Browsing by Author "Ling, Shih-Chun"

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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.
Characterization of a-plane green light-emitting diodes using nanorod lateral overgrowth
(2010)
Ling, Shih-Chun
;
Chang, Shih-Pang
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
;
Wang, Shing-Chung
We have demonstrated nanorod lateral overgrowth to reduce dislocation density in a-plane GaN. Subsequently, we grow green a-plane light-emitting diodes using nanorod lateral overgrowth. Output power of 0.5 mW was measured at 20 mA. (C)2010 Optical Society of America
Crystal quality improvement of a-plane GaN using epitaxial lateral overgrowth on nanorods
(2010-04-01)
Ling, Shih-Chun
;
Chao, Chu-Li
;
Chen, Jun-Rong
;
Liu, Po-Chun
;
Ko, Tsung-Shine
The crystal quality of a-plane GaN films was improved by using epitaxial lateral overgrowth on nanorod GaN template. The scanning electron microscope images showed the fully coalesced regrowth process completed within only 2 mu m thickness. The a-plane GaN films grown on nano-rod template showed superior surface quality and less surface pits. The on-axis and off-axis FWHMs of X-ray rocking curves decreased with the increase in the etching depth of the nano-rod template. TEM analysis revealed that the dislocation density was reduced to around 1.2 x 10(9) cm(-2) by the nano-rod epitaxial lateral overgrowth. In addition, the photoluminescence intensity of the a-plane GaN was enhanced significantly. These results demonstrated the opportunity of achieving a-plane GaN films with high crystal quality via nano-rod epitaxial lateral overgrowth. (C) 2009 Elsevier B.V. All rights reserved.
Dislocation reduction in GaN grown on stripe patterned r-plane sapphire substrates
(2007-07-09)
Chen, Hou-Guang
;
Ko, Tsung-Shine
;
Ling, Shih-Chun
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
Extended defect reduction in GaN can be achieved via direct growth on stripe patterned (1(-)1 02) r-plane sapphire substrates by metal organic chemical vapor deposition. The striped mesa is along [11 (-)2 0] with two etched sides in {0001} and {1 (-)1 01} faces. GaN grown on both etched facets in epitaxy exhibit different crystallographic relationships with sapphire substrate which are (1 (-)1 02)(sapphire)parallel to(11 (-)2 0)(GaN) and [11 (-)2 0](sapphire)parallel to[ (-)1 100](GaN), and (0001)(sapphire)parallel to(0001)(GaN) and [11 (-)2 0](sapphire)parallel to[ (-)1 100](GaN), respectively. The dislocation densities can be significantly reduced through epitaxial growth on the inclined lateral faces of mesas. Dislocation density in the order of similar to 10(7) cm(-2) can be achieved in the tilted GaN. (C) 2007 American Institute of Physics.
Growth of semi-polar GaN-based light-emitting diodes grown on an patterned Si substrate
(2011)
Chiu, Ching-Hsueh
;
Lin, Da-Wei
;
Li, Zhen-Yu
;
Ling, Shih-Chun
;
Kuo, Hao-Chung
We present a study of semi-polar (1 (1) over bar 01) InGaN-based light emitting diodes (LEDs) grown on patterned (001) Si substrates by atmospheric-pressure metal organic chemical vapor deposition. A transmission electron microscopy image of the semi-polar template shows that the threading dislocation density was decreased significantly. From electroluminescence measurement, semi-polar LEDs exhibit little blue-shift and low efficiency droop at a high injection current because the reduction of the polarization field not only made the band diagram smoother but also restricted electron overflow to the p-GaN layer as shown in simulations. These results indicate that semi-polar InGaN-based LEDs can possess a high radiative recombination rate and low efficiency droop at a high injection current.
High-reflectivity ultraviolet AlN/AlGaN distributed Bragg reflectors grown by metalorganic chemical vapor deposition
(2008-11-15)
Chen, Jun-Rong
;
Ling, Shih-Chun
;
Hung, Chin-Tsang
;
Ko, Tsung-Shine
;
Lu, Tien-Chang
High-reflectivity ultraviolet distributed Bragg reflectors (DBRs), based on AlN/AlGaN quarter-wave layers, have been designed and grown on 2 in (0001) sapphire substrates by metalorganic chemical vapor deposition. The growth of 20-pair AlN/Al(0.23)Ga(0.77)N DBR shows no observable cracks in the structure and achieves peak reflectivity of 90% at 367 nm together with a stop-band width of 24 nm. Furthermore, the growth of 34-pair AlN/Al(0.23)Ga(0.77)N DBR shows partial cracks from optical microscopy images. According to the room-temperature photoluminescence measurement, the ennission spectrum of 34-pair AlN/Al(0.23)Ga(0.77)N DBR is broader than that of 20-pair AlN/Al(0.23)Ga(0.77)N DBR, which Could be due to strain inhomogeneity generated by cracks. Despite the crystal quality problem, the peak reflectivity of 34-pair AlN/Al(0.23)Ga(0.77)/N DBR could still achieve 97% at 358 nm and the stop-band width is 16nm. (C) 2008 Elsevier B.V. All rights reserved.
Investigation of Emission Polarization and Strain in InGaN-GaN Multiple Quantum Wells on Nanorod Epitaxially Lateral Overgrowth Templates
(2011-09-15)
Huang, Huei-Min
;
Lu, Tien-Chang
;
Chang, Chiao-Yun
;
Ling, Shih-Chun
;
Chan, Wei-Wen
Non-polar (a-plane) InGaN-GaN multiple quantum wells (MQWs) on the GaN nanorod epitaxially lateral overgrowth templates with different nanorod height have been fabricated. The average in-plane strain in the InGaN MQWs has been determined from 2.73 x 10(-2) to 2.58 x 10(-2) while the nanorod height in templates increases from 0 to 1.7 mu m. The polarization ratio of the emission from InGaN MQWs varies from 85% to 53% along with the increase of the GaN nanorod height. The reduction of polarization ratio has been attributed to the partial strain relaxation within the epitaxial structures as a result of growth on the GaN nanorod templates and the micro-size air-voids observed in the nanorod templates.
Investigation of emission polarization and strain in InGaN/GaN multiple quantum wells on nanorod epitaxially lateral overgrowth templates
(2012)
Huang, Huei-Min
;
Lu, Tien-Chang
;
Chang, Chiao-Yun
;
Lan, Yu-Pin
;
Ling, Shih-Chun
Non-polar (a-plane) InGaN/GaN multiple quantum wells (MQWs) on the GaN nanorod epitaxially lateral overgrowth templates with different nanorod height have been fabricated. The average in-plane strain in the InGaN MQWs has been determined from 2.73x10(-2) to 2.58x10(-2) while the nanorod height in templates increases from 0 to 1.7 mu m. The polarization ratio of the emission from InGaN MQWs varies from 85 % to 53 % along with the increase of the GaN nanorod height. The reduction of polarization ratio has been attributed to the partial strain relaxation within the epitaxial structures as a result of growth on the GaN nanorod templates and the micro-size air-voids observed in the nanorod templates.
Low efficiency droop in blue-green m-plane InGaN/GaN light emitting diodes
(2010-06-07)
Ling, Shih-Chun
;
Lu, Tien-Chang
;
Chang, Shih-Pang
;
Chen, Jun-Rong
;
Kuo, Hao-Chung
We investigated the electroluminescence and relatively external quantum efficiency (EQE) of m-plane InGaN/GaN light emitting diodes (LEDs) emitting at 480 nm to elucidate the droop behaviors in nitride-based LEDs. With increasing the injection current density to 100 A/cm(2), the m-plane LEDs exhibit only 13% efficiency droop, whereas conventional c-plane LEDs suffer from efficiency droop at very low injection current density and the EQE of c-plane LEDs decrease to as little as 50% of its maximum value. Our simulation models show that in m-plane LEDs the absence of polarization fields manifest not only the hole distribution more uniform among the wells but also the reduction in electron overflow out of electron blocking layer. These results suggest that the nonuniform distribution of holes and electron leakage current due to strong polarization fields are responsible for the relatively significant efficiency droop of conventional c-plane LEDs. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3449557]
Nanorod epitaxial lateral overgrowth of a-plane GaN with low dislocation density
(2009-06-22)
Ling, Shih-Chun
;
Chao, Chu-Li
;
Chen, Jun-Rong
;
Liu, Po-Chun
;
Ko, Tsung-Shine
The crystal quality of a-plane GaN films was improved by using epitaxial lateral overgrowth on a nanorod GaN template. The investigation of x-ray diffraction showed that the strain in a-plane GaN grown on r-plane sapphire could be mitigated. The average threading dislocation density estimated by transmission electron microscopy was reduced from 3x10(10) to 3.5x10(8) cm(-2). From the temperature-dependent photoluminescence, the quantum efficiency of the a-plane GaN was enhanced by the nanorod epitaxial lateral overgrowth (NRELOG). These results demonstrated the opportunity of achieving a-plane GaN films with low dislocation density and high crystal quality via NRELOG.
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.
Optical Properties of A-Plane InGaN/GaN Multiple Quantum Wells Grown on Nanorod Lateral Overgrowth Templates
(2011-08-01)
Huang, Huei-Min
;
Ling, Shih-Chun
;
Chan, Wei-Wen
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
A-plane InGaN/GaN multiple-quantum wells (MQWs) were grown on a series of nanorod epitaxial lateral overgrowth (NRELOG) templates with varied nanorod depth. Optical properties of these samples were investigated by excitation power and temperature-dependent photoluminescence (PL). Due to the absence of quantum-confined Stark effect, the negligible PL emission peak shift and nearly identical power index for all samples were observed. In contrast to the as-grown MQWs, the thermal activation energy and internal quantum efficiency of NRELOG MQWs exhibit 1.6-fold and 4-fold increases, respectively, which are attributed to the improvement of crystal quality by NRELOG. Furthermore, the Shockley-Read-Hall nonradiative coefficient, determined from the fits of power-dependent PL quantum efficiency, is also apparently reduced while MQWs are grown on NRELOG GaN template. The results show the feasibility to fabricate high radiative efficiency a-plane devices via NRELOG.
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