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24 results on '"Choi, R. J."'

3. High-density plasma-induced etch damage of InGaN/GaN multiple quantum well light-emitting diodes.

Author

Hahn, Y. B., Choi, R. J., Hong, J. H., Park, H. J., Choi, C. S., and Lee, H. J.

Subjects
*LIGHT emitting diodes, *QUANTUM wells, *INDIUM compounds, *GALLIUM nitride
Abstract

Plasma-induced damage of InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) has been studied in terms of forward turn-on and reverse breakdown voltages, together with etch rate and surface morphology. The physical degradation of sidewall along with rough surface morphology of n-GaN caused by increased ion scattering induced the deterioration of the forward and reverse voltages. The forward turn-on voltage was relatively independent of the pressure up to 20 mTorr. The reverse breakdown voltage showed the worst degradation at 75% Cl[sub 2] mainly because of a sidewall contamination. It was found that the turn-on voltage is sensitive to the surface roughness of the etched n-GaN and the breakdown voltage is strongly affected by the sidewall contamination. Annealing under nitrogen after the mesa etching improved the electrical properties of the InGaN/GaN MQW LEDs. [ABSTRACT FROM AUTHOR]

Published
2002
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4. Two different behavior patterns of photoluminescence depending on Mg doping rate in p-type GaN epilayers.

Author

Jeong, S. M., Shim, H. W., Yoon, H. S., Cheong, M. G., Choi, R. J., Suh, E.-K., and Lee, H. J.

Subjects
GALLIUM nitride, CHEMICAL vapor deposition, CHEMICAL structure
Abstract

Mg-doped p-type GaN epilayers grown by metalorganic chemical vapor deposition exhibit two different types of photoluminescence (PL) characteristics depending on Mg doping rate; the existence of critical Mg concentration is found where both electrical and optical characteristics show an abrupt change in their behavior. In samples with relatively low Mg concentration, a band edge emission, a peak associated with shallow donor-acceptor pair recombination, and a 2.8 eV blue band emission appear in the PL spectrum. Intensities of all three PL peaks decrease with increasing annealing temperature; the blue band quenches most rapidly. In contrast, in samples grown with high ratio of Mg/Ga flow rate, only a strong blue emission band is observed and the intensity of the blue band increases with the annealing temperature suggesting a different origin from the blue band of lightly doped samples. From the annealing temperature dependence of the blue band intensity, we speculate that the emission mechanism of the blue band in relatively lightly Mg-doped GaN epilayers involves Mg-related deep level complexes such as substitutional/interstitial Mg-related complexes. On the other hand, a model involving a formation of pyramidal defects and the presence of Mg-rich inclusions which modifies the dominant optical transition can be a possible explanation for the origin of the blue band in heavily doped ones. [ABSTRACT FROM AUTHOR]

Published
2002
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5. Effects of growth interruption on the optical and the structural properties of InGaN/GaN quantum wells grown by metalorganic chemical vapor deposition.

Author

Cheong, M. G., Yoon, H. S., Choi, R. J., Kim, C. S., Yu, S. W., Hong, C.-H., Suh, E.-K., and Lee, H. J.

Subjects
QUANTUM wells, MICROSCOPY, OPTICAL properties
Abstract

Effects of growth interruption on the optical and the structural properties of InGaN/GaN quantum wells were investigated by using photoluminescence, transmission electron microscopy, optical microscopy, and high resolution x-ray diffraction. The In[sub x]Ga[sub 1-x]N/GaN (x>0.2) quantum wells used in this study were grown on c-plane sapphire by using metalorganic chemical vapor deposition. The interruption was carried out by closing the group-III metalorganic sources before and after the growths of the InGaN quantum well layers. The transmission electron microscopy images show that with increasing interruption time, the quantum-dot-like regions and well thickness decreased due to indium reevaporation or the thermal etching effect. As a result the photoluminescence peak position was blueshifted and the intensity was reduced. Temperature- and excitation-power-dependent photoluminescence spectra support the results of transmission electron microscopy measurements. The sizes and the number of V defects did not differ with the interruption time. The interruption time is not directly related to the formation of defects. The V defect originates at threading dislocations and inversion domain boundaries due to higher misfit strain. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2001
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6. PDE-4 Inhibition Rescues Aberrant Synaptic Plasticity in Drosophila and Mouse Models of Fragile X Syndrome

Author

Choi, C. H., primary, Schoenfeld, B. P., additional, Weisz, E. D., additional, Bell, A. J., additional, Chambers, D. B., additional, Hinchey, J., additional, Choi, R. J., additional, Hinchey, P., additional, Kollaros, M., additional, Gertner, M. J., additional, Ferrick, N. J., additional, Terlizzi, A. M., additional, Yohn, N., additional, Koenigsberg, E., additional, Liebelt, D. A., additional, Zukin, R. S., additional, Woo, N. H., additional, Tranfaglia, M. R., additional, Louneva, N., additional, Arnold, S. E., additional, Siegel, S. J., additional, Bolduc, F. V., additional, McDonald, T. V., additional, Jongens, T. A., additional, and McBride, S. M. J., additional

Published
2015
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8. Pharmacological and Genetic Reversal of Age-Dependent Cognitive Deficits Attributable to Decreased presenilin Function

Author

McBride, S. M. J., primary, Choi, C. H., additional, Schoenfeld, B. P., additional, Bell, A. J., additional, Liebelt, D. A., additional, Ferreiro, D., additional, Choi, R. J., additional, Hinchey, P., additional, Kollaros, M., additional, Terlizzi, A. M., additional, Ferrick, N. J., additional, Koenigsberg, E., additional, Rudominer, R. L., additional, Sumida, A., additional, Chiorean, S., additional, Siwicki, K. K., additional, Nguyen, H. T., additional, Fortini, M. E., additional, McDonald, T. V., additional, and Jongens, T. A., additional

Published
2010
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