Browsing by Author "Li, Yuh-Jing"

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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.