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275 results on '"Weman, H."'

4. Determination of GaAs zinc blende/wurtzite band offsets utilizing GaAs nanowires with an axial GaAsSb insert.

Author

Ahtapodov, L., Kauko, H., Munshi, A. M., Fimland, B. O., van Helvoort, A. T. J., and Weman, H.

Subjects
GALLIUM arsenide, NANOWIRES, SPHALERITE, GALLIUM antimonide, TRANSMISSION electron microscopy, HIGH temperatures, BAND gaps
Abstract

By applying a correlated micro-photoluminescence spectroscopy and transmission electron microscopy (TEM) approach, we have utilized molecular beam epitaxy grown self-catalysed GaAs nanowires (NWs) with an axial GaAsSb insert to determine the band offsets at the crystal phase heterojunction between zinc blende (ZB) and wurtzite (WZ) GaAs. Two distinct PL emission bands originating from the ZB GaAsSb insert were identified. The lower energy PL emission allowed an independent verification of the maximum Sb molar fraction to be ~30%, in agreement with quantitative high-angle annular dark field scanning TEM performed on the same single NW. The higher energy PL emission revealed a low temperature ZB/WZ band offset of 120 meV at the interface between the two GaAs crystal phases occurring at the upper boundary of the insert. Separate conduction and valence band offsets develop at a higher temperature due to the different temperature dependence of the ZB and WZ GaAs band gaps, but both offset values show a relatively little variation in the range of 10-150 K. [ABSTRACT FROM AUTHOR]

Published
2017
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6. Influence of long-range substrate roughness on disorder in V-groove quantum wire structures

Author

Reichardt, H., Leifer, K., Pelucchi, E., Karlsson, K. F., Weman, H., and Rudra A.

Subjects
Gallium arsenide -- Optical properties, Aluminum compounds -- Optical properties, Atomic force microscopy -- Usage, Cathodoluminescence -- Research, Photoluminescence -- Research, Physics
Abstract

Various experiments, including the atomic force microscopy and cathodoluminescnece measurements are used to analyze the influence of long-range substrate roughness in the photoluminescnece spectra of GaAs/ AlGaAs V-groove quantum wires (QWRs). The results demonstrate the effect of long-range substrate roughness on the QWR features.

Published
2006

8. Measuring linear polarization of photoluminescence excitation using a photoelastic modulation technique

Author

Wassermeier, M., Weman, H., Miller, M.S., Petroff, P.M., and Merz, J.L.

Subjects
Photoluminescence -- Research, Modulation (Electronics) -- Methods, Polarization (Light) -- Research, Physics
Abstract

The photoelastic modulation (PEM) technique employed in the study of linear polarization in the photoluminescence emission (PL) and excitation (PLE) of gallium arsenide/aluminum gallium arsenide quantum wire arrays is described. This modulation technique was incorporated into the set-up of the PL and PLE experiments. A theoretical analysis of polarization modulation via the PEM technique is presented while the experimental configuration is discussed and illustrated. The linear polarization of the PL and PLE, which is a result of the lateral confinement in the samples, is tackled. The sensitivity and flexibility of this PEM method separates it from other PL and PLE techniques.

Published
1992

10. Deep-level transient spectroscopy and photoluminescence studies of electron-irradiated Czochralski silicon.

Author

Awadelkarim, O. O., Weman, H., Svensson, B. G., and Lindström, J. L.

Subjects
*MATERIALS at high temperatures, *SILICON, *DEEP level transient spectroscopy, *PHOTOLUMINESCENCE
Abstract

Presents a study which examined the isothermal annealing of electron-irradiated Czochralski silicon samples using deep-level transient spectroscopy and photoluminescence. Background on Czochralski silicon; Experimental setup; Results and conclusions.

Published
1986
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11. Measuring linear polarization of photoluminescence and photoluminescence excitation using a photoelastic modulation technique.

Author

Wassermeier, M., Weman, H., Miller, M. S., Petroff, P. M., and Merz, J. L.

Subjects
*OPTICAL polarization, *PHOTOLUMINESCENCE, *NANOWIRES
Abstract

Presents a study that investigated the polarization dependencies in the low-temperature photoluminescence and photoluminescence excitation of GaAs/AlGaAs quantum wire arrays. Discussion on the features of polarization modulation using a photoelastic modulator; Experiment conducted; Results.

Published
1992
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12. Reactive-ion- and plasma-etching-induced extended defects in silicon studied with photoluminescence.

Author

Weman, H., Lindström, J. L., Oehrlein, G. S., and Svensson, B. G.

Subjects
*SILICON, *PHOTOLUMINESCENCE, *PLASMA etching
Abstract

Presents a study that investigated the defects introduced by reactive-ion etching and plasma etching using deuterium in boron-doped silicon with the photoluminescence technique. Photoluminescence measurements; Secondary-ion mass spectrometry analysis; Shifts in the energy position of the boron bound exciton due to the dry etching treatments.

Published
1990
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13. Electrical and optical properties of gold-doped n-type silicon.

Author

Weman, H., Henry, A., Begum, T., Monemar, B., Awadelkarim, O. O., and Lindström, J. L.

Subjects
*GOLD, *DIFFUSION, *SILICON
Abstract

Presents a study that utilized different measurement techniques, both electrical and optical, to characterize gold (Au) diffusion in n-type float-zoned silicon (Si). Temperature range by Si was measured; Introduction of Au acceptor state; Effects of Au diffusion on the free-carrier concentration and mobilities.

Published
1989
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14. Optimal Solar Cell Efficiency of Radial p-n Junction GaAs/AlGaAs Core-Shell Nanowire Arrays

Author

Lim, C.G. and Weman, H.

Subjects
NEW MATERIALS AND CONCEPTS FOR SOLAR CELLS AND MODULES, Fundamental Material Studies
Abstract

29th European Photovoltaic Solar Energy Conference and Exhibition; 229-231, The effects of intrinsic light trapping or sunlight concentration in nanowire array solar cells comprising of optimally engineered radial p-n junction GaAs/AlxGa1-xAs core-shell nanowires is maximized for optimal solar cell efficiency by optimizing the pitch length of the nanowire array and angles of incidence of the sun-rays. Results reveal that the unique property of core-shell nanowires in decoupling light absorption and carrier collection, along with the exceptionally low optical reflection and strong light trapping, enable radial p-n junction core-shell nanowire array to achieve solar cell efficiencies as high as more than 35% (i.e., exceeding the Shockley-Queisser limit) when illuminated by the one-sun AM1.5G solar spectrum. Such high solar cell efficiencies are the result of the intrinsic sunlight concentration effect in nanowire array solar cell.

Published
2014
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19. Characterization of ZnO Layers Grown by Pulsed Laser Deposition for Hybrid Inorganic/Organic Solar Cells

Author

Weigand, C., Bergren, M., Valset, K., Carey, D., Fagerberg, R., Ladam, C., Grepstad, J., Weman, H., Furtak, T., and Collins, R.

Subjects
Advanced Photovoltaics, New Types of Cells and Modules
Abstract

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 692-695, ZnO nanostructures for use as inorganic acceptors in hybrid inorganic/organic solar cell devices have been grown on Si(001) and c-plane sapphire by pulsed laser deposition (PLD) with and without a Au catalyst. Samples have been characterized by scanning electron microscopy (SEM) and high-resolution x-ray diffraction (XRD). For Au catalyst growth, pure oxygen ambient gas favored ZnO nanosheet growth and vertical ZnO nanorods with (0001) orientation were grown in oxygen-poor ambient gas at 0.5 mbar and 800°C. Decreasing gas pressure led to the growth of ZnO thin films and decreasing temperature promoted ZnO nanosheet formation and increased growth rates. On samples grown without catalyst, ZnO nanorods formed in (0001) orientation at a substrate temperature of 800°C. With decreasing temperature, ZnO thin film growth and an increased deposition rate was observed. This was attributed to less ZnO re-evaporation from the substrate at lower growth temperatures.

Published
2008
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30. Strongly reduced exciton transfer between parallel quantum wires

Author

Karlsson, K.F., Weman, H., Leifer, Klaus, Rudra, A., Kapon, E., Lyo, S.K., Karlsson, K.F., Weman, H., Leifer, Klaus, Rudra, A., Kapon, E., and Lyo, S.K.

Abstract

Exciton transfer between two parallel GaAs V-groove quantum wires or two planar quantum wells separated by AlGaAs barriers ranging from 5.5 nm to 20 nm thickness is studied by photoluminescence and photoluminescence excitation spectroscopy. It is found that the transfer is strongly reduced between the widely spaced quantum wires as compared with quantum wells. This observation is supported by model calculations, which yield strong dimensionality dependence of the photon-exchange transfer.

Published
2007
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32. Polarization-resolved optical absorption in single V-groove quantum wires

Author

Palmgren, S., Weman, H., Schoenberg, A., Karlsson, K.F., Dupertius, M.-A., Leifer, Klaus, Rudra, A., Kapon, E., Palmgren, S., Weman, H., Schoenberg, A., Karlsson, K.F., Dupertius, M.-A., Leifer, Klaus, Rudra, A., and Kapon, E.

Abstract

Optical transitions associated with all three linear polarization directions were investigated in single GaAs V-groove quantum wires of different wire thicknesses. This was accomplished by combining absorption measurements in V-groove waveguide geometry with surface-excited photoluminescence excitation spectroscopy. The observed transitions were identified with the aid of model calculations. It is shown that excitonic intersubband coupling should be accounted for in order to explain the optical transitions associated with confined light-hole-like states. The results are relevant for the design of efficient quantum wire waveguide modulators and lasers. © 2006 American Institute of Physics.

Published
2006
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38. Photocurrent Spectroscopy of Single Wurtzite GaAs Nanowires

Author

Kim, D. C., primary, Ahtapodov, L., additional, Boe, A. B., additional, Choi, J. W., additional, Ji, H., additional, Kim, G. T., additional, Moses, A. F., additional, Dheeraj, D. L., additional, Fimland, B. O., additional, Weman, H., additional, Ihm, Jisoon, additional, and Cheong, Hyeonsik, additional

Published
2011
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