Search

Your search keyword '"Tu, L W"' showing total 156 results
Start Over Author "Tu, L W"
156 results on '"Tu, L W"'

1. Characterizations of strain and defect free GaN nanorods on Si(111) substrates

Author

Seo, H. W., Chen, Q. Y., Iliev, M. N., Chu, W. K., Tu, L. W., Hsiao, C. L., and Meen, James K.

Subjects
Condensed Matter - Materials Science
Abstract

GaN-nanorods grown on Si(111) substrates are found strain- and defect-free as characterized by micro Raman spectroscopy, secondary electron (SE) and cathode-luminescence (CL) imaging. The matrix supporting the nanorods bears the brunt of all strains, strain-relaxations, and defect generations, giving the nanorods an ideal environment to grow to perfection. Photo-excitations by the Raman laser source and electron irradiation during CL imaging lead to an increase of non-equilibrium electrons, suggesting an effective approach to photo-emitting or field emitting device applications. The nanorods, largely isolated from but perfectly aligned with the sustaining matrix, are grown in excellent epitaxy with the Si substrates.

Published
2005

2. Epitaxial GaN Nanorods via Catalytic Capillary Condensation

Author

Seo, H. W., Chen, Q. Y., Tu, L. W., Hsiao, C. L., Iliev, M. N., and Chu, W. K.

Subjects
Condensed Matter - Materials Science
Abstract

Intrinsic catalytic process by capillary condensation of Ga-atoms into nanotrenches, formed among impinging islands during the wurzite-GaN thin film deposition, is shown to be an effective path to growing GaN nanorods without metal catalysts. The nano-capillary brings within it a huge imbalance in equilibrium partial pressure of Ga relative to the growth ambient. GaN nanorods thus always grow out of a holding nanotrench and conform to the boundaries of surrounding islands. The nanorods are epitaxially orientated with <0001>GaN // <111>Si and <2110>GaN // <110>Si similar to the matrix. Concaved geometry is essential and is a condition that limits the axial dimension of the nanorods protruding above the base (matrix) material region. Revelation of the growth mechanism in the current context suggests that fabrication of nano quantum structures with controlled patterns is enabling for any attainable dimensions

Published
2005

12. Unintentional incorporation of hydrogen in wurtzite InN with different surface orientations.

Author

Darakchieva, V., Lorenz, K., Xie, M.-Y., Alves, E., Hsiao, C. L., Chen, L. C., Tu, L. W., Schaff, W. J., Yamaguchi, T., and Nanishi, Y.

Subjects
HYDROGEN, WURTZITE, INDIUM compounds, STRUCTURAL analysis (Engineering), SIMULATED annealing
Abstract

We have studied hydrogen impurities and related structural properties in state-of-the-art wurtzite InN films with polar, nonpolar, and semipolar surface orientations. The effects of thermal annealing and chemical treatment on the incorporation and stability of H are also discussed. The near-surface and bulk hydrogen concentrations in the as-grown films increase when changing the surface orientation from (0001) to ([formula]) to ([formula]) and to ([formula]), which may be associated with a decrease in the grain size and change of the growth mode from 2D to 3D. Thermal annealing at 350oC in N2 leads to a reduction of H concentrations and the intrinsic levels of bulk H are found to correlate with the structural quality and defects in the annealed films. [ABSTRACT FROM AUTHOR]

Published
2011
Full Text
View/download PDF

13. Carrier recombination dynamics in Si doped InN thin films.

Author

Mohanta, Antaryami, Jang, D.-J., Lin, G.-T., Lin, Y.-T., and Tu, L. W.

Subjects
SILICON, INDIUM, THIN films, PHOTOLUMINESCENCE, RADIATION
Abstract

Time-integrated and time-resolved photoluminescence (PL) of InN thin films of different background carrier concentrations are investigated. The PL formation mechanism is attributed to the 'free-to-bound' transition by analyzing the time-integrated PL spectra at different pump fluences. The dependence of the PL decay time with emission energy is investigated using a theoretical model which speculates upon the carrier localization in InN thin films. The radiative lifetime, mobility edge, and carrier localization energy are obtained from the dependence of the PL decay time on emission energy and are studied at different background carrier concentrations. The effect of intervalley scattering between the Γ1 and Γ3 valley on the radiative lifetime, mobility edge, and carrier localization energy is discussed. The longer radiative lifetime and smaller values of the mobility edge and localization energy for 3.06 eV excitation are observed than that for the 1.53 eV excitation due to the intervalley scattering process. [ABSTRACT FROM AUTHOR]

Published
2011
Full Text
View/download PDF

14. Effect of temperature and V/III ratio on the initial growth of indium nitride using plasma-assisted metal-organic chemical vapor deposition.

Author

Norman, D. P., Tu, L. W., Chiang, S. Y., Tseng, P. H., Wadekar, P., Hamad, S., and Seo, H. W.

Subjects
*INDIUM, *NITRIDES, *CHEMICAL vapor deposition, *ORGANIC compounds, *PHYSIOLOGICAL effects of temperature
Abstract

The growth of Indium nitride (InN) was studied in the nucleation stage by metal-organic chemical vapor deposition technique using atomic nitrogen from an RF microwave plasma source. Deposition was carried out through a range of substrate temperatures from 375 to 550 °C and at varying V/III ratios from 950 to 3150. We found that the diffusion lifetime of In atoms on the substrate becomes maximized at the growth temperature 475 °C, in which low temperature photoluminescence exhibits the excellent optical properties of the materials with a bandgap of 0.69 eV and a width of 34 meV. In addition, we observed that nitrogen cracking efficiency is significantly improved by using plasma so that high quality InN crystallites were grown with a very low V/III ratio around 950. [ABSTRACT FROM AUTHOR]

Published
2011
Full Text
View/download PDF

15. Integral Invariants of 3-Manifolds (Commentary on [111], [114])

Author

Tu, Loring W, Tu, L W ( Loring W ), Cattaneo, Alberto Sergio; https://orcid.org/0000-0001-5775-758X, Tu, Loring W, Tu, L W ( Loring W ), and Cattaneo, Alberto Sergio; https://orcid.org/0000-0001-5775-758X

Abstract

These papers arose from my collaboration with Raoul during my stay at Harvard. I was there as a postdoc in physics, in the group of Arthur Jaffe. It was the critical time when I had to decide what to do with my life, including whether I should complete my move to mathematics. At the time I was working on perturbative topological field theories and one day, while I was alone in my office, I was visited by a tall guy who said he was interested in what I was doing and wished to start a collaboration to apply my results.

Published
2018

16. In-vacuum cleaving and coating of semiconductor laser facets using thin silicon and a dielectric.

Author

Tu, L. W., Schubert, E. F., Hong, M., and Zydzik, G. J.

Subjects
*SEMICONDUCTORS, *SILICON, *SURFACE coatings, *LASERS, *SURFACE chemistry
Abstract

Proposes an approach to the coating of semiconductor laser facets, using thin silicon (Si) and band gap dielectric layers. Consequences of the formation of electronic states at the semiconductor surface; Description of the layer sequence and band diagram of the gallium arsenide/α-Si/ Al[sub2]O[sub3] coating; Information on several methods of hydrogen passivation.

Published
1996
Full Text
View/download PDF

20. Role of impurities and dislocations for the unintentional n-type conductivity in InN

Author

Darakchieva, V., Barradas, N. P., Xie, M.-Y., Lorenz, K., Alves, E., Schubert, M., Persson, P. O. A., Giuliani, F., Munnik, F., Hsiao, C. L., Tu, L. W., and Schaff, W. J.

Abstract

We present a study on the role of dislocations and impurities for the unintentional n-type conductivity in high-quality InN grown by molecular beam epitaxy. The dislocation densities and H profiles in films with free electron concentrations in the low 1017 cm-3 and mid 1018 cm-3 range are measured, and analyzed in a comparative manner. It is shown that dislocations alone could not account for the free electron behavior in the InN films. On the other hand, large concentrations of H sufficient to explain, but exceeding substantially, the observed free electron densities are found. Furthermore, enhanced concentrations of H are revealed at the film surfaces, resembling the free electron behavior with surface electron accumulation. The low-conductive film was found to contain C and it is suggested that C passivates the H donors or acts as an acceptor, producing compensated material in this case. Therefore, it is concluded that the unintentional impurities play an important role for the unintentional n-type conductivity in InN. We suggest a scenario of H incorporation in InN that may reconcile the previously reported observations for the different role of impurities and dislocations for the unintentional n-type conductivity in InN.

Published
2009

22. Unintentional incorporation of hydrogen in wurtzite InN with different surface orientations

Author

Darakchieva, Vanya, Lorenz, K, Xie, Mengyao, Alves, E, Hsiao, C L, Chen, L C, Tu, L W, Schaff, W J, Yamaguchi, T, Nanishi, Y, Darakchieva, Vanya, Lorenz, K, Xie, Mengyao, Alves, E, Hsiao, C L, Chen, L C, Tu, L W, Schaff, W J, Yamaguchi, T, and Nanishi, Y

Abstract

We have studied hydrogen impurities and related structural properties in state-of-the-art wurtzite InN films with polar, nonpolar, and semipolar surface orientations. The effects of thermal annealing and chemical treatment on the incorporation and stability of H are also discussed. The near-surface and bulk hydrogen concentrations in the as-grown films increase when changing the surface orientation from (0001) to (000 (1) over bar) to (1 (1) over bar 01) and to (11 (2) over bar0), which may be associated with a decrease in the grain size and change of the growth mode from 2D to 3D. Thermal annealing at 350 degrees C in N(2) leads to a reduction of H concentrations and the intrinsic levels of bulk H are found to correlate with the structural quality and defects in the annealed films., Funding Agencies|FCT Portugal|PTDC/FIS/100448/2008|Swedish Research Council (VR)|2010-3848

Published
2011
Full Text
View/download PDF

23. Hydrogen In Group‐III Nitrides: An Ion Beam Analysis Study

Author

Lorenz, L, Miranda, S. M. C., Barradas, N. P., Alves, E, Nanishi, Y, Schaff, W. J., Tu, L. W., Darakchieva, Vanya, Lorenz, L, Miranda, S. M. C., Barradas, N. P., Alves, E, Nanishi, Y, Schaff, W. J., Tu, L. W., and Darakchieva, Vanya

Abstract

The doping mechanisms of InN, a promising material for novel optoelectronic and electronic devices, are still not well understood. Unintentional hydrogen doping is one possibility that could explain the unintentional n‐type conductivity in high‐quality nominally undoped InN films. We measured a series of state‐of‐the‐art InN samples grown by molecular beam epitaxy with 2 MeV 4He‐ERDA and RBS, showing the presence of relatively high amounts of hydrogen not only at the surface, but also in a deeper layer. Strong depletion of hydrogen due to the analysing beam was observed and taken into account in the analysis. Here, we report on the details of the analysis and show how the results correlate with the free‐electron concentrations of the samples.

Published
2011
Full Text
View/download PDF

24. Hydrogen in InN: A ubiquitous phenomenon in molecular beam epitaxy grown material

Author

Darakchieva, Vanya, Lorenz, K, Barradas, N P, Alves, E, Monemar, Bo, Schubert, M, Franco, N, L Hsiao, C, Chen, L C, Schaff, W J, Tu, L W, Yamaguchi, T, Nanishi, Y, Darakchieva, Vanya, Lorenz, K, Barradas, N P, Alves, E, Monemar, Bo, Schubert, M, Franco, N, L Hsiao, C, Chen, L C, Schaff, W J, Tu, L W, Yamaguchi, T, and Nanishi, Y

Abstract

We study the unintentional H impurities in relation to the free electron properties of state-of-the-art InN films grown by molecular beam epitaxy (MBE). Enhanced concentrations of H are revealed in the near surface regions of the films, indicating postgrowth surface contamination by H. The near surface hydrogen could not be removed upon thermal annealing and may have significant implications for the surface and bulk free electron properties of InN. The bulk free electron concentrations were found to scale with the bulk H concentrations while no distinct correlation with dislocation density could be inferred, indicating a major role of hydrogen for the unintentional conductivity in MBE InN., Original Publication: Vanya Darakchieva, K Lorenz, N P Barradas, E Alves, Bo Monemar, M Schubert, N Franco, C L Hsiao, L C Chen, W J Schaff, L W Tu, T Yamaguchi and Y Nanishi, Hydrogen in InN: A ubiquitous phenomenon in molecular beam epitaxy grown material, 2010, APPLIED PHYSICS LETTERS, (96), 8, 081907. http://dx.doi.org/10.1063/1.3327333 Copyright: American Institute of Physics http://www.aip.org

Published
2010
Full Text
View/download PDF

25. Role of impurities and dislocations for the unintentional n-type conductivity in InN

Author

Darakchieva, Vanya, Barradas, N P, Xie, Mengyao, Lorenz, K, Alves, E, Schubert, M, Persson, Per, Giuliani, Finn, Munnik, F, Hsiao, Ching-Lien, Tu, L W, Schaff, W J, Darakchieva, Vanya, Barradas, N P, Xie, Mengyao, Lorenz, K, Alves, E, Schubert, M, Persson, Per, Giuliani, Finn, Munnik, F, Hsiao, Ching-Lien, Tu, L W, and Schaff, W J

Abstract

We present a study on the role of dislocations and impurities for the unintentional n-type conductivity in high-quality InN grown by molecular beam epitaxy. The dislocation densities and H profiles in films with free electron concentrations in the low 10(17) cm(-1) and mid 10(18) cm(-3) range are measured, and analyzed in a comparative manner. It is shown that dislocations alone could not account for the free electron behavior in the InN films. On the other hand, large concentrations of H sufficient to explain, but exceeding substantially, the observed free electron densities are found. Furthermore, enhanced concentrations of H are revealed at the film surfaces, resembling the free electron behavior with surface electron accumulation. The low-conductive film was found to contain C and it is suggested that C passivates the H donors or acts as an acceptor, producing compensated material in this case. Therefore, it is concluded that the unintentional impurities play an important role for the unintentional n-type conductivity in InN. We suggest a scenario of H incorporation in InN that may reconcile the previously reported observations for the different role of impurities and dislocations for the unintentional n-type conductivity in InN.

Published
2009
Full Text
View/download PDF

32. Hydrogen In Group-III Nitrides: An Ion Beam Analysis Study

Author

Lorenz, K., primary, Miranda, S. M. C., additional, Barradas, N. P., additional, Alves, E., additional, Nanishi, Y., additional, Schaff, W. J., additional, Tu, L. W., additional, Darakchieva, V., additional, McDaniel, Floyd D., additional, and Doyle, Barney L., additional

Published
2011
Full Text
View/download PDF

35. GaN/AlN quantum disc single‐nanowire photodetectors

Author

Rigutti, L., primary, Tchernycheva, M., additional, Bugallo, A. De Luna, additional, Jacopin, G., additional, Julien, F. H., additional, Songmuang, R., additional, Monroy, E., additional, Chou, S. T., additional, Lin, Y. T., additional, Tseng, P. H., additional, Tu, L. W., additional, Fortuna, F., additional, Zagonel, L., additional, Kociak, M., additional, and Stephan, O., additional

Published
2010
Full Text
View/download PDF

36. Photogated transistor of III-nitride nanorods

Author

Seo, H. W., primary, Tu, L. W., additional, Chen, Q. Y., additional, Ho, C. Y., additional, Lin, Y. T., additional, Wu, K. L., additional, Jang, D. J., additional, Norman, D. P., additional, and Ho, N. J., additional

Published
2010
Full Text
View/download PDF

40. InN nanotips as excellent field emitters

Author

Wang, K. R., primary, Lin, S. J., additional, Tu, L. W., additional, Chen, M., additional, Chen, Q. Y., additional, Chen, T. H., additional, Chen, M. L., additional, Seo, H. W., additional, Tai, N. H., additional, Chang, S. C., additional, Lo, I., additional, Wang, D. P., additional, and Chu, W. K., additional

Published
2008
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results