Browsing by Author "Chen, Yi-Chen"

Now showing 1 - 6 of 6

Lasing action in gallium nitride photonic quasicrystal nanorod arrays
(2012)
Chang, Shih-Pang
;
Sou, Kuok-Pan
;
Chang, Jet-Rung
;
Cheng, Yuh-Jen
;
Li, Yuh-Jing
We report the observation of lasing action from optically pumped gallium nitride nanorod arrays in a quasicrystal pattern. The nanorods were fabricated from a GaN substrate by nanoimprint patterned etching, followed by epitaxial regrowth to form crystalline facets. The imprint was a 12-fold symmetric quasicrystal pattern. The regrowth grew a multiple quantum well core-shell structure on nanorods. The cathodoluminescent emission of quantum wells red shifts from the bottom to top region of nanorod. Under optical pumping, multiple lasing peaks were observed. The lasing modes formed by 12-fold symmetric photonic quasicrystal nanorod arrays are discussed.
Low efficiency droop of InGaN/GaN blue LEDs with super-lattice active structure
(2012)
Chang, Shih-Pang
;
Sou, Kuok-Pan
;
Chang, Jet-Rung
;
Cheng, Yuh-Jen
;
Li, Yuh-Jing
We report the efficiency droop behaviors of InGaN/GaN blue LEDs with different thickness of GaN quantum barriers (QBs). The droop percentage from efficiency peak to 70 A/cm(2) is only about 10% as reducing the thickness of GaN QBs from 104 angstrom to 33 angstrom. A less carrier localization has been observed from wavelength dependent time resoled photoluminescence measurement as reducing the thickness of GaN QBs. The alleviation of droop percentage may due to more uniform distribution of electron and hole carrier in the active region, which resulted from super-lattice (SL) like active structure. The crystalline quality does not become worse from the results of v-pits density even thickness of GaN QBs is as low as 33 angstrom. The SL like active structure could be a potential structure to alleviate the efficiency droop for the application of solid state general lighting.
Optical properties of (1 (1)over-bar 0 1) semi-polar InGaN/GaN multiple quantum wells grown on patterned silicon substrates
(2011-03-01)
Chiu, Ching-Hsueh
;
Lin, Da-Wei
;
Lin, Chien-Chung
;
Li, Zhen-Yu
;
Chen, Yi-Chen
We present a study of high quality (1 (1) over bar 0 1) GaN films and the InGaN/GaN multiple quantum wells (MQWs) using epitaxial lateral overgrowth (ELO) technique by atmospheric pressure metal organic chemical vapor deposition (MOCVD). The smooth coalescence of the stripes and surface morphology was measured by scanning electron microscope (SEM) and atomic force microscopy (AFM). Due to reduction in internal electric field, semipolar InGaN/GaN MQWs have higher radiative recombination rate from time-resolved photoluminescence (TRPL) measurement. In addition, from degree of polarization (DOP) measurement, we observed higher polarization ratio attributed to the induced anisotropic compressive strain. (C) 2010 Published by Elsevier B.V.
Passivation of yellow luminescence defects in GaN film by annealing and CF(4) plasma treatment
(2011-07-01)
Chen, Hsiang
;
Kao, Chyuan-Haur
;
Chen, Yi-Chen
;
Lo, Hong-Kai
;
Yeh, Yih-Min
In this study, we demonstrated that yellow luminescence (YL) defects can be mitigated with proper annealing or CF(4) plasma treatment. Multiple material analyses, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and surface roughness measurements were performed to investigate improvements in GaN film material properties caused by annealing and CF(4) plasma treatment. Filling vacancies during the annealing process and incorporating fluorine atoms to bond with dangling bonds during the plasma treatment process may lessen YL defects and decrease YL luminescence.
Passivation of yellow luminescence defects in GaN film by annealing and CF4 plasma treatment
(2011-07-01)
Chen, Hsiang
;
Kao, Chyuan-Haur
;
Chen, Yi-Chen
;
Lo, Hong-Kai
;
Yeh, Yih-Min
In this study, we demonstrated that yellow luminescence (YL) defects can be mitigated with proper annealing or CF4 plasma treatment. Multiple material analyses, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and surface roughness measurements were performed to investigate improvements in GaN film material properties caused by annealing and CF4 plasma treatment. Filling vacancies during the annealing process and incorporating fluorine atoms to bond with dangling bonds during the plasma treatment process may lessen YL defects and decrease YL luminescence.
Structure and function of TatD exonuclease in DNA repair
(2014-09-15)
Chen, Yi-Chen
;
Li, Chia-Lung
;
Hsiao, Yu-Yuan
;
Duh, Yulander
;
Yuan, Hanna S.
TatD is an evolutionarily conserved protein with thousands of homologues in all kingdoms of life. It has been suggested that TatD participates in DNA fragmentation during apoptosis in eukaryotic cells. However, the cellular functions and biochemical properties of TatD in bacterial and non-apoptotic eukaryotic cells remain elusive. Here we show that Escherichia coli TatD is a Mg2+-dependent 3\'-5\' exonuclease that prefers to digest single-stranded DNA and RNA. TatD-knockout cells are less resistant to the DNA damaging agent hydrogen peroxide, and TatD can remove damaged deaminated nucleotides from a DNA chain, suggesting that it may play a role in the H2O2-induced DNA repair. The crystal structure of the apo-form TatD and TatD bound to a single-stranded three-nucleotide DNA was determined by X-ray diffraction methods at a resolution of 2.0 and 2.9 angstrom, respectively. TatD has a TIM-barrel fold and the single-stranded DNA is bound at the loop region on the top of the barrel. Mutational studies further identify important conserved metal ion-binding and catalytic residues in the TatD active site for DNA hydrolysis. We thus conclude that TatD is a new class of TIM-barrel 3\'-5\' exonuclease that not only degrades chromosomal DNA during apoptosis but also processes single-stranded DNA during DNA repair.