| 1. |
- Zhao, QX, et al.
(författare)
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Effect of growth temperature and post-growth thermal annealing on carrier localization and deep level emissions in GaNAs/GaAs quantum well structures
- 2005
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Ingår i: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 86:12
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Tidskriftsartikel (refereegranskat)abstract
- We report results from investigation of the optical properties of GaNAs/GaAs quantum well structures. The structures were grown by molecular-beam epitaxy at different temperatures, and subsequently postgrowth thermal treatments at different temperature were performed. The results show that the carrier localization is smaller in a structure grown at a temperature of 580 degrees C in comparison with a structure grown at 450 degrees C. Both structures also show a broaden deep level emission band. Furthermore, the deep level emission band and the carrier localization effect can be removed by thermal annealing at 650 degrees C in the structure grown at 450 degrees C. The structure quality and radiative recombination efficiency are significantly improved after annealing. However, annealing under the same condition has a negligible effect on the structure grown at 580 degrees C. (C) 2005 American Institute of Physics.
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| 2. |
- Zhao, QX, et al.
(författare)
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Effects of nitrogen incorporation on the properties of GaInNAs/GaAs quantum well structures
- 2005
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Ingår i: Journal of Applied Physics. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 97:7
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Tidskriftsartikel (refereegranskat)abstract
- We report results from theoretical and experimental investigations of GaInNAs/GaAs quantum well structures. Optical transition energies for samples with different In and N concentrations were determined by photoluminescence measurements. The results show that the reduction of the ground-state transition energy by the introduction of N decreases with increasing In concentration. The experimental data are compared with calculations using the effective-mass approximation. Modifications of the band-gap energy due to N incorporation were accounted for using the two-level repulsion model. Proper effective-mass and band offset values, based on recent experimental work, were used. Calculated and measured transition energies show good agreement. The critical thickness, lattice constant, strain, and optical transition energies are discussed for GaInNAs/GaAs quantum well structures tuned for emission at 1.3 and 1.55 mu m, in particular. Such a simple model, within the effective-mass approximation, is a very useful guide for device design. (C) 2005 American Institute of Physics.
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| 3. |
- Zhao, Qingxiang, 1962, et al.
(författare)
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Nitrogen incorporation in GaNas layers grown by molecular beam epitaxy
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:3, s. 31907-1-31907-3
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Tidskriftsartikel (refereegranskat)abstract
- GaNAs/GaAs quantum wells with high N concentrations, grown by molecular beam epitaxy, have been investigated by secondary-ion mass spectrometry (SIMS), high resolution x-ray diffraction (XRD), and photoluminescence (PL) measurements. The substitutional N concentration in an 18 nm thick strained GaNAs layer varies from 1.4% to 5.9% when the growth rate is reduced from 1 to 0.2 μm/h. By further reducing the growth rate, more N can be incorporated but relaxation occurs. Both the total N concentration, deduced from SIMS measurements, and the substitutional N concentration, deduced from XRD measurements, increase with reduced growth rate. By comparing the SIMS and XRD results, we found that a large amount of N was not in substitutional position when the substitutional N concentration is high (≫4%). The experimental results also show that there is no detectable change of total and substitutional N concentrations, within the instrument resolutions, after rapid thermal annealing at 700 °C for 30 s. However, PL measurements show a strong blueshift of the emission wavelength after annealing and the PL intensity increases by more than one order of magnitude.
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| 4. |
- Zhao, QX, et al.
(författare)
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Radiative recombination of localized excitons and mobility edge excitons in GaInNAs/GaAs quantum wells with strong carrier localization
- 2005
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Ingår i: Physics Letters A. - : Elsevier Science B.V., Amsterdam.. - 0375-9601 .- 1873-2429. ; 341:04-Jan, s. 297-302
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Tidskriftsartikel (refereegranskat)abstract
- The radiative recombination in InxGa1-xN0.01As0.99/GaAs quantum well structures exhibiting strong carrier localization was investigated by optical spectroscopy. For In-concentration from 0 to 30%, the results indicate that the degree of carrier localization decreases with increasing In-concentration. At temperatures below 100 K, the mobility edge excitons as well as localized excitons are identified and their transitions energies strongly depend on the excitation intensity. At elevated temperatures the localized excitons become quenched. The temperature dependence of the photoluminescence emission energy shows different behaviors at different excitation intensities.
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| 5. |
- Bengtsson, Magnus, et al.
(författare)
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Fluorescence lidar imaging of fungal growth on high-voltage outdoor composite insulators
- 2005
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Ingår i: Optics and Lasers in Engineering. - : Elsevier BV. - 0143-8166 .- 1873-0302. ; 43:6, s. 624-632
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Tidskriftsartikel (refereegranskat)abstract
- Remote fluorescence imaging of fungal growth on polymeric high-voltage insulators was performed using a mobile lidar system with a laser wavelength of 355 nm. Insulator areas contaminated by fungal growth could be distinguished from clean surfaces and readily be imaged. The experiments were supported by detailed spectral studies performed in laboratory using a fibre-optic fluorosensor incorporating an optical multi-channel analyser system (OMA) and a nitrogen laser emitting radiation at 33 7 nm.
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| 6. |
- Fu, Ying, et al.
(författare)
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Energy band structure and spectral gain characteristics of dilute-nitride zinc blende InGaNAs quantum wells embedded in GaAs and GaNAs barriers
- 2006
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 100:7
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Tidskriftsartikel (refereegranskat)abstract
- The spectral gain characteristics of dilute-nitride zinc blende InxGa1-xNyAs1-y quantum wells embedded in GaNy1As1-y1 barriers have been investigated experimentally and theoretically. Two samples, both with the gain peak at 1300 nm, were studied for comparison. One has a high nitrogen concentration in the quantum well with the surrounding barriers being pure GaAs. The other has a lower and uniform nitrogen concentration in the quantum well and the barriers (GaNAs barriers). Measurements show the redshift of the gain peak induced by the incorporation of nitrogen and difference in the spectral gain characteristics. The energy band structures and spectral gain characteristics are analyzed theoretically using the standard eight-band k center dot p theory. It is shown that the introduction of nitrogen atoms in the GaAs barriers reduces the barrier height for the central quantum well so that the energy sublevels in the conduction band becomes condensed. The condensation of the conduction-band energy sublevels reduces the peak gain and makes the gain spectrum narrower, in agreement with measurements.
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| 7. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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Mg-doped Al0.85Ga0.15N layers grown by hot-wall MOCVD with low resistivity at room temperature
- 2010
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Ingår i: PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS. - : John Wiley and Sons, Ltd. - 1862-6254 .- 1862-6270. ; 4:11, s. 311-313
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Tidskriftsartikel (refereegranskat)abstract
- We report on the hot-wall MOCVD growth of Mg-doped AlxGa1-xN layers with an Al content as high as x similar to 0.85. After subjecting the layers to post-growth in-situ annealing in nitrogen in the growth reactor, a room temperature resistivity of 7 k Omega cm was obtained indicating an enhanced p-type conductivity compared to published data for AlxGa1-xN layers with a lower Al content of x similar to 0.70 and a room temperature resistivity of about 10 k Omega cm. It is believed that the enhanced p-type conductivity is a result of reduced compensation by native defects through growth conditions enabled by the distinct hot-wall MOCVD system.
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| 8. |
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| 9. |
- Lindberg, Hans, 1977, et al.
(författare)
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High-power optically pumped 1550-nm VECSEL with a bonded silicon heat spreader
- 2004
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Ingår i: IEEE Photonics Technology Letters. - 1041-1135 .- 1941-0174. ; 16:5, s. 1233-1235
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Tidskriftsartikel (refereegranskat)abstract
- We present an optically pumped 1550-nm vertical-external-cavity surface-emitting laser with improved output power and operating temperature using a bonded heat spreader. The laser comprises an InGaAsP-based gain element, with a resonant periodic gain structure on top of a distributed Bragg reflector, and a high reflectivity spherical mirror as the external reflector. Heat transport is enhanced by a Si heat spreader bonded to the InGaAsP surface by liquid capillary bonding. Optical pumping is achieved using a 1250-nm fiber Raman laser. A maximum continuous output power of 250 mW was obtained under multitransverse mode operation at 240 K. Under operation in the fundamental near-Gaussian mode, we obtained a maximum power of 230 mW with a beam quality factor (M-2) of 1.22. At room temperature, the output power was limited to 12 mW.
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| 10. |
- Lindberg, Hans, 1977, et al.
(författare)
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InP-based optically pumped VECSEL operating CW at 1550 nm
- 2004
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Ingår i: IEEE Photonics Technology Letters. - 1041-1135 .- 1941-0174. ; 16:2, s. 362-364
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Tidskriftsartikel (refereegranskat)abstract
- We present a vertical external-cavity surface-emitting laser operating at 1550 run. The laser comprises an InGaAsP-based gain element, with a resonant periodic gain structure on top of a distributed Bragg reflector, and a high reflectivity spherical mirror as the external reflector. Optical pumping is achieved using a 1250-nm fiber Raman laser. A maximum continuous output power of 70 mW was obtained under multitransverse mode operation at 233 K. Under single-mode operation, we obtained a maximum power of 60 mW with a beam quality factor M-2 less than 1.1.
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