Browsing by Author "Wuu, Dong-Sing"

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A New Material and Structures for Light-Emitting Thyristor Applications
(2018-07-01)
Chen, Ching-Ho
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Jhen, Jia-Jhen
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Wuu, Dong-Sing
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Horng, Ray-Hua
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電子工程學系及電子研究所
We have demonstrated that GaInP materials with GaP and distributed Bragg reflector (DBR) structures can be applied in light-emitting thyristors (LEThs) and depleted optical thyristors (DOTs). The GaP epitaxial film greatly improved the current spreading, so that the brightness of LEThs was also greatly improved. The luminous intensity increased by 70% at an injection current of 250 mA with the GaP epitaxial film, compared to the LEThs without a GaP film. Moreover, the DBR structure played a role to prevent the emission light from being absorbed by the opaque GaAs substrate. The DBR structure can improve the droop efficiency, reduce the operation voltage, and maintain the wavelength at high-current operation. The luminous intensity of LEThs with the 18-pairs DBR structure increased by 71% at an injection current of 900 mA, compared to LETh with only three-pairs DBR and GaP window structure. It also showed nonlinear s-shaped I-V characteristics as a function of the input light intensity. The turn-on voltages were significantly reduced, from 5.36 to 1.66 V, as the external optical input intensity changed from dark to light with 300 mW. Under certain conditions, it also showed standard diode curve characteristics; as a result, the LETh can also be used as a DOTs.
AlGaN/GaN MOS-HEMTs with Corona-Discharge Plasma Treatment
(2017-05-01)
Yuan, Shuo-Huang
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Chang, Feng-Yeh
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Wuu, Dong-Sing
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Horng, Ray-Hua
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電子工程學系及電子研究所
The effects of a corona-discharge plasma treatment on the performance of an AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistor fabricated onto Si substrates were studied. The threshold voltage shifted from -8.15 to -4.21 V when the device was treated with an Al2O3 layer. The leakage current was reduced from 2.9 x 10(-5) to 4.2 x 10(-7) mA/mm, and the I-ON/I-OFF ratio increased from 8.3 x 10(6) to 7.3 x 10(8) using the corona-discharge plasma treatment, which exhibited an increase of about two orders of magnitude. The device exhibited excellent performance with a subthreshold swing of 78 mV/dec and a peak gain of 47.92 mS/mm at V-GS = 10 V.
Characteristics of atomic layer deposition-grown zinc oxide thin film with and without aluminum
(2019-10-15)
Tseng, Ming-Chun
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Wuu, Dong-Sing
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Chen, Chi-Lu
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Lee, Hsin-Ying
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Chien, Cheng-Yu
Zinc oxide (ZnO) and Al-doped ZnO (AZO) thin films were deposited on glass substrates using atomic layer deposition. The Al composition of the AZO thin films was varied by controlling the Zn:Al cycle ratios. The ZnO and AZO thin films were characterized using atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and optical measurements. The electrical properties of the ZnO and AZO thin films were influenced by the Zn:Al cycle ratios. The resistivity of the AZO thin film decreased significantly, whereas the carrier concentration increased with the Al composition. As the Zn:Al cycle ratio increased, the AZO thin film achieved an average transmittance of > 85%.
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 the Phosphor Permanent Substrate on the Angular CCT for White Thin-Film Flip-Chip Light-Emitting Diodes
(2016-10)
Tien, Ching-Ho
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Ho, Kuo-Wei
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Chien, Huan-Yu
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Wuu, Dong-Sing
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Horng, Ray-Hua
This paper developed a phosphor layer applied for thin-film flip-chip light-emitting diodes (TFFC-LEDs) to produce uniform phosphor-converted TFFC white LEDs (TFFC-WLEDs) by combination of laser liftoff, secondary transferring, and surface roughening process. The spin-coating method was used for phosphor layer fabrication onto a substrate to form the phosphor permanent substrate. The TFFC-LEDs were then bonded onto the permanent substrate. From the results, the blue TFFC GaN-based LED with roughened u-GaN surface on a glass substrate (TFRG-LED) demonstrated a 54.2% (at 350 mA) enhancement in light output power, compared with a blue flip-chip GaN-on-sapphire based LED. As the TFFC GaN/phosphor-/glass-based white LED with roughened u-GaN surface (TFRG-WLED) was operated at a forward-bias current of 350 mA, the enhancement of luminous flux was increased by 75.5%, compared with a TFFC GaN/phosphor template-/glass-based white LED. The angular correlated color temperature (CCT) deviation of a TFRG-WLED can be reduced to 1279 K in the range from -75 degrees to +75 degrees at 5000-6000 K application. The TFRG-WLED was fabricated on the glass substrate with the roughened u-GaN surface and the structure of phosphor layer closed to the u-GaN. These kinds of FRGB-WLED structure contribute to a better light extraction characteristic and a higher CCT stability.
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.
Enhanced light extraction in wafer-bonded p-side-up thin-film AlGaInP light emitting diodes via zinc oxide nanorods
(2016-10-01)
Tseng, Ming-Chun
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Wuu, Dong-Sing
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Chen, Chi-Lu
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Lee, Hsin-Ying
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Lin, Yu-Chang
ZnO nanorods grown via hydrothermal method on the aluminum-doped zinc oxide (AZO) thin film were used to fabricate high-brightness p-side-up thin-film AlGaInP light-emitting diodes (LEDs). The AZO thin film was not only used as current spreading layers but also as a seed layer of ZnO nanorods. The AZO thin film was prepared using atomic layer deposition. The ZnO nanorods improved light extraction, thus increasing the light output power of the LEDs. The output powers of LEDs with optimum ZnO nanorod structures were increased by 32% at an injection current of 700 mA, as compared with that of an LED with AZO thin film. The emission wavelength shifts of LEDs with an AZO thin film and optimum ZnO nanorod structure were 18 and 11 nm, respectively, when the injection current was increased from 20 to 1000 mA. The ZnO nanorods not only provide more light extraction but also keep the thermal stability of the LED device without any degradation. The results are promising for the developed high brightness AlGaInP LED applications with low fabrication cost through ZnO nanorods grown by hydrothermal method to enhance the light extraction efficiency. (C) 2016 Optical Society of America
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.
Fabrication and characterization of InGaN-based green resonant-cavity LEDs using hydrogen ion-implantation techniques
(2007)
Huang, Shih-Yung
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Horng, Ray-Hua
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Kuo, Hao-Chung
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Wuu, Dong-Sing
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光電工程學系
The InGaN-based green resonant-cavity light-emitting diodes (RCLEDs) have been fabricated using hydrogen ion-implantation and laser liftoff techniques. The RCLEDs structure consisted of an InGaN/GaN multiple-quantum-well active layer between the top (5 pairs) and bottom (7.5 pairs) dielectric TiO2/SiO2 distributed Bragg reflectors with optical reflectance of 85% and 99.9%, respectively. The insulation layers of the RCLEDs with and without H+ implantation were formed by the hydrogen ion-implantation layers of 1x10(14) ions/cm(2) concentration and SiO2 film, respectively. The corresponding forward turn-on voltage at 0.6 kA/cm(2) dc current density injection were about similar to 4.58 V and similar to 4.55 V for the RCLEDs with and without H+ implantation. The light output intensity of the RCLEDs with H+ implantation is higher by a factor of 1.4 as compared to that of the similar structure without H+ implantation at a current density of 0.6 kA/cm(2). The directionality of RCLEDs with H+ implantation is superior to that of RCLEDs without H+ implantation. (c) 2007 The Electrochemical Society.
Fabrication and Study on Red Light Micro-LED Displays
(2018-01-01)
Horng, Ray-Hua
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Chien, Huan-Yu
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Tarntair, Fu-Gow
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Wuu, Dong-Sing
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交大名義發表
A red-light micro LED display made of an AlGaInP epilayer with a resolution of 64 x 32 pixels, a pitch of 175 mu m and a luminous area of 1 cm x 0.5 cm was fabricated and characterized in this study. The AlGaInP epilayer was bonded to double polished sapphire substrate by wafer-bonding technique and then removing the absorbing GaAs substrate. In this design, the ITO was applied as one of the conducting electrodes of the emitting surface, which can be beneficial since the emitting light is not shielded by metal electrodes. The other key process for LED panel fabrication is planarization. Polymer material was used to fill the gap between each pixel, which was used to prevent a short or open circuit using the planarization process. The driving mode of this display is passive multi-electrode addressable controlling. The luminance of this micro-LED panel is more than 450 nits with an operating voltage of 3 V which is three times higher than that of the OLED operating in the same driving mode.
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
Growth characteristics of Fe-doped GaN epilayers on SiC (001) substrates and their effects on high breakdown voltage devices
(2020-11-15)
Chang, Kai-Ping
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Lin, Po-Jung
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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
The growth characteristics of Fe-doped GaN epitaxial layers on semi-insulating SiC (001) substrates were studied using metalorganic chemical vapor deposition for high breakdown voltage device applications. A smooth Fe-doped GaN epilayer surface can be realized by changing the ferrocene flow, while higher Fe concentrations in the GaN epilayer affect the surface morphology. To reduce the Fe trapping carrier and the sheet resistances of the two-dimension electron gas generated from the interface of AlGaN and GaN, the thickness ratio of Fe-doped and undoped GaN bi-epilayers was also optimized. AlGaN/GaN high electron mobility transistors with the optimum doping concentration of Fe-doped GaN and suitable thickness of undoped GaN have been successfully developed. The achieved breakdown voltage of the Fe-doped GaN epitaxial layer can be as high as 2457 V, which is attributed to the Fe-doped GaN epitaxial layer with higher resistance, which can sustain the high breakdown voltage. The details of the correlation between the surface morphology, Fe concentration, and thickness of Fe-doped GaN epitaxial layers used for high breakdown voltage devices will be also discussed in this paper.
High-Performance InGaN-Based Green Resonant-Cavity Light-Emitting Diodes for Plastic Optical Fiber Applications
(2009-09-15)
Huang, Shih-Yung
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Horng, Ray-Hua
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Shi, Jin-Wei
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Kuo, Hao-Chung
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Wuu, Dong-Sing
High-performance InGaN-based green resonant-cavity light-emitting diodes (RCLEDs) with a plating Cu substrate for plastic optical fiber communication applications are reported. Good stability of emission wavelength was obtained at 0.016 nm/mA. The RCLEDs presents low temperature dependence, showing only a 3% drop in light output power as the temperature increasing from 25 to 85 degrees C. The superior performance can be attributed to the decreased dynamic series resistance and the enhanced thermal dissipation of the heat sink substrate.
Improved Optoelectronic Performance of High-Voltage Ultraviolet Light-Emitting Diodes Through Electrode Designs
(2017-11-01)
Tien, Ching-Ho
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Kuo, Chen-Hao
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Wuu, Dong-Sing
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Horng, Ray-Hua
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電子工程學系及電子研究所
High-efficiency high-voltage ultraviolet light-emitting diodes (HV-UVLEDs) consisting of a 4 x 4 microcells array with an area of 61 mil x 33 mil were designed and fabricated via the electrode pattern and interconnect technique. Polymer material was used to fill trench with planarization, and interconnection technology was used for metal layer connection to address wiring defect issue. In comparison with the conventional lateral UV-LED (C-UVLED), which had 33.6% and 34.7% enhancement in the light output power and wall-plug efficiency (at 1.5 W) of the HV-UVLEDs. A 56% improvement in the external quantum efficiency droop behavior was achieved for the HV-UVLEDs when compared with that of C-UVLED. This improvement can be attributed to superior current spreading in the HV-UVLED due to its smaller microcells, which increases light-emission efficiency overall.
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 375 nm InGaN/AlGaN light-emitting diodes by incorporating a heavily Si-doped transition layer
(2012-01-01)
Huang, Shih-Cheng
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Shen, Kun-Ching
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Tu, Po-Min
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Wuu, Dong-Sing
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Kuo, Hao-Chung
High performance 375-nm ultraviolet (UV) InGaN/AlGaN light-emitting diodes (LEDs) was developed using a heavy Si-doping technique with metalorganic chemical vapor deposition (MOCVD). From the transmission electron microcopy (TEM) image, the dislocation density was reduced after inserting a heavily Si-doping growth mode transition layer (GMTL) between un-doped GaN layer and Si-doped Al0.02Ga0.98N contact layer. The internal quantum efficiency (IQE) of the sample with GMTL measured by power-dependent photoluminescence shows 39.4% improved compared with the sample without GMTL. When the vertical type LED chips (size: 1mmx1mm) driving by a 350-mA current, the output powers of the LEDs with and without GMTL were measured to be 286.7 mW and 204.2 mW, respectively. As much as 40.4% increased light output power was achieved. Therefore, using the GMTL to reduce dislocation defects would be a promising prospective for InGaN/AlGaN UV LEDs to achieve high internal quantum efficiency.
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.
Investigation of efficiency droop for InGaN-based UV light-emitting diodes with InAlGaN barrier
(2011-05-23)
Tu, Po-Min
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Chang, Chun-Yen
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Huang, Shih-Cheng
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Chiu, Ching-Hsueh
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Chang, Jet-Rung
The efficiency droop in InGaN-based UV light emitting device (LED) with AlGaN and InAlGaN barrier is investigated. Electroluminescence results indicate that the light performance of quaternary LEDs can be enhanced by 25% and 55% at 350 mA and 1000 mA, respectively. Furthermore, simulations show that quaternary LEDs exhibit 62% higher radiative recombination rate and low efficiency degradation of 13% at a high injection current. We attribute this improvement to increasing of carrier concentration and uniform redistribution of carriers. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3591967]
ITO/nano-Ag Plasmonic Window Applied for Efficiency Improvement of Near-Ultraviolet Light Emitting Diodes
(2016)
Tien, Ching-Ho
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Zhang, Chia-Hao
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Chung, Shih-Hao
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Ou, Shih-Liang
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Horng, Ray-Hua
Ohmic contact behavior of aluminum-doped zinc oxide with carbondoped p-GaP epilayer for AlGaInP LEDs applications
(2017-07-01)
Tseng, Ming-Chun
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Wuu, Dong-Sing
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Chen, Chi-Lu
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Lee, Hsin-Ying
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Horng, Ray-Hua
Aluminum-doped zinc oxide (AZO) thin films used for ohmic contact layers on carbon-doped GaP window layers (p-GaP:C) of AlGaInP light-emitting diodes were fabricated and characterized. AZO thin films with different Zn:Al cycle ratios (15:1, 20:1, and 25:1) were deposited on p-GaP:C window layers through atomic layer deposition. The contact characteristics of the AZO thin films on p-GaP:C were considerably changed from Schottky contact to ohmic contact after rapid thermal annealing (RTA) at 350 degrees C for 1 min. The most favorable specific contact resistance of AZO/p-GaP:C was evaluated using a circular transmission line model as 6.3 x 10(-3) Omega/cm(2). Angle-resolved X-ray photoelectron spectroscopy was employed to understand the ohmic contact behavior of AZO/p-GaP:C. After RTA, Zn atoms in the AZO thin films notably diffused into the p-GaP:C layers and Ga atoms diffused out of the p-GaP:C layer. Therefore, the Ga vacancies were occupied by Zn atoms, which increased the doping concentration in the near-surface region of p-GaP:C and reduced the depletion region width of the semiconductor region. Thus, numerous carriers were able to tunnel through the reduced Schottky barrier and those carriers produced the ohmic contact behavior between the AZO and p-GaP:C. (C) 2017 Elsevier B. V. All rights reserved.