| 1. |
- Niessen, Peter, et al.
(författare)
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Recent results from the amanda experiment
- 2003
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Ingår i: Proceedings of 38th Rencontres de Moriond on Electroweak Interactions and Unified Theories 15-22 Mar 2003. Les Arcs, France.
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Konferensbidrag (refereegranskat)abstract
- AMANDA (Antarctic Muon And Neutrino Detector Array) is a neutrino telescope built under the southern polar icecap and its scope is to explore the possibility to detect high energy cosmic neutrinos. This should generate insight into the powerful celestial objects where acceleration mechanisms can bring up to 10 20 eV. We describe the achievements and results from the AMANDA-B10 prototype and the preliminary results from the current AMANDA-II detector which show dramatic increase in sensitivity.
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| 2. |
- Barrios, C. A., et al.
(författare)
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GaAs/AlGaAs buried-heterostructure vertical-cavity surface-emitting laser with semi-insulating GalnP : Fe regrowth
- 2000
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Ingår i: Electronics Letters. - 0013-5194 .- 1350-911X. ; 36:18, s. 1542-1544
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Tidskriftsartikel (refereegranskat)abstract
- The authors report the first results of a GaAs/AlGaAs buried-heterostructure vertical-cavity surface-emitting laser (VCSEL) with semi-insulating Ga0.51In0.49P:Fe (SI-GaInP:Fe) as the burying layer. Regrowth of SI-GaInP:Fe around 15 mu m diameter and 8 mu m tall VCSEL mesas was carried out by hydride vapour phase epitaxy (HVPE). Under room temperature continuous wave (CW) operation. the device exhibited a threshold current of 3.5mA, a differential quantum efficency of 33% and a light output power of 4.2mW. CW operation at temperatures up to 97 degrees C is also demonstrated.
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| 3. |
- Carlsson, C., et al.
(författare)
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Performance characteristics of buried heterostructure VCSELs using semi-insulating GaInP : Fe regrowth
- 2001
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Ingår i: IEEE Journal of Quantum Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9197 .- 1558-1713. ; 37:7, s. 945-950
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated GaAs-AlGaAs buried heterostructure vertical cavity surface emitting lasers, emitting at 850 nm, using semi-insulating GaInP:Fe regrowth and investigated their static properties. Lasers of different size (10-21 mum) have threshold currents in the range 2.8-7.0 mA, and produce a maximum output power of 1.7-6.0 mW at room temperature. The variation of threshold current with device size shows that the leakage current at the regrowth interface accounts for a significant part of the injection current. In spite of this, a differential quantum efficiency in the range 20%-30% is obtained which indicates that the regrowth interface is smooth and does not introduce any significant scattering loss. Studies of the transverse mode properties suggest that the GaInP provides weak guiding, resulting in single mode operation up to an output power of 0.7 mW and a beam divergence of only 6 degrees for lasers as large as 10 mum.
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| 4. |
- Angulo Barrios, C., et al.
(författare)
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GaAs/AlGaAs buried-heterostructure laser diodes with semi-insulating GaInP:Fe regrowth
- 2001
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Ingår i: Lasers and Electro-Optics, 2001. CLEO/Pacific Rim 2001. The 4th Pacific Rim Conference on.
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Konferensbidrag (refereegranskat)abstract
- GaAs/AlGaAs buried-heterostructure in-plane lasers and vertical-cavity surface-emitting lasers using GaInP:Fe as the burying layer have been fabricated and investigated. Regrowth of GaInP:Fe around etched laser mesas was achieved by hydride vapor phase epitaxy. The lasers exhibit good performance under CW operation and show promising high-speed characteristics.
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| 5. |
- Barrios, C. A., et al.
(författare)
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Epitaxially regrown GaAs/AlGaAs laser mesas with semi-insulating GaInP : Fe and GaAs : Fe
- 2001
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Ingår i: Journal of Electronic Materials. - 0361-5235 .- 1543-186X. ; 30:8, s. 987-991
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Tidskriftsartikel (refereegranskat)abstract
- Selective regrowth of semi-insulating iron-doped Ga0.51In0.49P (SI-GaInP:Fe) and SI-GaAs:Fe around GaAs/AlGaAs mesas by hydride vapor phase epitaxy (HVPE) has been achieved. A HCl based in-situ cleaning procedure has been used to remove aluminum oxide from the etched walls of the mesas. Regrowth conducted without proper cleaning results in an irregular interface with voids. Regrowth morphology aspects are also presented. Our cleaning and regrowth methods have been used for fabricating GaAs/AlGaAs buried heterostructure in-plane lasers and vertical-cavity surface-emitting lasers.
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| 6. |
- Gaarder, A., et al.
(författare)
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Time-resolved micro-photoluminescence studies of deep level distribution in selectively regrown GaInP : Fe and GaAs : Fe
- 2002
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 17:2, s. 129-134
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Tidskriftsartikel (refereegranskat)abstract
- We apply time-resolved photoluminescence with 1-2 mum spatial resolution for the characterization of deep centre distributions in semi-insulating GaInP:Fe and GaAs:Fe epitaxial layers regrown by hydride vapour phase epitaxy around etched GaAs mesas and GaAs/AlGaAs quantum well laser structures. In InGaP, Fe ions act as the main carrier recombination centres, while in Fe-doped GaAs both the Fe ions and As antisite defects have to be considered. The distribution of Fe ions in InGaP was found to be rather uniform and close to the target value. For GaAs:Fe, the number of ionized Fe and EL2 centres showed a certain increase at the mesa interfaces. In both cases, the high trap concentration was maintained throughout the regrown layers indicating good semi-insulating material properties.
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| 7. |
- Gaarder, A., et al.
(författare)
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Time-resolved micro-photoluminescence studies of dopant distribution in selectively regrown GalnP : Fe around VCSELs
- 2002
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T101, s. 89-91
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Tidskriftsartikel (refereegranskat)abstract
- We apply time-resolved photoluminescence with 1.5 mum spatial resolution for characterization ofcarrier trap distribution in semi-insulating Ga0.51In0.49P:Fe layers regrown around GaAs/AlGaAs circular vertical cavity surface emitting laser mesas using hydride vapour phase epitaxy. The carrier trapping times are in the range from 10 to 15 ps and quite uniformly distributed throughout the burying GaInP:Fe layer, suggesting that the layer is semi-insulating everywhere. Simulations show that, in addition to the Fe dopants, the layer contains other, unintended carrier traps. The photoluminescence spectra reveal that the regrown GaInP:Fe material has several distinct regions with different band gaps. This is attributed to differences in the In/Ga composition and/or CuPt ordering of the GaInP.
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| 8. |
- Barrios, C. A., et al.
(författare)
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Analysis of leakage current in GaAs/AlGaAs buried-heterostructure lasers with a semi-insulating GaInP : Fe burying layer
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 92:5, s. 2506-2517
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Tidskriftsartikel (refereegranskat)abstract
- The leakage current in recently demonstrated GaAs/AlGaAs buried heterostructure (BH) lasers with a semi-insulating (SI) GaInP:Fe burying layer has been theoretically and experimentally analyzed. Calculated current-voltage characteristics of n-GaAs/SI-GaInP/n-GaAs and p-GaAs/SI-GaInP/p-GaAs planar configurations have been studied specially to assess the behavior of SI-GaInP:Fe under electron and hole injection. Two-dimensional potential profiles have been used to explain the leakage current mechanism in the SI-GaInP-buried lasers. Simulations reveal that the total leakage current decreases as the active trap concentration in the SI-GaInP:Fe burying layer is increased as expected, but the leakage current is strongly confined in the vicinity of the active region where the local leakage current density increases significantly as the trap density increases. It is found that the insertion of a n-GaInP hole blocking layer between the p-metal and the SI-GaInP layer decreases the total leakage current. Experimental light-current and current-voltage characteristics of fabricated lasers with and without an additional n-GaInP layer, and electroluminescence (EL) emitted from the burying GaInP:Fe layers corroborate qualitatively the simulations and demonstrate the benefits of using a n-GaInP layer for reducing leakage current in these type of lasers.
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| 9. |
- Barrios, C. A., et al.
(författare)
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GaAs/AlGaAs buried heterostructure laser by wet etching and semi-insulating GaInP : Fe regrowth
- 2000
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Ingår i: Electrochemical and solid-state letters. - 1099-0062 .- 1944-8775. ; 3:9, s. 439-441
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Tidskriftsartikel (refereegranskat)abstract
- Selective regrowth of semi-insulating Ga0.51In0.49P:Fe (SI-GaInP:Fe) by hydride vapor-phase epitaxy around Al-containing wet etched laser mesas is used for the first time to fabricate a GaAs/AlGaAs buried heterostructure laser emitting at 808 nm. The reverse and forward current-voltage characteristics measured at different temperatures up to 80 degrees C indicate no serious leakage current problems. The performance of the laser shows that the SI-GaInP: Fe burying layer fulfills its function as a current and optical confinement layer. The fabrication procedure and the laser characteristics are presented.
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| 10. |
- Douheret, O., et al.
(författare)
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Characterization of GaAs/AlGaAs laser mesas regrown with semi-insulating GaInP by scanning capacitance microscopy
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:6, s. 960-962
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Tidskriftsartikel (refereegranskat)abstract
- In this work, cross-sectional scanning capacitance microscopy (SCM) is used to investigate GaAs/AlGaAs buried heterostructure lasers. Laser mesas are buried with GaInP:Fe selectively regrown by hydride vapor phase epitaxy. It is shown that a complete 2D map of the electrical properties of device structure including, delineation of regrown interfaces and electrical nature of the regrown GaInP layer can be obtained. The behavior of the SCM signal with ac bias is used to verify the semi-insulating nature of the regrown layer at different locations of the sample. The measured SCM signal for the regrown GaInP:Fe layer is uniformly zero, indicating very low free carrier densities and confirming semi-insulating properties. This observation strongly suggests, in addition, uniform Fe incorporation in the regrown layers, close to and far away from the mesa. Finally, a nanoscale feature in the SCM contrast appearing as a bright (dark) spot in dC/dV mode (feedback bias mode) is observed at the mesa sidewall close to the interface between the regrown GaInP:Fe and the p-cladding layer. The origin of this contrast is discussed in terms of local band-bending effects and supported by 2D Poisson simulations of the device structure.
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| 11. |
- Fox, A, et al.
(författare)
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Increased levels of bacterial markers and CO2 in occupied school rooms
- 2003
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Ingår i: Journal of Environmental Monitoring. - : Royal Society of Chemistry (RSC). - 1464-0325 .- 1464-0333. ; 5:2, s. 246-252
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Tidskriftsartikel (refereegranskat)abstract
- Our group previously demonstrated that carbon dioxide (CO2) levels in heavily occupied schools correlate with the levels of airborne bacterial markers. Since CO2 is derived from the room occupants, it was hypothesized that in schools, bacterial markers may be primarily increased in indoor air because of the presence of children: directly from skin microflora or indirectly, by stirring up dust from carpets and other sources. The purpose of this project was to test the hypothesis. Muramic acid (Mur) is found in almost all bacteria whereas 3-hydroxy fatty acids (3-OH FAs) are found only in Gram-negative bacteria. Thus Mur and 3-OH FA serve as markers to assess bacterial levels in indoor air (pmol m-3). In our previous school studies, airborne dust was collected only from occupied rooms. However, in the present study, additional dust samples were collected from the same rooms each weekend when unoccupied. Samples were also collected from outside air. The levels of dust, Mur and Cu-10:0, C-12:0, C-14:0, and C-16:0 3-OH FAs were each much higher (range 5 50 fod) in occupied rooms than in unoccupied school rooms. Levels in outdoor air were much lower than that of indoor air from occupied classrooms and higher than the levels in the same rooms when unoccupied. The mean CO2 concentrations were around 420 parts per million (ppm) in unoccupied rooms and outside air: and they ranged from 1017 to 1736 ppm in occupied rooms, regularly exceeding 800-1000 ppm, which are the maximum levels indicative of adequate indoor ventilation. This indicates that the children were responsible for the increased levels of bacterial markers. However, the concentration of Mur in dust was also 6 fold higher in occupied rooms (116.5 versus 18.2 pmole mg(-1)). This further suggests that airborne dust present in occupied and unoccupied rooms is quite distinct. In conclusion in unoccupied rooms, the dust was of environmental origin but the children were the primary source in occupied rooms.
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| 12. |
- Gaarder, A., et al.
(författare)
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Dopant distribution in selectively regrown InP : Fe studied by time-resolved photoluminescence
- 2001
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 226:4, s. 451-457
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Tidskriftsartikel (refereegranskat)abstract
- We apply time-resolved photoluminescence with 1 mum spatial resolution for the characterization of iron distribution in semi-insulating InP:Fe epitaxial layers regrown by hydride vapor-phase epitaxy around etched mesas. The InP:Fe regrowth was carried out on InP:S mesas etched both along the [110] and [110] crystallographic directions, as well as on InP/InGaAsP in-plane lasers. In all cases, the Fe concentration was found to be close to the target values and showed little variation along the regrown layers.
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| 13. |
- Kamp, M., et al.
(författare)
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Ultrashort InGaAsP/InP lasers with deeply etched Bragg mirrors
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:26, s. 4074-4075
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated short cavity lasers with deeply etched Bragg mirrors based on 1.55 mum emitting InGaAsP/InP laser structures. Continuous-wave operation has been obtained for devices with a length of 40 mum, showing threshold currents of 12 mA. The dynamic properties of the lasers were studied by measurements of the relative intensity noise (RIN). A maximum modulation frequency of 8.4 GHz was extracted from the RIN data.
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| 14. |
- Soderstrom, D., et al.
(författare)
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Dopant diffusion and current-voltage studies on epitaxial InP codoped with Ru and Fe
- 2001
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Ingår i: Journal of Electronic Materials. - 0361-5235 .- 1543-186X. ; 30:8, s. 972-976
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Tidskriftsartikel (refereegranskat)abstract
- Semi-insulating Fe and Ru codoped InP epitaxial layers grown by low-pressure hydride vapor phase epitaxy have been investigated. InP:Ru and InP:Fe,Ru layers were grown on p-InP:Zn and n-InP:S substrates, in order to study dopant diffusion and electrical characteristics. Dopant diffusion profiles of Ru, Fe and Zn were measured by secondary ion mass spectroscopy. A small but noteworthy diffusion front is observed when InP:Ru is adjacent to InP:Zn, but not when adjacent to n-InP. For InP:Fe codoped with Ru a pronounced interdiffusion of Fe and Zn is observed for Ru concentrations less than 2 X 10(17) cm(-3), but, for a higher Ru concentration the interdiffusion is clearly suppressed. Moreover, when InP is codoped with Fe and Ru, the small diffusion tail of Ru in InP:Zn vanishes. Unlike InP:Fe, resistivities above 1 X 10(8) Ohm cm are measured for both electron and hole-current injection in InP:Fe,Ru.
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| 15. |
- Soderstrom, D., et al.
(författare)
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Electrical characterization of ruthenium-doped InP grown by low pressure hydride vapor phase epitaxy
- 2001
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Ingår i: Electrochemical and solid-state letters. - 1099-0062 .- 1944-8775. ; 4:6, s. G53-G55
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial layers of ruthenium-doped InP grown by low-pressure hydride vapor phase epitaxy have been studied. Current voltage measurements were conducted at temperatures between 20 and 200 degreesC for samples doped with Ru in the range 1 x 10(17) to 5 X 10(17) cm(-3). In this doping range, the specific resistivity of n(+)/InP:Ru/n(+) structures accommodating electron injection is less than or equal to1 x 10(4) Ohm cm and that of p(+)/InP:Ru/p(+) structures accommodating hole injection is as high as 3 x 10(10) Ohm cm. The reason for such a huge difference in the resistivity of these structures is attributed to a low activation of deep Ru acceptors, thus rather giving rise to an n(-) layer than a semi-insulating layer, as supported by our theoretical simulation. Analysis of the Arrhenius plots constructed from the temperature-dependent I-V curves yield an average activation energy of Ru with reference to the conduction band equal to 0.44 and 0.52 eV under electron and hole injection, respectively.
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| 16. |
- Soderstrom, D., et al.
(författare)
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Studies on ruthenium-doped InP growth by low-pressure hydride vapor-phase epitaxy
- 2001
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 148:7, s. G375-G378
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Tidskriftsartikel (refereegranskat)abstract
- Ruthenium-doped InP (InP:Ru) has been grown by low-pressure hydride vapor-phase epitaxy (LP-HVPE) using bis(eta (5)-2,4-dimethylpentadienyl)ruthenium(II) as precursor. Ruthenium concentrations in the range 2 x 10(15) to 2 x 10(18) cm(-3) have been achieved. The Ru incorporation has been studied in terms of incorporation flux, and it is shown that the growth rate limits: the incorporation rate. From current-voltage measurements on n-InP/InP:Ru/n-InP and p-InP/InP:Ru/p-InP structures, resistivities greater than 10(3) Omega cm and greater than 10(10) Omega cm have been obtained, respectively.
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| 17. |
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| 18. |
- Sun, Y. T., et al.
(författare)
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Selective growth of InP on focused-ion-beam-modified GaAs surface by hydride vapor phase epitaxy
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 79:12, s. 1885-1887
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Tidskriftsartikel (refereegranskat)abstract
- The growth of InP islands on a planar focused-ion-beam (FIB)-modified (001) GaAs substrate was investigated in a hydride vapor phase epitaxy system. InP grew selectively on the FIB-implanted lines, forming continuous stripes, whereas isolated islands were observed outside the implanted area. The impact of the III/V ratio, crystallographic orientation of implanted lines, and implantation dose was explored. The choice of suitable growth conditions makes it possible to obtain continuous InP wires aligned in all possible directions. The results of this work could be used for the fabrication of future optoelectronic integrated circuits, which would include nanoscale structures, e.g., quantum-wire optical devices with GaAs electronic circuits.
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