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| 2. |
- Aggerstam, Thomas, et al.
(författare)
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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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Ingår i: Quantum Sensing and Nanophotonic Devices IV. - : SPIE. - 9780819465924 ; 6479, s. 64791E-
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Konferensbidrag (refereegranskat)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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| 4. |
- Bäckstrand, Gunnar, et al.
(författare)
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The impact of information presentation on work environment and product quality : a case study
- 2008
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Ingår i: Proceedings of the 40th annual Nordic Ergonomic Society Conference. - Reykjavik : NES.
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Konferensbidrag (refereegranskat)abstract
- In manufacturing, it is vital that production personnel have the right information at the right time and place. The main purpose of information delivered to a workplace is to support the worker in a way that contributes to the quality of the product as well as productivity. However, when information processing becomes a large part of the workload, the time for core workplace activities is reduced. A study was conducted at a heavy diesel engine assembly line with the aim of finding how the assembly personnel interact with the information presented to them in their work context and how this affected quality and productivity. The study focused on four assembly stations and involved 70 assembly workers over a period of ten days and nights during which 2600 standard and customised variant engines were assembled. The main feature of the study was a change in the information system that reduced the amount of data and information provided, changed the location of the information, and modified the timing of information presentation. Results from the study show that the information presented at an assembly workstation influences the quality as well as the assembly process itself. The number of internal rejects decreased by 40% on two of the stations and on the other two stations no errors occurred during the study. This influence on the assembly process is of great importance from a quality perspective; by changing the information system and thereby the workers’ behaviour, the errors were reduced significantly. Whilst errors are few and detected internally, redressing these errors is a waste. Furthermore, an adequate information system boosts operator confidence and reduces cognitive stress levels. The information system used in this study was relatively simple (simpler than the regular system) and based on colour coded cards. Nevertheless, the impact was major and this indicates that when designing an information system for mass-customised assembly, a wide range of solutions needs to be considered. A study in final assembly of heavy trucks is planned for the future where the ultimate goal is to arrive at worker and task tailored presentation of information in customised assembly.
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| 5. |
- Case, Keith, et al.
(författare)
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An assembly line information system study
- 2008
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Ingår i: Advances in Manufacturing Technology – XXII. - Uxbridge : Brunel University. - 9781902316604 ; , s. 181-188
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Konferensbidrag (refereegranskat)
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| 6. |
- Liu, Xinju, 1979, et al.
(författare)
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Growth of GaN and GaN/AlN multiple quantum wells on sapphire, Si and GaN template by molecular beam epiotaxy
- 2007
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 300:1, s. 79-82
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Liu, Xinju, 1979, et al.
(författare)
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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
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Ingår i: Physica status solidi. - : Wiley. - 0370-1972 .- 1521-3951. ; 244:8, s. 2892-2905
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Liu, Xinju, 1979, et al.
(författare)
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Investigation of intersubband absorption of GaN/AlN multiple quantum wells grown on different substrates by molecular beam epitaxy
- 2007
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 301:SPEC. ISS., s. 301-302
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Tidskriftsartikel (refereegranskat)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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