, Martin, 1983, et al.
(author)
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Waveguides for nitride based quantum cascade lasers
- 2011
-
In: Physica Status Solidi (C) Current Topics in Solid State Physics. - : Wiley. - 1610-1642 .- 1862-6351. ; 8:7-8, s. 2357-2359
-
Journal article (peer-reviewed)abstract
- Waveguide designs for AlGaN-based near-infrared quantum cascade lasers are investigated using a finite-difference method mode solver. Because of the negligibly small refractive index difference between the AlN/GaN/AlGaN gain region and the surrounding AlGaN current injection and extraction layers, a low refractive index substrate (sapphire) and a low refractive index dielectric (SiO2) are used for vertical confinement of the optical field. A ridge waveguide with an off-center contact metallization is used for lateral confinement. The off-center contact allows for the propagation of a TM mode with low metal induced loss and sufficient optical confinement in the gain region. A viable waveguide design with a metal-induced loss of 6.1 cm-1 and a confinement factor of 0.52 is demonstrated.
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| 38. |
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| 39. |
- Uddin, A., et al.
(author)
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Initial rise of transient electroluminescence in doped Alq(3) films
- 2010
-
In: Physica Status Solidi (A) Applications and Materials Science. - : Wiley. - 1862-6319 .- 1862-6300. ; 207:10, s. 2334-2338
-
Journal article (peer-reviewed)abstract
- The doping effect on initial rise of transient electroluminescence (EL) in organic light emitting diodes (OLEDs) is investigated. The dopants red light emitter 5,6,11,12-tetraphenylnaphthacene (Rb) and 4-(diacynomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyan (DCM), and yellow light emitter 3-(2'-benzothiazolyl)-7-diethylaminocoumarin (C-6) were used in green light emitter tris-(8-hydroxyquinoline) aluminum (Alq(3)) film with various concentrations from 0.5 to 24wt%. The increase of EL delay time and the slower rise of EL saturation were observed with doping concentrations. The values of EL delay time was found from 0.78 to 1.86 mu s in doped OLED compared to 0.74 mu s in pure Alq(3) device. The EL saturation time was found from 1.2 to 2.8 mu s for different doping concentration. We have also estimated the carrier mobility from the transient EL measurements. The charge-carrier mobility was found as 0.5-1.2 x 10(-5) cm(2) V-1 s(-1) in doped Alq(3) films.
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| 40. |
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| 41. |
- Zsebök, Otto, 1965, et al.
(author)
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Morphology of InGaAs/GaAs quantum wires prepared by highly controlled deep-etching techniques
- 2001
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In: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 12, s. 32-7
-
Journal article (peer-reviewed)abstract
- Different types of InGaAs/GaAs deep-etched quantum wire (QWI) structure were successfully fabricated by high-energy electron beam lithography on GaAs(100) surfaces. A selective wet-chemical-etching technique, preceded by chemically assisted ion-beam etching, reduced the controlled lateral dimensions of the wires to ~10 nm due to strong under-etching. Various types of wire in the [011] and [011] crystallographic directions were prepared by the combined etching method. The side-walls of the wires were defined by the selectively etched low index crystallographic planes. A molecular-beam-epitaxy-grown graded InGaAs/GaAs quantum well was realized at the narrow `neck' region of the wires, thus providing the strongest possible lateral confinement of the QWI structure. Consequently, similarly to the selective growth of self-narrowing ridge structures, selective wet-chemical etching induced a controlled self-narrowing of the wire structures. Scanning electron microscopy images of the QWI nanostructures showed smooth side-walls defined by the crystallographic planes. Low-excitation photoluminescence spectroscopy of the structures revealed extremely high quantum efficiency and a size-dependent blue shift as a result of the strong lateral confinement
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