| 1. |
- Chen, I. Ju, et al.
(författare)
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Hot-Carrier Extraction in Nanowire-Nanoantenna Photovoltaic Devices
- 2020
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 20:6, s. 4064-4072
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Tidskriftsartikel (refereegranskat)abstract
- Nanowires bring new possibilities to the field of hot-carrier photovoltaics by providing flexibility in combining materials for band engineering and using nanophotonic effects to control light absorption. Previously, an open-circuit voltage beyond the Shockley-Queisser limit was demonstrated in hot-carrier devices based on InAs-InP-InAs nanowire heterostructures. However, in these first experiments, the location of light absorption, and therefore the precise mechanism of hot-carrier extraction, was uncontrolled. In this Letter, we combine plasmonic nanoantennas with InAs-InP-InAs nanowire devices to enhance light absorption within a subwavelength region near an InP energy barrier that serves as an energy filter. From photon-energy- and irradiance-dependent photocurrent and photovoltage measurements, we find that photocurrent generation is dominated by internal photoemission of nonthermalized hot electrons when the photoexcited electron energy is above the barrier and by photothermionic emission when the energy is below the barrier. We estimate that an internal quantum efficiency up to 0.5-1.2% is achieved. Insights from this study provide guidelines to improve internal quantum efficiencies based on nanowire heterostructures.
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| 2. |
- Deppert, Knut, et al.
(författare)
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Aerotaxy: High throughput gas-phase epitaxy of nanostructures
- 2020
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Konferensbidrag (refereegranskat)abstract
- Aerotaxy is an aerosol-based growth method for semiconductors and we present in detail how aerotaxy can be used to grow nanowires continuously with controlled nanoscale dimensions, with a high degree of crystallinity and remarkable throughput, including process details and our current understading of the growth processes. Catalytic size-selected Au aerosol particles travel through a heated flow-through reactor and mix with III–V precursor flux, which nucleates the growth of nanowires. We demonstrate that the method allows sensitive and reproducible control of the nanowire dimensions and shape. The reported continuous and potentially high-throughput method is expected to substantially reduce the cost of producing high-quality nanowires and may enable the low-cost fabrication of nanowire-based devices on an industrial scale.
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| 3. |
- Johansson, Jonas, et al.
(författare)
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Calculation of hole concentrations in Zn doped GaAs nanowires
- 2020
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 10:12
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Tidskriftsartikel (refereegranskat)abstract
- We have previously demonstrated that we can grow p-type GaAs nanowires using Zn doping during gold catalyzed growth with aerotaxy. In this investigation, we show how to calculate the hole concentrations in such nanowires. We base the calculations on the Zhang–Northrup defect formation energy. Using density functional theory, we calculate the energy of the defect, a Zn atom on a Ga site, using a supercell approach. The chemical potentials of Zn and Ga in the liquid catalyst particle are calculated from a thermodynamically assessed database including Au, Zn, Ga, and As. These quantities together with the chemical potential of the carriers enable us to calculate the hole concentration in the nanowires self-consistently. We validate our theoretical results against aerotaxy grown GaAs nanowires where we have varied the hole concentration by varying the Zn/Ga ratio in the aerotaxy growth.
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| 4. |
- Junesand, Carl, et al.
(författare)
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Effect of the Surface Morphology of Seed and Mask Layers on InP Grown on Si by Epitaxial Lateral Overgrowth
- 2012
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Ingår i: Journal of Electronic Materials. - : Springer Verlag (Germany) / Institute of Electrical and Electronics Engineers (IEEE). - 0361-5235 .- 1543-186X. ; 41:9, s. 2345-2349
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Tidskriftsartikel (refereegranskat)abstract
- Heteroepitaxy of InP on Si by epitaxial lateral overgrowth (ELOG) using a thin seed layer of InP as starting material is investigated, with special attention given to the effect of the surface morphology of the seed and the mask layers on the quality of the ELOG layers. Chemical mechanical polishing (CMP) has been used to improve the morphological and optical quality of InP grown by hydride vapor-phase epitaxy (HVPE) using ELOG. Two approaches have been investigated: polishing the InP seed layer on Si before depositing the SiO2 mask and polishing the SiO2 mask after its deposition on the unprocessed seed layer. For polishing the InP (seed)/Si, a two-step process with an aluminum oxide- and sodium hypochlorite-containing slurry as well as a slurry based on sodium hypochlorite mixed with citric acid was used. For SiO2 mask polishing, a slurry with colloidal silica as an abrasive was employed. In both cases, the SiO2 mask was patterned with double line openings and ELOG carried out in an HVPE reactor. Morphology and crystal quality of the resulting ELOG layers were studied with atomic force microscopy (AFM) and room-temperature panchromatic cathodoluminescence (PC-CL) in situ in a scanning electron microscope (SEM), respectively. The results show that, whereas both polishing approaches result in an ELOG InP layer with good morphology, its surface roughness is lower when the InP (seed)/Si is subjected to CMP prior to deposition of the SiO2 mask, than when only the SiO2 mask is polished. This approach also leads to a decrease in the number of defects generated during coalescence of the ELOG layers.
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| 5. |
- Junesand, Carl, et al.
(författare)
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Heteroepitaxial Growth of Indium Phosphide from Nano-openings Made by Masking on a Si(001) Wafer
- 2010
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Ingår i: 2010 22ND INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS (IPRM). - 9781424459209
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Konferensbidrag (refereegranskat)abstract
- We investigate nano-eptiaxial lateral overgrowth (NELOG) of InP from the nano-sized openings on a seed layer on the silicon wafer, by Hydride Vapor Phase Epitaxy (HVPE). The grown layers were analyzed by cathodoluminescence (CL) in situ a scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results from InP: S growth shows that the boundary plane of the grown layer has a major impact on the luminescence, indicating preferential orientation-dependent doping. Moreover, although there is clear evidence that most of the threading dislocations originating in the InP seed layer/Si interface are blocked by the mask, it appears that new dislocations are generated. Some of these dislocations are bounding planar defects such as stacking faults, possibly generated by unevenness in the mask. Finally, patterns where coalescence takes place at higher thickness seem to result in a rougher surface.
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| 6. |
- Junesand, Carl, et al.
(författare)
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Heteroepitaxial Indium Phosphide on Silicon
- 2010
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Ingår i: SILICON PHOTONICS AND PHOTONIC INTEGRATED CIRCUITS II. - : SPIE. - 9780819481924 ; , s. Q-1-Q-9
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- There is an intense interest on integration of III-V materials on silicon and silicon-on-insulator for realisation of optical interconnects, optical networking, imaging and disposable photonics for medical applications. Advances in photonic materials, structures and technologies are the main ingredients of this pursuit. We investigate nano epitaxial lateral overgrowth (NELOG) of InP material from the nano openings on a seed layer on the silicon wafer, by hydride vapour phase epitaxy (HVPE). The grown layers were analysed by cathodoluminescence (CL) in situ a scanning electron microscope, time-resolved photoluminescence (TR-PL), and atomic force microscope (AFM). The quality of the layers depends on the growth parameters such as the V/III ratio, growth temperature, and layer thickness. CL measurements reveal that the dislocation density can be as low as 2 - 3.10(7) cm(-2) for a layer thickness of similar to 6 mu m. For comparison, the seed layer had a dislocation density of similar to 1.10(9) cm(-2). Since the dislocation density estimated on theoretical grounds from TRPL measurements is of the same order of magnitude both for NELOG InP on Si and on InP substrate, the dislocation generation appears to be process related or coalescence related. Pertinent issues for improving the quality of the grown InP on silicon are avoiding damage in the openings due to plasma etching, pattern design to facilitate coalescence with minimum defects and choice of mask material compatible with InP to reduce thermal mismatch.
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| 7. |
- Junesand, Carl, 1981-, et al.
(författare)
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Optimisation of seed and mask surfaces in epitaxial lateral overgrowth of indium phosphide on silicon for silicon photonics
- 2011
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Ingår i: Conference Proceedings. - : VDE VERLAG GMBH. - 9783800733569 - 9781457717536 ; , s. 1-4
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Konferensbidrag (refereegranskat)abstract
- The effect of chemical mechanical polishing (CMP) on epitaxial lateral overgrowth (ELOG) of InP is investigated. To this end, silicon wafers with a seed layer of InP has been treated in two ways; by depositing SiO2 mask and polishing it prior to performing ELOG, and by growing additional InP directly on the InP/Si wafer and then polishing the InP layer prior to depositing and patterning SiO2 followed by subsequent ELOG. For InP seed, a two step process with Chemlox™ slurry and sodium hypochlorite mixed with citric acid-based slurry has been used whereas for SiO2 surface polishing, only one slurry was employed. Analysis of the ELOG layers has been carried out with atomic force microscope (AFM) and panchromatic cathodoluminescence (PC-CL) in-situ a scanning electron microscope (SEM). The results show that polishing the InP/Si layer has not only a beneficial effect on surface morphology of the ELOG layer but also on reduction of its defect density as a consequence of improved conditions for near-ideal coalescence.
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| 8. |
- Junesand, Carl, et al.
(författare)
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Study of planar defect filtering in InP grown on Si by epitaxial lateral overgrowth
- 2013
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Ingår i: Optical Materials Express. - : Optical Society of America. - 2159-3930 .- 2159-3930. ; 3:11, s. 1960-1973
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Tidskriftsartikel (refereegranskat)abstract
- InP thin films have been grown on InP/Si substrate by epitaxial lateral overgrowth (ELOG). The nature, origin and filtering of extended defects in ELOG layers grown from single and double openings in SiO2 mask have been investigated. Whereas ELOG layers grown from double openings occasionally exhibit threading dislocations (TDs) at certain points of coalescence, TDs are completely absent in ELOG from single openings. Furthermore, stacking faults (SFs) observed in ELOG layers grown from both opening types originate not from coalescence, but possibly from formation during early stages of ELOG or simply propagate from the seed layer through the mask openings. A model describing their propagation is devised and applied to the existent conditions, showing that SFs can effectively be filtered under certain conditions. ELOG layers grown from identical patterns on InP substrate contained no defects, indicating that the defect-forming mechanism is in any case not inherent to ELOG itself.
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| 9. |
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| 10. |
- Kataria, Himanshu, et al.
(författare)
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Carrier-transport, optical and structural properties of large area ELOG InP on Si using conventional optical lithography
- 2013
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Ingår i: 2013 International Conference on Indium Phosphide and Related Materials (IPRM). - : IEEE conference proceedings. - 9781467361309 - 9781467361316 ; , s. 6562592-
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Konferensbidrag (refereegranskat)abstract
- We present the carrier-transport, optical and structural properties of InP deposited on Si by Epitaxial Lateral Overgrowth (ELOG) in a Low Pressure-Hydride Vapor phase epitaxy (LP-HVPE). Hall measurements, micro photoluminescence (μ-PL) and X-ray diffraction (XRD) were used to study the above-mentioned respective properties at room temperature. It is the first time that electrical properties of ELOG InP on Si are studied by Hall measurements. Prior to ELOG, etching of patterned silicon dioxide (SiO2) mask leading to a high aspect ratio, i. e. mask thickness to opening width >2 was optimized to eliminate defect propagation even above the opening. Dense high aspect ratio structures were fabricated in SiO2 to obtain ELOG InP on Si, coalesced over large area, making it feasible to perform Hall measurements. We examine this method and study Hall mobility, strain and optical quality of large area ELOG InP on Si.
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