Browsing by Author "Wang, Te-Chung"

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Characteristics of a-Plane Green Light-Emitting Diode Grown on r-Plane Sapphire
(2009-08-15)
Ling, Shih-Chun
;
Wang, Te-Chung
;
Chen, Jun-Rong
;
Liu, Po-Chun
;
Ko, Tsung-Shine
In this work, we have successfully grown a-plane green light-emitting diodes (LEDs) on r-plane sapphire and investigated the device characteristics of a-plane green LEDs. The apparent emission polarization anisotropy was observed and the polarization degree was as high as 67.4%. In addition, the electroluminescence (EL) spectra first revealed a wavelength blue-shift with increasing drive current to 20 mA, which could be attributed to the band-filling effect, and then the EL peak become constant. The current-voltage curve showed the forward voltage of a-plane LED grown on r-plane sapphire substrate was 3.43 V and the differential series resistance was measured to be about 24 Omega as 20-mA injected current. Furthermore, the output power was 240 mu W at 100-mA drive current.
Characteristics of ultraviolet nonpolar InGaN/GaN light-emitting diodes using trench epitaxial lateral overgrowth technology
(2007)
Ling, Shih-Chun
;
Wang, Te-Chung
;
Ko, Tsung-Shine
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
Ultraviolet nonpolar InGaN/GaN light-emitting diodes were grown on trench epitaxial lateral overgrowth (TELOG) a-plane GaN template by metalorganic chemical vapor deposition. Electroluminescence measurements revealed main peak at 373 nm when injection current was 40 mA. Furthermore, cathodeluminescence observed the low-defect density wings emitted 373 run peak and the TELOG coalescence areas emitted 443 nm due to different incorporation of indium, Meanwhile, polarization measurement shown a degree of ultraviolet peak is 28.7%.
Characteristics of ultraviolet nonpolar InGaN/GaN light-emitting diodes using trench epitaxial lateral overgrowth technology
(2008-04-01)
Ling, Shih-Chun
;
Wang, Te-Chung
;
Ko, Tsung-Shine
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
Ultraviolet nonpolar InGaN/GaN light-emitting diodes grown on trench epitaxial lateral overgrowth (TELOG) a-plane GaN template by metalorganic chemical vapor deposition were fabricated. Two emission peaks at 373 and 443 nm are observed from each fabricated device. The double emission peaks feature is identified by cathodoluminescence images, which show that the ultraviolet peak is emitted from the low-defect density wings on the TELOG and the blue peak is emitted from the TELOG-coalesced seed areas due to different incorporation of indium. The L-I-V diagram revealed that there are leakage current pathways due to the many threading dislocations in seed regions, and that the output power reached 0.2 mW at 140 mA. Two electroluminescence (EL) peaks are observed simultaneously when the driving current is below 50 mA. However, the EL peak at 373 nm dominates when current is above 50 mA. In addition, the degree of polarization of the ultraviolet peak was measured and found to be 28.7%. (C) 2008 Elsevier B.V. All rights reserved.
Experimental and theoretical analysis on ultraviolet 370 nm AlGaInN light-emitting diodes
(2006-05-01)
Chang, Yi-An
;
Yen, Sheng-Horng
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Wang, Te-Chung
;
Kuo, Hao-Chung
;
Kuo, Yen-Kuang
An ultraviolet (UV) AlGaInN light-emitting diode (LED) with 370 nm emission is demonstrated. At room temperature (RT) UV power of 0.8 mW at 20 mA with 3.6 V operation voltage is achieved. It provides 4 mW output when driven at 125 mA under continuous-wave (CW) operation. Qualitative optimization of the Al composition in the AlGaN electron-block layer and the quaternary AlGaInN quantum well (QW) number of the UV LED is also investigated in this study. The numerical results fit with the experimentally demonstrated output performance of our AlGaInN UV LED. We find that the UV AlGaInN LED can provide better output characteristics when the Al composition in the AlGaN electron-block layer is in the range 19-21 % and the AlGaInN QW number is in the range 5-7 by reducing the electron leakage current.
Internal quantum efficiency behavior of a-plane and c-plane InGaN/GaN multiple quantum well with different indium compositions
(2008)
Wang, Te-Chung
;
Ko, Tsung-Shine
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
;
Gao, Run-Ci
We had investigated the potential of non-polar a-plane InGaN/GaN multiple quantum well (MQW) for high indium content blue/green emission. By comparisons of a-plane and c-plane MQW with different indium, compositions, we concluded that without piezoelectric field, high indium. content non-polar a-plane InGaN/GaN MQW is suitable for green light emitting diode (LED). Furthermore, similar to c-plane GaN InGaN/GaN MQW, the localized state might enhance the performance of a-plane MQW while the indium composition about 24% although the threading dislocation density (TDD) is quite high. On the other hand, the indium phase separation might also occur on a-plane InGaN/GaN MQW while the indium. composition about 30% so that the photoluminescence intensity of the sample 810 degrees C low down and spectrum bandwidth broaden.
Lasing characteristics of a GaN photonic crystal nanocavity light source
(2007-07-23)
Lai, Chun-Feng
;
Yu, Peichen
;
Wang, Te-Chung
;
Kuo, Hao-Chung
;
Lu, Tien-Chang
Lasing characteristics from photonic crystal defects fabricated on bulk GaN are investigated. The device demonstrates multimode lasing with linewidths as narrow as 2-3 angstrom, and an enhanced spontaneous emission factor beta similar to 0.045. The emission spectra indicate that the laser emission is initiated horizontally in the defect nanocavity and then coupled to the vertical radiation, possibly via photonic crystal Bloch modes or by scattering.
Material and optical properties of trenched epitaxial lateral overgrowth of a-plane GaN
(2007)
Wang, Te-Chung
;
Lu, Tien-Chang
;
Ko, Tsung-Shine
;
Kuo, Hao-Chung
;
Chen, Hou-Guang
The crystal quality of a-plane GaN film was successfully improved by using trenched epitaxial lateral overgrowth (TELOG) of a-plane GaN. Not only the threading dislocation density but also the difference of anisotropic in-plane strain between orthogonal crystal axes can be mitigated by using TELOG. The low threading dislocation density investigated by transmission electron microscopy was estimated to be 3 x 10(7) cm(-2) on the N-face GaN wing. According the results of mu-PL and CL, the threading dislocations are the strongly non-radiative center in a-plane GaN film. Finally, we concluded that a narrower stripped GaN seeds and deeper stripped trenches etched into the surface of sapphire could derive a better quality a-plane GaN film.
Performance Enhancement of a-Plane Light-Emitting Diodes Using InGaN/GaN Superlattices
(2009-04-01)
Ling, Shih-Chun
;
Wang, Te-Chung
;
Chen, Jun-Rong
;
Liu, Po-Chun
;
Ko, Tsung-Shine
We have fabricated a-plane light-emitting diodes (LEDs) with inserted InGaN/GaN superlattices. The structural characteristics and device performance of a-plane light-emitting diodes with/without superlattices were also identified. Transmission electron microscope (TEM) images revealed that the threading dislocation (TD) density for the sample using superlattices was reduced from 3 x 10(10) cm(-2) down to similar to 9 x 10(9) cm(-2). The electroluminescence (EL) intensity of the sample with InGaN/GaN superlattices was enhanced by a factor of 3.42 times to that of the conventional sample without InGaN/GaN superlattices. Furthermore, we observed that the polarization degree of a-plane LEDs with superlattices (56.3%) was much higher than that without superlattices (27.4%). A series of experiments demonstrated that the feasibility of using InGaN/GaN superlattices for the TD reduction and the improvement of luminescence performance in a-plane III-nitride devices. (C) 2009 The Japan Society of Applied Physics
Trenched epitaxial lateral overgrowth of fast coalesced a-plane GaN with low dislocation density
(2006-12-18)
Wang, Te-Chung
;
Lu, Tien-Chang
;
Ko, Tsung-Shine
;
Kuo, Hao-Chung
;
Yu, Min
The crystal quality of a-plane GaN films was improved by using epitaxial lateral overgrowth on trenched a-plane GaN buffer layers. Not only the threading dislocation density but also the difference of anisotropic in-plane strain between orthogonal crystal axes can be mitigated by using trenched epitaxial lateral overgrowth (TELOG). The low threading dislocation density investigated by the cross-sectional transmission electron microscopy was estimated to be 3x10(7) cm(-2) on the N-face GaN wing. On the other hand, the Ga-face GaN wing with a faster lateral overgrowth rate could be influenced by the thin GaN layer grown on the bottom of the trenches, resulting in higher dislocation density generated. As a result, the authors concluded that a narrower stripped GaN seeds and deeper stripped trenches etched into the surface of sapphire could derive a better quality a-plane GaN film. Finally, they demonstrated the fast coalescence process of TELOG GaN films below 10 mu m thick. (c) 2006 American Institute of Physics.
Ultraviolet Lasing Characteristics of a GaN Photonic Crystal Defect Emitter
(2007)
Lai, Chun-Feng
;
Yu, Peichen
;
Wang, Te-Chung
;
Kuo, Hao-Chung
;
Lu, Tien-Chang
The fabricated GaN photonic crystal defect emitter demonstrated multimode lasing with a low optical pumping threshold of pulse engergy similar to 0.15 mu J. The device exhibited high spectral purity and enhanced spontaneous emission factor, beta similar to 0.045. (C) 2006 Optical Society of America