Browsing by Author "Ou, Sin-Liang"

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Chemical lift-off process for nitride LEDs from an Eco-GaN template using an AlN/strip-patterned-SiO2 sacrificial layer
(2017-03-01)
Horng, Ray-Hua
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Hsueh, Hsu-Hung
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Ou, Sin-Liang
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Tsai, Chi-Tsung
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Tsai, Tsung-Yen
In this research, a nitride light-emitting diode (LED) fabricated on an electroplated Cu substrate can be removed from a GaN/sapphire (Eco-GaN) template by conducting the chemical lift-off (CLO) process using an AlN/strip-patterned-SiO2 intermediate sacrificial layer. The regrowth GaN epilayer deposited on AlN/patterned SiO2/Eco-GaN can achieve a high crystal quality via the epitaxial lateral overgrowth process. To etch the patterned SiO2 and AlN layers, the HF and 80 degrees C-KOH solutions were used, respectively. Due to the use of low-temperature KOH solution, the GaN epilayer would suffer less damage during the CLO process, improving the reuse feasibility for the Eco-GaN template. Moreover, when the etching treatment was used for the AlN layer, a highly lateral etching rate of 0.5mmh(-1) was achieved. Compared to the conventional LED, the vertical-type LED/Cu substrate had a higher output power of 212mW (at 350mA). Based on our estimation, the output power of LED prepared on Cu substrate had an 86% improvement in comparison to that of conventional LED. Obviously, the good optoelectronic performance of the LED/Cu device can be obtained after performing the CLO process. Furthermore, the separated Eco-GaN template has high potential for reuse applications, indicating that this technique is helpful to the cost-effective LED fabrication.
Effect of Thermal Annealing on a-plane GaN Grown on r-plane Sapphire
(2014)
Ko, Tsung-Shine
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Lu, Tien-Chang
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Chen, Jung-Ron
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Ou, Sin-Liang
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Chang, Chia-Ming
The crystal quality improvement of a-plane GaN grown on r-plane sapphire was demonstrated by applying thermal annealing on as-grown samples in nitrogen ambient. The root mean square roughness of the 1000 degrees C-annealed a-plane GaN was only 0.4 nm measured by atomic force microscopy. Transmission electron microscopy results further indicate threading dislocations were decreased from 5x10(10) cm(-2) to 1.5x10(10) cm(-2) along [0001] GaN and stacking faults were decreased from 8.7x 10(5) cm(-1) to 4.8x 10(5) cm(-1) after the sample was annealed at 1000 degrees C. Room temperature photo luminescence measurements showed band edge emission intensity was enhanced up to 2.6 folds compared to the regular a-plane GaN film. Furthermore, corresponding cathode luminescence images reveal larger emission area for a-plane GaN with annealing than those without annealing, which was attributed to reduction of the nonradiative recombination centers. A series of experiments confirm this annealing process could be useful for further applications of GaN-based optoelectric devices.
Effect of Top-Region Area of Flat-Top Pyramid Patterned Sapphire Substrate on the Optoelectronic Performance of GaN-Based Light-Emitting Diodes
(2016-01-01)
Hsueh, Hsu-Hung
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Ou, Sin-Liang
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Peng, Yu-Che
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Cheng, Chiao-Yang
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Wuu, Dong-Sing
The flat-top pyramid patterned sapphire substrates (FTP-PSSs) have been prepared for the growth of GaN epilayers and the fabrication of lateral-type light-emitting diodes (LEDs) with an emission wavelength of approximately 470 nm. Three kinds of FTP-PSSs, which were denoted as FTP-PSS-A, FTP-PSS-B, and FTP-PSS-C, respectively, were formed through the sequential wet etching processes. The diameters of circle areas on the top regions of these three FTP-PSSs were 1, 2, and 3 mu m, respectively. Based on the X-ray diffraction results, the full-width at half-maximum values of rocking curves at (002) plane for theGaN epilayers grown on conventional sapphire substrate (CSS), FTP-PSS-A, FTP-PSS-B, and FTP-PSS-C were 412, 238, 346, and 357 arcsec, while these values at (102) plane were 593, 327, 352, and 372 arcsec, respectively. The SpeCLED-Ratro simulation results reveal that the LED prepared on FTP-PSS-A has the highest light extraction efficiency than that of the other devices. At an injection current of 350 mA, the output powers of LEDs fabricated on CSS, FTP-PSS-A, FTP-PSS-B, and FTP-PSS-C were 157, 254, 241, and 233 mW, respectively. The results indicate that both the crystal quality of GaN epilayer and the light extraction of LED can be improved via the use of FTP-PSS, especially for the FTP-PSS-A.
Effects of buffer layers and front electrode angles on the performance of In0.16Ga0.84As solar cells
(2016-01-01)
Horng, Ray-Hua
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Wu, Fan-Lei
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Ou, Sin-Liang
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Kao, Yu-Cheng
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Shih, Shan-Hui
Three buffer layers, that included 2-step, step-graded, and linear-graded layers, were designed to improve the performance of In0.16Ga0.84As solar cell. The In0.16Ga0.84As solar cells fabricated on these three buffer layers were denoted as 2S-cell, S-cell, and L-cell, respectively. The efficiencies of these three devices were 9.8%, 14.4%, and 16.3%, respectively. Obviously, the linear-graded buffer layer is most helpful to enhance the efficiency of In0.16Ga0.84As solar cell. Additionally, the front electrode angle of In0.16Ga0.84As solar cell was varied from 0 degrees to 90 degrees. When the angles were fixed at 0 degrees and 90 degrees, the devices possessed higher efficiencies of 16.3% and 16.6%, respectively.
Enhanced Light Extraction of High-Voltage Light Emitting Diodes Using a Sidewall Chamfer Structure
(2017-06-01)
Wu, Ping-Chen
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Ou, Sin-Liang
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Horng, Ray-Hua
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Wuu, Dong-Sing
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電子工程學系及電子研究所
High-voltage light-emitting diodes (HV-LEDs) were prepared with 4 x 2 microcells. A novel technique for enhancing the light extraction of HV-LEDs by using wet-etched chamfer structures in the sidewalls of each cell is proposed. The thicknesses of the u-GaN layers used were in the range of 3-7 mu m. Simulations revealed that the light extraction of the HV-LEDs with chamfer structures would be enhanced by increasing the u-GaN thickness. The output power (@ 80 mA) of the HV-LEDs without chamfer structures was 538.0-539.1 mW. However, the output powers (@ 80 mA) of the HV-LEDs with chamfer structures and u-GaN thicknesses of 3, 5, and 7 mu m were increased to 555.3, 573.1, and 561.6 mW, respectively. The 7 mu m thick u-GaN layer led to an extremely large thickness of the HV-LED epitaxial structure, which caused difficulties during the wet etching process. Because of the apparent decrease in the wet etching rate of GaN, the damages to the epitaxial structures of the HV-LED with the 7 mu m thick u-GaN was more obvious. Therefore, the device's light extraction was slightly reduced. The results confirm that chamfer structures are highly useful for improving the performance of HV-LEDs, especially for the u-GaN thickness of 5 mu m.
Epitaxial Growth of ZnGa2O4: A New, Deep Ultraviolet Semiconductor Candidate
(2017-11-01)
Huang, Ray-Hua
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Huang, Chiung-Yi
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Ou, Sin-Liang
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Juang, Tzu-Kuang
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Liu, Po-Liang
ZnGaO films were grown on c-plane sapphire substrates by metal organic chemical vapor deposition using diethylzinc (DEZn), triethylgallium (TEGa), and oxygen. The flow rate of DEZn was 10-60 sccm, and those of TEGa and oxygen were held constant. The ZnGaO film prepared at a DEZn flow rate of 10 sccm adopted a ((2) over bar 01)-oriented single-crystalline beta-Ga2O3 phase, whereas those prepared at 30-60 sccm exhibited a (111)-oriented single-crystalline ZnGa2O4 phase. On the basis of Hall measurements, ZnGaO films (10 sccm DEZn) possessed very poor electrical properties, which were similar to those of beta-Ga2O3. On the other hand, the carrier concentration in ZnGaO films increased from 1.94 X 10(14) to 6.72 X 10(16) cm(-3), and the resistivity decreased from 5730 to 67.9 Omega-cm when increasing the DEZn flow rate from 30 to 60 sccm. According to compositional analyses, the improved electrical properties of ZnGaO films upon increasing DEZn flow rate from 30 to 40 sccm are due to the increasing Zn content, and the enhancement from 50 to 60 sccm could be due to increased C content. Cathodoluminescence results also confirm the ZnGa2O4 structure for ZnGaO films prepared at DEZn flow rates of 30-60 sccm and reveal their use for ultraviolet applications.
Fabrication of nitride LEDs using chemical lift-off from a GaN/sapphire template
(2016)
Horng, Ray-Hua
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Hsueh, Hsu-Hung
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Ou, Sin-Liang
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Wuu, Dong-Sing
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電子工程學系及電子研究所
Ge/Al bilayer thin film for optical write-once media
(2007-01-01)
Wu, T. H.
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Kuo, P. C.
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Chen, Jung-Po
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Wu, Chih-Yuan
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Yen, Po-Fu
Ge/Al bilayer thin films are prepared by magnetron sputtering. Thermal analysis shows that the phase change of the film occurs at 275 degrees C. Contrasts at 650 rim and 405 nm wavelength are 71.4% and 31.1% respectively.
Improved Performance and Heat Dissipation of Flip-Chip White High-Voltage Light Emitting Diodes
(2017-03)
Wu, Ping-Chen
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Ou, Sin-Liang
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Horng, Ray-Hua
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Wuu, Dong-Sing
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電子工程學系及電子研究所
Three types of white light emitting diodes (LEDs) were constructed with 4 x 1 micro-cells. The first one is the convectional LED series connected with four cells using the wire-bonding process. The other two devices are 4 x 1 lateral-type and 4 x 1 flip-chip high-voltage LEDs (HV-LEDs) using the interconnection technique. The convectional LED, lateral-type HV-LED, and flip-chip HV-LED are denoted as C-LED, L-HV-LED, and FC-HV-LED, respectively. Moreover, the white LEDs were formed by combining the blue LED chips and the phosphor-dispensing method. The thermal resistances (at 20 mA) of C-LED, L-HV-LED, and FC-HV-LED were 14.5, 59.2, and 12.2 K/W, respectively. In addition, the surface temperatures (at 20 mA) of these three devices were 30.74-31.82, 65.93-68.95, and 27.01-27.96 degrees C, respectively. Obviously, the heat dissipation of L-HV-LED was much worse than that of C-LED. However, via the fabrication of the flip-chip structure, the heat dissipation of HV-LED can be enhanced significantly. At an injection current of 100 mA, the luminous efficiencies of C-LED, L-HV-LED, and FC-HV-LED were 80.8, 81.0, and 91.8 lm/W, respectively. Furthermore, at the same forward voltage, a higher current can be driven in the FC-HV-LED, leading to an apparent improvement in the luminous efficiency. According to our calculation, the emission size of HV-LED was only 84% compared with that of C-LED. On the other hand, the fabrication of HV-LED can be performed without the wire-bonding process. This indicates that the FC-HV-LED possesses not only lower production costs but also higher optoelectronic performance than that of the C-LED.
Improved Performance of High-Voltage Vertical GaN LEDs via Modification of Micro-Cell Geometry
(2017-06-01)
Wu, Ping-Chen
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Ou, Sin-Liang
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Horng, Ray-Hua
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Wuu, Dong-Sing
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電子工程學系及電子研究所
Vertical-type high-voltage light-emitting diodes (HV-LEDs) with 2 x 2 micro-cells were fabricated on Cu substrates, and the micro-cell geometry was modified to enhance the optoelectronic performance. The current spreading in micro-cell is most dominantly affected by the distance between electrode and edge of chip. When square cells were combined in a HV-LED, the device performance was poor due to an obvious current-crowding phenomenon that occurred near the electrodes. This was attributed that the electrodes in these four square micro-cells were all far away from the edges, resulting in the severe current-crowding phenomenon. On the contrary, as the HV-LED was prepared with four rectangle, triangle, or L-shaped micro-cells, the electrodes were close to the edges of micro-cells and the current spreading effect can be easily improved. Although a HV-LED connected with L-shaped cells possessed a better current spreading effect and a lower surface temperature, the light extraction was relatively low because of an electrode-shading loss effect. When triangular cells were used to prepare the HV-LED, the device achieved a superior optoelectronic performance compared with that of other cells because of a lower current-crowding effect and a more uniform light emission. After an epoxy package process, a lower forward voltage of 14.9 V and a higher output power of 353.2 mW were obtained using this HV-LED at an injection current of 80 mA. Additionally, the wall-plug efficiencies of this device at 20 and 80 mA were 41.1% and 29.7%, respectively. The results confirm that the design of triangular cell is beneficial for enhancing the optoelectronic performance of HV-LEDs. Furthermore, the fabrication processes of vertical LEDs have high potential for HV-LED applications.
Large-area, uniform white light LED source on a flexible substrate
(2015-09-21)
Sher, Chin-Wei
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Chen, Kuo-Ju
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Lin, Chien-Chung
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Han, Hau-Vei
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Lin, Huang-Yu
This study demonstrates the flexible white LED structure with high lumen efficiency and uniform optical performance for neutral white and warm white CCT. Flip-chip LEDs were attached on a polyimide substrate with copper strips as electrical and thermal conduction paths. Yellow phosphors are mixed with polydimenthysiloxane (PDMS) to provide mechanical support and flexibility. The light efficiency of this device can reach 120 lm/W and 85% of light output uniformity of the emission area can be achieved. Moreover, the optical simulation is employed to evaluate various designs of this flexible film in order to obtain uniform output. Both the pitch between the individual devices and the thickness of the phosphor film are calculated for optimization purpose. This flexible white LED with high lumen efficiency and good reliability is suitable for the large area fixture in the general lighting applications. (C) 2015 Optical Society of America
Performance enhancement of III-V multi-junction solar cells using indium-tin-oxide electrodes
(2016-08-01)
Kao, Yu-Cheng
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Ou, Sin-Liang
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Wu, Fan-Lei
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Horng, Ray-Hua
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電機學院
InGaP/GaAs dual-junction solar cells were prepared on p-type GaAs substrates by metalorganic chemical vapor deposition. Three types of front-side electrodes, which included AuGe/Au metal-finger, ITO-finger, and ITO-overcoated, were individually fabricated on the devices and denoted as samples A, B, and C, respectively. The thickness of ITO film is 200 nm, and its transmittance can reach 99% in the visible region. Based on the current density-voltage (J-V) measurement, the short-circuit current density (J(sc)) of samples A, B, and C are 8.13, 9.35, and 10.90 mA/cm(2), while the conversion efficiencies of these three samples are evaluated to be 15.45%, 18.14%, and 20.24%, respectively. This reveals that sample C possesses 31.0% enhancement in the conversion efficiency compared to that of sample A. Additionally, the series resistances (Rs) of samples A, B, and C are 21.43, 22.94, and 6.71 Omega-cm(2), respectively. The lowest Rs occurred in sample C can be attributed to the elimination of the lateral resistance between electrodes because this device was fabricated with the ITO-overcoated front-side electrode. In sample C, since the ITO front-side electrode can cover overall surface of the device, all regions on the sample surface can extract the electrons, leading to the highest J(sc). (C) 2016 Elsevier B.V. All rights reserved.
Performance of GaN-based light-emitting diodes fabricated using GaN epilayers grown on silicon substrates
(2014-01-13)
Horng, Ray-Hua
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Wu, Bing-Rui
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Tien, Ching-Ho
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Ou, Sin-Liang
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Yang, Min-Hao
Light extraction of GaN-based light-emitting diodes grown on Si(111) substrate (GaN-on-Si based LEDs) is presented in this study. Three different designs of GaN-on-Si based LEDs with the lateral structure, lateral structure on mirror/Si(100) substrate, and vertical structure on mirror/Si(100) substrate were epitaxially grown by metalorganic chemical vapor deposition and fabricated using chemical lift-off and double-transfer techniques. Current-voltage, light output power, far-field radiation patterns, and electroluminescence characteristics of these three LEDs were discussed. At an injection current of 700 mA, the output powers of LEDs with the lateral structure on mirror/Si(100) substrate and vertical structure on mirror/Si(100) substrate were measured to be 155.07 and 261.07 mW, respectively. The output powers of these two LEDs had 70.63% and 187.26% enhancement compared to that of LED with the lateral structure, respectively. The result indicated this vertical structure LED was useful in improving the light extraction due to an enhancement in light scattering efficiency while the high-reflection mirror and diffuse surfaces were employed. (C) 2014 Optical Society of America
Perovskite CsPbBr3 Quantum Dots Prepared Using Discarded Lead-Acid Battery Recycled Waste
(2019-03-02)
Chen, Lung-Chien
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Tien, Ching-Ho
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Ou, Sin-Liang
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Lee, Kun-Yi
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Tian, Jianjun
Perovskite CsPbBr3 quantum dot (CsPbBr3-QD) recovery was performed using lead scrap from lead storage batteries. The perovskite CsPbBr3-QD characteristics were analyzed using different PbO/recycled PbO2 ratios. Scanning electron microscopy (SEM) was used to observe the film surface morphology and cross-section. High-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) were used to observe the perovskite CsPbBr3-QDs' structural characteristics. A photoluminescence (PL) measurement system was used to analyze the optical properties. The results show that lead scrap from lead-acid batteries as a material for perovskite CsPbBr3-QD production can be successfully synthesized. This saves material and also proves that recycling is valuable. The proposed approach is helpful for future material shortages and materials not easily accessible. Although the efficiency is not very high, this process will be purified using recycled lead in the future to achieve higher quantum yield.
Structural and Stress Properties of A1GaN Epilayers Grown on A1N-Nanopatterned Sapphire Templates by Hydride Vapor Phase Epitaxy
(2018-09-01)
Tasi, Chi-Tsung
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Wang, Wei-Kai
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Ou, Sin-Liang
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Huang, Shih-Yung
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Horng, Ray-Hua
In this paper, we report the epitaxial growth and material characteristics of AlGaN (Al mole fraction of 10%) on an AlN/nanopatterned sapphire substrate (NPSS) template by hydride vapor phase epitaxy (HYPE). The crystalline quality, surface morphology, microstructure, and stress state of the AlGaN/AlN/NPSS epilayers were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The results indicate that the crystal quality of the A1GaN film could be improved when grown on the A1N/NPSS template. The screw threading dislocation (TD) density was reduced to 1.4 x 10(9) cm(-2) for the AlGaN epilayer grown on the A1N/NPSS template, which was lower than that of the sample grown on a flat c-plane sapphire substrate (6.3 x 10(9) cm(-2)). As examined by XRD measurements, the biaxial tensile stress of the AlGaN film was significantly reduced from 1,187 MPa (on A1N/NPSS) to 38.41 MPa (on flat c-plane sapphire). In particular, an increase of the Al content in the overgrown AlGaN layer was confirmed by the TEM observation. This could be due to the relaxation of the in-plane stress through the AlGaN and AlN/NPSS template interface.
Surface evolution and effect of V/III ratio modulation on etch-pit-density improvement of thin AlN templates on nano-patterned sapphire substrates by metalorganic chemical vapor deposition
(2018-10-15)
Wang, Tzu-Yu
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Tasi, Chi-Tsung
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Lin, Ku-Yen
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Ou, Sin-Liang
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Horng, Ray-Hua
A low defect-density AlN template film using V/III ratio modulation and nano-patterned sapphire substrate (NPSS) was achieved by metalorganic chemical vapor deposition. In contrast to conventional high-quality AlN/NPSS obtained with high coalescence thickness ( > 6 mu m) using high growth temperatures ( >= 1250 degrees C), this study reveals the high crystallinity of AlN with the lower thickness of 2.55 mu m grown under a lower temperature of 1130 degrees C. It could effectively increase the heater lifetime and reduce the epi-wafer warpage. The growth of AlN/NPSS dominated by epitaxial lateral overgrowth achieves a dramatic reduction of full width at half maximum values along (10 (1) over bar2) plane from 1640 to 714 arcsec, and lowest dislocation density of approximately 1 x 10(8) cm(-2), as well as a ultra-low etching pit density of 2.3 x 10(5) cm(-2). The crack-free AlN/NPSS with a compressive stress owing to the tensile stress was relaxed by the existence of some key-shaped holes upon the patterned region. Details of the surface evolution, mechanism and dislocation behavior of AlN/NPSS will be discussed and these results demonstrate this low-defect template technique of high potential for AlGaN-based device applications.
Tunability of p- and n-channel TiOx thin film transistors
(2018-06-18)
Peng, Wu-Chang
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Chen, Yao-Ching
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He, Ju-Liang
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Ou, Sin-Liang
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Horng, Ray-Hua
To acquire device-quality TiOx films usually needs high-temperature growth or additional post-thermal treatment. However, both processes make it very difficult to form the p-type TiOx even under oxygen-poor growth condition. With the aid of high energy generated by high power impulse magnetron sputtering (HIPIMS), a highly stable p-type TiOx film with good quality can be achieved. In this research, by varying the oxygen flow rate, p-type-gamma-TiO and n-type TiO2 films were both prepared by HIPIMS. Furthermore, p- and n-type thin film transistors employing-gamma-TiO and TiO2 as channel layers possess the field-effect carrier mobilities of 0.2 and 0.7 cm(2)/Vs, while their on/off current ratios are 1.7 x 10(4) and 2.5 x 10(5), respectively. The first presented p-type-gamma-TiO TFT is a major breakthrough for fabricating the TiOx based p-n combinational devices. Additionally, our work also confirms HIPIMS offers the possibility of growing both p- and n-type conductive oxides, significantly expanding the practical usage of this technique.