Browsing by Author "Hsueh, T. H."

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Extraction Efficiency Enhancement of GaN-Based Light-Emitting Diodes by Microhole Array and Roughened Surface Oxide
(2009-05-01)
Lai, Fang-I.
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Ling, S. C.
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Hsieh, C. E.
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Hsueh, T. H.
;
Kuo, Hao-Chung
The light-output power of GaN-based light-emitting diodes (LEDs) was enhanced by microhole array pattern and roughened GaO(x) film grown on the exposed surface. The GaO(x) film was grown by photoelectrochemical (PEC) oxidation via H(2)O and formed a naturally rough oxide surface and GaO(x)/GaN interface. Compared with that of conventional broad-area LEDs, the output power of the microhole array LED and the surface-oxidized microhole array LED increased by 1.38 and 1.82 times at 20-mA forward current, respectively. The results show that the microhole array pattern with the roughened surface oxide method could significantly enhance light extraction efficiency and be a candidate for manufacturing high-efficient low-cost GaN-based LEDs.
Fabrication and photoluminescence of InGaN-based nanorods fabricated by plasma etching with nanoscale nickel metal islands
(2006-07-01)
Huang, H. W.
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Chu, J. T.
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Hsueh, T. H.
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Ou-Yang, M. C.
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Kuo, H. C.
InGaN-based nanorods with a rod density of similar to 3.0 x 10(10) cm(-2) were fabricated from a light-emitting diode structure by an inductively coupled plasma dry-etching with nanoscale nickel metal islands. The nanoscale nickel metal islands were formed from a Ni film by a rapid thermal annealing at 850 degrees C for 1 min. The influence of thicknesses of Ni metal film on the diameter and density of nanorods was also investigated. Structural and optical properties of the InGaN-based nanorods were studied with field-emission scanning electron microscopy, transmission electron microscopy, and photoluminescence. The diameters and heights of nanorods were estimated to be 60-100 nm and more than 0.28 mu m, respectively. The emission-peak wavelength of nanorods showed a blueshift of 5.1 nm from that of the bulk structure. An enhancement by a factor of five times in photoluminescence intensity of nanorods compared to that of the bulk structure was also observed in this work. The blueshift is attributed to the strain relaxation in the well, quantum-confinement effect, or a combination of the two, which result in the enhancement in emission intensity. (c) 2006 American Vacuum Society.
Fabrication of InGaN/GaN nanorod light-emitting diodes with self-assembled Ni metal islands
(2007-11-07)
Chiu, C. H.
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Lu, T. C.
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Huang, H. W.
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Lai, C. F.
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Kao, C. C.
We report the fabrication of InGaN/GaN nanorod light-emitting diodes (LEDs) using inductively coupled plasma reactive-ion etching (ICP-RIE) and a photo-enhanced chemical (PEC) wet oxidation process via self-assembled Ni nanomasks. An enhancement by a factor of six times in photoluminescence (PL) intensities of nanorods made with the PEC process was achieved in comparison to that of the as-grown structure. The peak wavelength observed from PL measurement showed a blue shift of 3.8 nm for the nanorods made without the PEC oxidation process and 8.6 nm for the nanorods made with the PEC oxidation process from that of the as-grown LED sample. In addition, we have demonstrated electrically pumped nanorod LEDs with the electroluminescence spectrum showing more efficiency and a 10.5 nm blue-shifted peak with respect to the as-grown LED sample.
Optical properties of In0.3Ga0.7N/GaN green emission nanorods fabricated by plasma etching
(2007-08-22)
Chiu, C. H.
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Lo, M. H.
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Lai, C. F.
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Lu, T. C.
;
Huang, H. W.
In this study, we have fabricated In0.3Ga0.7N/GaN green emission nanorods and demonstrated optical enhancement by photoluminescence (PL) measurements. An enhancement factor of 3.5 and an emission peak blue-shift of 6.6 nm were observed at 300 K for the green emission nanorods structure in comparison to the as-grown flat surface structure. The blue-shift phenomenon from the nanorod structure could be caused by a partial reduction of the internal piezoelectric field. However, the similar carrier decay time for the green emission nanorod structure and the as-grown flat surface structure observed in low-temperature time-resolved PL measurements indicates that the dominant optical enhancement mechanism of the green emission nanorod structure could be mainly resulting from the large emission surface areas and the multiple scattering paths between the nanorods.