Browsing by Author "Chiu, Ching-Hua"

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Carrier localization degree of In(0.2)Ga(0.8)N/GaN multiple quantum wells grown on vicinal sapphire substrates
(2009-01-01)
Li, Zhen-Yu
;
Lo, Ming-Hua
;
Chiu, Ching-Hua
;
Lin, Po-Chun
;
Lu, Tien-Chang
In this work, we have grown In(0.2)Ga(0.8)N/GaN multiple quantum well (MQWs) epitaxial structure on vicinal sapphire substrates by low pressure metal-organic chemical vapor deposition and investigated the relationship between carrier localization degree and vicinal angles of sapphire substrates. The optical analysis confirmed that the In(0.2)Ga(0.8)N/GaN MQWs grown on 0.2 degrees-off sapphire substrate exhibited the smallest carrier localization degree and more ordered In(0.2)Ga(0.8)N/GaN MQW structure. In addition, mechanisms for carrier localization in In(0.2)Ga(0.8)N/GaN MQWs grown on vicinal substrate were discussed based on the results obtained from the power and temperature dependent photoluminescence measurements. The Raman spectrum showing the in-plane compressive stress of the GaN epitaxial structures grown on vicinal sapphire substrates revealed the relation between the dislocation density and the carrier localization degree in MQWs. From transmission electron microscopy images, the threading dislocation density (TDD) of In(0.2)Ga(0.8)N/GaN MQWs grown on 0.2 vicinal sapphire substrate at the bottom of n-GaN layer was about 9.4 X 10(8) cm(-2) and reduced to 3.0 X 10(8) cm(-2) at the top of n-GaN layer. We also obtained the TDD of 5.6 X 10(7) cm(-2) in the MQW region and only 1.0 X 10(7) cm(-2) in the p-GaN region. Based on the results mentioned above, 0.2 degrees-off substrate can offer In(0.2)Ga(0.8)N/GaN MQW blue light-emitting diode structures with benefits, such as high crystal quality, low defects, and small carrier localization degree. (C) 2009 American Institute of Physics. (DOI: 10.1063/1.3055264)
Carrier localization degree of In0.2Ga0.8N/GaN multiple quantum wells grown on vicinal sapphire substrates
(2009-01-01)
Li, Zhen-Yu
;
Lo, Ming-Hua
;
Chiu, Ching-Hua
;
Lin, Po-Chun
;
Lu, Tien-Chang
In this work, we have grown In0.2Ga0.8N/GaN multiple quantum well (MQWs) epitaxial structure on vicinal sapphire substrates by low pressure metal-organic chemical vapor deposition and investigated the relationship between carrier localization degree and vicinal angles of sapphire substrates. The optical analysis confirmed that the In0.2Ga0.8N/GaN MQWs grown on 0.2 degrees-off sapphire substrate exhibited the smallest carrier localization degree and more ordered In0.2Ga0.8N/GaN MQW structure. In addition, mechanisms for carrier localization in In0.2Ga0.8N/GaN MQWs grown on vicinal substrate were discussed based on the results obtained from the power and temperature dependent photoluminescence measurements. The Raman spectrum showing the in-plane compressive stress of the GaN epitaxial structures grown on vicinal sapphire substrates revealed the relation between the dislocation density and the carrier localization degree in MQWs. From transmission electron microscopy images, the threading dislocation density (TDD) of In0.2Ga0.8N/GaN MQWs grown on 0.2 vicinal sapphire substrate at the bottom of n-GaN layer was about 9.4 X 10(8) cm(-2) and reduced to 3.0 X 10(8) cm(-2) at the top of n-GaN layer. We also obtained the TDD of 5.6 X 10(7) cm(-2) in the MQW region and only 1.0 X 10(7) cm(-2) in the p-GaN region. Based on the results mentioned above, 0.2 degrees-off substrate can offer In0.2Ga0.8N/GaN MQW blue light-emitting diode structures with benefits, such as high crystal quality, low defects, and small carrier localization degree. (C) 2009 American Institute of Physics. (DOI: 10.1063/1.3055264)
Efficiency Enhancement of GaAs Photovoltaics Employing Antireflective Indium Tin Oxide Nanocolumns
(2009-04-27)
Yu, Peichen
;
Chang, Chia-Hua
;
Chiu, Ching-Hua
;
Yang, Chin-Sheng
;
Yu, Jue-Chin
Highly-oriented indium tin oxide nano-columns are prepared by glancing-angle deposition with nitrogen. The tapered column profiles, which function as a graded-refiractive-index layer, offer superior antireflective characteristics. The nano-structured material serves as the conductive antireflective layer for GaAs solar cells, demonstrating a viable efficiency-boosting strategy for next-generation photovoltaics.
Enhanced Light Extraction in Wafer-Bonded AlGaInP-Based Light-Emitting Diodes via Micro- and Nanoscale Surface Textured
(2009-10-01)
Lee, Yea-Chen
;
Kuo, Hao-Chung
;
Cheng, Bo-Siao
;
Lee, Chia-En
;
Chiu, Ching-Hua
AlGaInP-based metal-bonding light-emitting diodes (LEDs) with micro- and nanoscale textured surface were investigated. The device surface with microbowls and nanorods were formed by a chemical wet-etching and dry-etching technique for enhancing light-extraction purpose. The luminous intensity could be enhanced 65.8% under 20-mA current injection as compared with the plane surface LEDs. The maximum wall-plug efficiency was achieved 14.1% at 7.5-mA operation.
Enhancing the Emission Efficiency of In(0.2)Ga(0.8)N/GaN MQW Blue LED by Using Appropriately Misoriented Sapphire Substrates
(2009-01-01)
Li, Zhen-Yu
;
Uen, Wu-Yih
;
Lo, Ming-Hua
;
Chiu, Ching-Hua
;
Lin, Po-Chun
In this paper, we report the fabrication of an In(0.2)Ga(0.8)N/GaN multiple-quantum-well (MQW) structure on vicinal sapphire substrates with a very small offset angle of 0-1 degrees by low-pressure metallorganic chemical vapor deposition. Our study demonstrates that the quality of the In(0.2)Ga(0.8)N/GaN MQW structure is very sensitive to the offset angle of the vicinal substrate. High-resolution X-ray diffraction analyses demonstrated high-order satellite peaks and clear fringes between them for all MQW structures fabricated, from which the interface roughness (IRN) was estimated. The IRN of the In(0.2)Ga(0.8)N/GaN MQW structure fabricated on 0.2 degrees off sapphire substrate was determined as 1.36% of the quantum well layer period. Besides, reciprocal lattice mapping was employed to examine the strain status of the MQW. The lattice relaxation of the same specimen mentioned above was estimated to be 7.4x10(-5). It is therefore manifested that an In(0.2)Ga(0.8)N/GaN MQW structure with abrupt interfaces and good layer periodicity was grown. From it, a shortest radiative lifetime of 14.2 ns and a lowest fluctuation of 5.6 meV in the emission energy of micro-photoluminescence mapping were achieved. In addition, superior material qualities of the whole film fabricated on 0.2 degrees off substrate were recognized by cross-sectional transmission electron microscopy. Based on the results mentioned above, a high-quality In(0.2)Ga(0.8)N/GaN MQW blue light, emitting diode (LED) has been fabricated on 0.2 degrees off substrate, which demonstrated a strong room-temperature electroluminescence emission at the wavelength of 465 nm and with the full width at half maximum of only 19 nm. The same device also showed an output power of 13.4 mW and an external quantum efficiency of 19.2%. Both these characteristics are improved drastically compared with the devices fabricated on the substrates with other offset angles. Conclusively, the use of an appropriately misoriented sapphire substrate is suggested to be effective for elevating the emission efficiency of In(0.2)Ga(0.8)N/GaN MQW blue LED fabricated thereon.
Enhancing the Emission Efficiency of In0.2Ga0.8N/GaN MQW Blue LED by Using Appropriately Misoriented Sapphire Substrates
(2009-01-01)
Li, Zhen-Yu
;
Uen, Wu-Yih
;
Lo, Ming-Hua
;
Chiu, Ching-Hua
;
Lin, Po-Chun
In this paper, we report the fabrication of an In0.2Ga0.8N/GaN multiple-quantum-well (MQW) structure on vicinal sapphire substrates with a very small offset angle of 0-1 degrees by low-pressure metallorganic chemical vapor deposition. Our study demonstrates that the quality of the In0.2Ga0.8N/GaN MQW structure is very sensitive to the offset angle of the vicinal substrate. High-resolution X-ray diffraction analyses demonstrated high-order satellite peaks and clear fringes between them for all MQW structures fabricated, from which the interface roughness (IRN) was estimated. The IRN of the In0.2Ga0.8N/GaN MQW structure fabricated on 0.2 degrees off sapphire substrate was determined as 1.36% of the quantum well layer period. Besides, reciprocal lattice mapping was employed to examine the strain status of the MQW. The lattice relaxation of the same specimen mentioned above was estimated to be 7.4x10(-5). It is therefore manifested that an In0.2Ga0.8N/GaN MQW structure with abrupt interfaces and good layer periodicity was grown. From it, a shortest radiative lifetime of 14.2 ns and a lowest fluctuation of 5.6 meV in the emission energy of micro-photoluminescence mapping were achieved. In addition, superior material qualities of the whole film fabricated on 0.2 degrees off substrate were recognized by cross-sectional transmission electron microscopy. Based on the results mentioned above, a high-quality In0.2Ga0.8N/GaN MQW blue light, emitting diode (LED) has been fabricated on 0.2 degrees off substrate, which demonstrated a strong room-temperature electroluminescence emission at the wavelength of 465 nm and with the full width at half maximum of only 19 nm. The same device also showed an output power of 13.4 mW and an external quantum efficiency of 19.2%. Both these characteristics are improved drastically compared with the devices fabricated on the substrates with other offset angles. Conclusively, the use of an appropriately misoriented sapphire substrate is suggested to be effective for elevating the emission efficiency of In0.2Ga0.8N/GaN MQW blue LED fabricated thereon.
High output power density from GaN-based two-dimensional nanorod light-emitting diode arrays
(2009-04-06)
Lee, Ya-Ju
;
Lin, Shawn-Yu
;
Chiu, Ching-Hua
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
Here we propose and realize a scheme for making a direct contact to a two-dimensional nanorod light-emitting diode (LED) array using the oblique-angle deposition approach. And, more importantly, we demonstrate highly efficient electrical carrier injection into the nanorods. As a result, we show that at a 20 mA dc current injection, the light output power density of our nanorod LED array is 3700 mW cm(-2). More general, this contact scheme will pave the ways for making direct contacts to other kinds of nanoscale optoelectronic devices.
High output power density from GaN-based two-dimensional nanorod light-emitting diode arrays (vol 94, 141111, 2009)
(2009-05-25)
Lee, Ya-Ju
;
Lin, Shawn-Yu
;
Chiu, Ching-Hua
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
InGaN/GaN MQW Nanorods LED Fabricated by ICP-RIE and PEC Oxidation Processes
(2007-01-01)
Lai, Fang-, I
;
Huang, H. W.
;
Chiu, Ching-Hua
;
Lai, C. F.
;
Lu, T. C.
The InGaN/GaN nanorods LED was successfully fabricated by ICP-RIE and PEC processes. Compared with as-grown sample, the PL and EL peak-wavelengths of the nanorods with PEC show 8.6 and 10.5 nm blue-shift, respectively. (c) 2007 Optical Society of America
Investigation of light absorption properties and acceptance angles of nanopatterned GZO/a-Si/p(+)-Si photodiodes
(2010-05-28)
Chen, Cheng-Pin
;
Lin, Pei-Hsuan
;
Hung, Yen-Jen
;
Hsu, Shao-Shun
;
Chen, Liang-Yi
In this work, n-GZO/a:amorphous-Si(i:intrinsic)/p(+)-Si photodiodes are fabricated. We employed a nanosphere lithographic technique to obtain nanoscale patterns on either the a-Si(i) or p(+)-Si surface. As compared with the planar n-GZO/p(+)-Si diode, the devices with nanopatterned a-Si(i) and nanopatterned p(+)-Si substrates show a 32% and 36.2% enhancement of photoresponsivity. Furthermore, the acceptance angle measurement reveals that the nanostructured photodiodes have larger acceptance angles than the planar structure. It also shows that the device with the nanocone structure has a higher acceptance angle than that with the nanorod structure.
Making a direct electrical contact to InGaN/GaN nanorod LEDs: high output power density
(2009-01-01)
Lee, Ya-Ju
;
Lin, Shawn-Yu
;
Chiu, Ching-Hua
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
We realize a new scheme for making a direct contact to a two-dimensional (2D) nanorod LED array using the oblique-angle deposition. More importantly, we demonstrate highly efficient carrier injection into the nanorods. (C) 2006 Optical Society of America
Metal organic chemical vapor deposition growth of GaN-based light emitting diodes with naturally formed nano pyramids
(2008-04-01)
Chiu, Ching-Hua
;
Lee, Chia-En
;
Lo, Ming-Hua
;
Huang, Hung-Wen
;
Lu, Tien-Chang
GaN-based light-emitting diodes (LEDs) with naturally formed nano pyramids roughened surfaces grown by metal organic chemical vapor deposition (MOCVD) were demonstrated. In this study, Mg-treatment, a growth-.interruption step and a surface treatment using biscyclopentadienyl magnesium (CP(2)Mg), was performed to form the nano pyramids on the surface of a p-type cladding layer, and then a p-type contact layer was grown on the p-type cladding layer, so as to create a p-type contact layer with a rough surface. Assisted by the nano pyramids surface roughening process, the light output power of the LEDs reached 11.3 and 9.7 mW with 10 and 5 min Mg-treatment at a driving current of 20 mA. The light outputs were increased by 48 and 27%, respectively, compared with the results from the LED without Mg-treatment.
Method for promoting light emission efficiency of LED using nanorods structure
(2008-12-11)
Huang, Hung-Wen
;
Lu, Tien-Chang
;
Chiu, Ching-Hua
;
Kuo, Hao-Chung
;
Wang, Shing-Chung
Method for the light emitting diode (LED) having the nanorods-like structure is provided. The LED employs the nanorods are subsequently formed in a longitudinal direction by the etching method and the PEC method. In addition, the plurality of the nanorods is arranged in an array so that provide the LED having much greater brightness and higher light emission efficiency than the conventional LED.
Nano-processing techniques applied in GaN-Based light-emitting devices with self-assembly Ni nano-masks
(2008-05-01)
Chiu, Ching-Hua
;
Lo, Ming-Hua
;
Lu, Tien-Chang
;
Yu, Peichen
;
Huang, H. W.
We have developed a simple method to fabricate nanoscale masks by using self-assembly Ni clusters formed through a rapid thermal annealing (RTA) process. The density and dimensions of the Ni nano-masks could be precisely controlled. The nano-masks were successfully applied to GaN-based light-emitting diodes (LEDs) with nano-roughened surface, GaN nanorods, and GaN-based nanorod LEDs to enhance light output power or change structure properties. The GaN-based LED with nano-roughened surface by Ni nano-masks and excimer laser etching has increased 55% light output at 20 mA when compared to that without the nano-roughened process. The GaN nanorods fabricated by the Ni nano-masks and ICP-RIE dry etching showed 3.5 times over the as-grown sample in photoluminescence (PL) intensity. The GaN-based nanorod LEDs assisted by photo-enhanced chemical (PEC) wet oxidation process were also demonstrated. The electroluminescence (EL) intensity of the GaN-based nanorod LED with PEC was about 1.76 times that of the as-grown LED. The fabrication, structure properties, physical features, and the optical and electrical properties of the fabricated devices will be discussed.
NANOSTRUCTURED THIN-FILM FORMED BY UTILIZING OBLIQUE-ANGLE DEPOSITION AND METHOD OF THE SAME
(2010-10-14)
Chang, Chia-Hua
;
Yang, Chin-Sheng
;
Chiu, Ching-Hua
;
Yu, Pei-Chen
;
Kuo, Hao-Chung
The present invention discloses a transparent conductive nanostructured thin-film by oblique-angle deposition and method of the same. An electron beam system is utilized to evaporate the target source. Evaporation substrate is disposed on a plurality of adjustable sample stage. Multiple gas control valve and heat source is provided to control the gas flow and temperature within the process chamber. An annealing process is performed after the evaporation to improve the thin-film structure and optoelectronic properties.
Nanostructured thin-film formed by utilizing oblique-angle deposition and method of the same
(2010-02-18)
Chang, Chia-Hua
;
Yang, Chin-Sheng
;
Chiu, Ching-Hua
;
Yu, Pei-Chen
;
Kuo, Hao-Chung
The present invention discloses a transparent conductive nanostructured thin-film by oblique-angle deposition and method of the same. An electron beam system is utilized to evaporate the target source. Evaporation substrate is disposed on a plurality of adjustable sample stage. Multiple gas control valve and heat source is provided to control the gas flow and temperature within the process chamber. An annealing process is performed after the evaporation to improve the thin-film structure and optoelectronic properties.
Reduction of Efficiency Droop in InGaN Light-Emitting Diode Grown on Self-Separated Freestanding GaN Substrates
(2011-06-15)
Chao, Chu-Li
;
Xuan, Rong
;
Yen, Hsi-Hsuan
;
Chiu, Ching-Hsueh
;
Fang, Yen-Hsiang
Using a GaN nanorod template in a hydride vapor phase epitaxy (HVPE) system can manufacture a freestanding GaN (FS-GaN) substrate with threading dislocation densities down to similar to 10(7) cm(-2). In this letter, we report InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) grown on this FS-GaN substrate. The defect densities in the homoepitaxially grown LEDs were substantially reduced, leading to improved light emission efficiency. Compared with the LED grown on sapphire, we obtained a lower forward voltage, smaller diode ideality factor, and higher light-output power in the same structure grown on FS-GaN. The external quantum efficiency (EQE) of LEDs grown on FS-GaN were improved especially at high injection current, which brought the efficiency droop phenomenon greatly reduced at high current density.
Study of the Excitation Power Dependent Internal Quantum Efficiency in InGaN/GaN LEDs Grown on Patterned Sapphire Substrate
(2009-07-01)
Lee, Ya-Ju
;
Chiu, Ching-Hua
;
Ke, Chih Chun
;
Lin, Po Chun
;
Lu, Tien-Chang
The mechanisms of the excitation power dependent internal quantum efficiency in InGaN/GaN multiple quantum wells (MQWs) LEDs grown on the planar and the patterned sapphire substrates (PSS) at temperature of 15 and 300 K were investigated. From observation the tendency of emission peak energy and carrier lifetime variation in MQWs with different excitation power for both LED samples, we conclude the internal quantum efficiency would increase as coulomb screening effect dominates at lower carrier injection stage and decrease due to the band-filling effect at higher density stage. At room temperature, the majority of the initial injected carriers would be first consumed by the thermal activated nonradiative centers that hinder the further achievement of high-efficiency LED devices. Experimentally, the internal quantum efficiency of the LED grown on the PSS is similar to 70% and that of the LED grown on the planar sapphire substrate is similar to 62%. For the LED grown on the PSS, the observed higher internal quantum efficiency is due to the larger activation energy Therefore, the reduction of dislocation defects and the prevention of injected carriers escaping from extended states would be a promising prospective for InGaN/GaN MQWs LEDs to achieve high internal quantum efficiency.