Browsing by Author "Chu, J. T."

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Abnormal PL spectrum in InGaN MQW surface emitting cavity
(2008-01-01)
Chu, J. T.
;
Cheng, Y. -J.
;
Kuo, H. C.
;
Lu, T. C.
;
Wang, S. C.
We report the observation of an abnormal photoluminescent (PL) spectrum from a HeCd laser pumped InGaN multiple quantum well (MQW) vertical cavity. The device is fabricated using standard MOCVD deposition on a (0001)-oriented sapphire substrate. The layer structures are: 10nm nucleation layer, a 4um bulk GaN layer, InGaN MQWs, and a final 200nm GaN cap layer. The InGaN MQWs consist of 10 pairs of 5 nm GaN barrier and 3 run In0.1Ga0.9N well. The peak emission of the as-grown MQWs sample was similar to 420nm. A dielectric distributed Bragg reflectors (DBR) were then coated on the top layer, followed by a laser lift off from sapphire substrate, and subsequently another DBR coated on the bulk GaN bottom surface. The cavity has a quality factor of similar to 520 from 400-490nm. The device was pumped by a focused CW HeCd laser from the bulk GaN side. When the laser is focused onto the InGaN MQWs, a photoluminescent spectrum centered at the designed MOW wavelength was observed as expected. However, when the focused position was moved toward the bulk GaN region, an additional abnormal PL peak around 460nm was observed. This is far outside the designed MQW wavelength.
Abnormal PL spectrum in InGaN MQW surface emitting cavity - art. no. 69080L
(2008)
Chu, J. T.
;
Cheng, Y. -J.
;
Kuo, H. C.
;
Lu, T. C.
;
Wang, S. C.
We report the observation of an abnormal photoluminescent (PL) spectrum from a HeCd laser pumped InGaN multiple quantum well (MQW) vertical cavity. The device is fabricated using standard MOCVD deposition on a (0001)-oriented sapphire substrate. The layer structures are: 10nm nucleation layer, a 4um bulk GaN layer, InGaN MQWs, and a final 200nm GaN cap layer. The InGaN MQWs consist of 10 pairs of 5 nm GaN barrier and 3 run In0.1Ga0.9N well. The peak emission of the as-grown MQWs sample was similar to 420nm. A dielectric distributed Bragg reflectors (DBR) were then coated on the top layer, followed by a laser lift off from sapphire substrate, and subsequently another DBR coated on the bulk GaN bottom surface. The cavity has a quality factor of similar to 520 from 400-490nm. The device was pumped by a focused CW HeCd laser from the bulk GaN side. When the laser is focused onto the InGaN MQWs, a photoluminescent spectrum centered at the designed MOW wavelength was observed as expected. However, when the focused position was moved toward the bulk GaN region, an additional abnormal PL peak around 460nm was observed. This is far outside the designed MQW wavelength.
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.
;
Ou-Yang, M. C.
;
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.
;
Lai, C. F.
;
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.
Improvement of InGaN/GaN light emitting diode performance with a nano-roughened p-GaN surface by excimer laser-irradiation
(2006-10-10)
Huang, Hung-Wen
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Kao, C. C.
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Chu, J. T.
;
Liang, W. D.
;
Kuo, H. C.
In this paper, we reported the InGaN/GaN light emitting diode (LED) with a nano-roughened top p-GaN surface which caused by KrF excimer laser-irradiation. Comparing with the conventional LED, the brightness of InGaN/GaN light emitting diode (LED) was raised by a factor of 1.25 at 20 mA after KrF excimer laser-irradiation (250 mJ cm(-2) at 248 nm for 25 ns). Meanwhile, the operation voltage of InGaN/GaN LED was reduced from 3.55 to 3.3 V at 20 mA with 29% reduction in the series resistance. The causes for the brightness increase can be attributed to laser-irradiation induced nano-roughening of p-GaN surface. The reduction in the series resistance can be attributed to the increased contact area of nano-roughened surface and higher hole concentration after laser-irradiation. (c) 2005 Published by Elsevier B.V.
Light-output enhancement of nano-roughened GaN laser lift-off light-emitting diodes formed by ICP dry etching
(2007-05-01)
Kao, Chih-Chiang
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Kuo, H. C.
;
Yeh, K. F.
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Chu, J. T.
;
Peng, W. L.
In this paper, we report the fabrication and characteristics of nano-roughened GaN laser lift-off (LLO) light-emitting diodes (LEDs) with different scale surface roughness. The surface roughness of devices was controlled by inductively coupled plasma reactive inn etching. Using this fabrication method to form nanoscaled roughness, the electrical property was almost not degraded. Furthermore, the light-output power and wall-plug efficiency of LLO LED could be both significantly enhanced about two times using this simple method.