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High-Bandwidth Green Semipolar (20-21) InGaN/GaN Micro Light-Emitting Diodes for Visible Light Communication
(2020-08-19)
Chen, Sung-Wen Huang
;
Huang, Yu-Ming
;
Chang, Yun-Han
;
Lin, Yue
;
Liou, Fang-Jyun
The light-emitting diode (LED) is among promising candidates of light sources in visible light communication (VLC); however, strong internal polarization fields in common c-plane LEDs, especially green LEDs, result in low frequency and limited transmission performance. This study aims to overcome the limited 3-dB bandwidth of long-wavelength InGaN/GaN LEDs. Thus, semipolar (20-21) micro-LEDs (mu LEDs) were fabricated through several improved approaches on epitaxy and chip processes. The mu LED exhibits a 525 nm peak wavelength and good polarization performance. The highest 3-dB bandwidth up to 756 MHz and 1.5 Gbit/s data rate was achieved under a current density of 2.0 kA/cm(2). These results suggest a good transmission capacity of green semipolar (20-21) mu LEDs in VLC applications.
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
;
Lin, Po-Jung
;
Horng, Ray-Hua
;
Wuu, Dong-Sing
;
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.
Effect of Thermal Management on the Performance of VCSELs
(2020-09-01)
Pan, Po-Chou
;
Nag, Dhiman
;
Khan, Zuhaib
;
Chen, Ching-Jung
;
Shi, Jin-Wei
This study investigated the effect of thermal management on the performance of vertical-cavity surface-emitting lasers (VCSELs). It was found that the thickness of silicon substrate, which can serve as the submount for VCSEL packages, has a strong influence on the thermal dissipation of on-chip laser sources, and eventually impacts on their output characteristics. Moreover, the improvements in optical characteristics of the on-chip VCSELs were the best heat dissipation through thinning silicon substrates to 50-mu m thickness combined with electroplated Cu with 100-mu m thickness. In addition, this study also performed COMSOL simulations. The simulation results were consistent with experimental results.
High-power and single-mode VCSEL arrays with single-polarized outputs by using package-induced tensile strain
(2020-09-01)
Shi, Jin-Wei
;
Khan, Zuhaib
;
Horng, Ray-Hua
;
Yeh, Hsiao-Yun
;
Huang, Chun-Kai
In this work, we demonstrate a novel high-power vertical-cavity surface-emitting laser (VCSEL) array with highly single-mode (SM) and single-polarized output performance without significantly increasing the intra-cavity loss and threshold current (Ith). By combining a low-loss zinc-diffusion aperture with an electroplated copper substrate, we can obtain a highly SM output (side mode suppression ratio >50 dB) with a wry narrow divergence angle (1 / e(2) : similar to 10 degrees) under high output power (3.1 W; 1% duty cycle) and sustain a single polarization state, with a polarization suppression ratio of around 9 dB, under the full range of bias currents. Compared to the reference device without the copper substrate, the demonstrated array can not only switch the output optical spectra from quasi-SM to highly SM but also maintain a close threshold current value (Ith: 0.8 versus 0.7 mA per unit device) and slope efficiency. The enhancement in fundamental mode selectivity of our VCSEL structure can be attributed to the single-polarized lasing mode induced by tensile strain, which is caused by the electroplated copper substrate, as verified by the double-crystal x-ray measurement results. (C) 2020 Optical Society of America
Feasibility Study for Double Luminescent Down-shifting Effect in A Dual Junction Solar Cell
(2019-01-01)
Huang, Yu-Ming
;
Cho, Yu-Yun
;
Hsu, Shun-Chieh
;
Kao, Sheng-Feng
;
Shih, Hsiang-Yun
In this work, we discuss the feasibility of two color photons for boosting up the short-circuit current and power conversion efficiency in tandem solar cell. One of them is by luminescent down-shifting (LDS) effect, and the other one is the infrared light emitting diode at 820nm. The CdZnSeS/ZnS quantum dots are used in this study. It can convert ultra-violet photons to visible ones which could be efficiently transformed into electron-hole pairs. The infrared-radiation LED can increase photo-generated carriers of the bottom GaAs solar cell. Finally, short-circuit current would significantly increase from 10.46 mA/cm(2) to 13.81 mA/cm(2), and power conversion efficiency increase from 19.89 to 25.22%. This result shows the possible double-LDS effect for solar cell enhancement in the future.
Electrical and optical properties of degenerate and semi-insulating ZnGa2O4: Electron/phonon scattering elucidated by quantum magnetoconductivity
(2020-06-22)
Look, David C.
;
Leedy, Kevin D.
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Horng, Ray-Hua
;
Santia, Marco D.
;
Badescu, Stefan C.
We study the electrical and optical properties of degenerate ZnGa2O4 films grown by metalorganic chemical vapor deposition (MOCVD) on sapphire and semi-insulating films grown by pulsed laser deposition (PLD) on fused silica. After a forming-gas anneal at 700 degrees C, the MOCVD film is highly conducting, with a room-temperature carrier concentration of 2 x 10(20)cm(-3), a mobility of 20cm(2)/V s, and direct bandgap absorptions at 3.65eV and 4.60eV. Under the same annealing conditions, the PLD film is semi-insulating, with a direct bandgap absorption at 5.25eV. The phonon structure, important for electrical and thermal conduction as well as superconductivity and other quantum phenomena, is very complicated due to the large number of atoms (and, thus, phonon branches) in the unit cell. However, we show that the phonon contributions to electron mobility (mu(ph)) can be directly measured by quantum-based magnetoconductivity over the temperature span T=10-200 K. From an approximate analytical formula, mu(ph) = function (T-ph, T), we calculate an effective phonon energy kT(ph)(T) that takes account of all phonon contributions at temperature T. For T=10-200K, the value of kT(ph) ranges from about 10 to 90meV, consistent with the energy range of the ZnGa2O4 phonon density of states (at 0K) calculated by density functional theory. The total measured mobility can then be modeled by mu(-1)(tot) = mu(-1)(ii) + mu(-1)(ph), where mu(ii) is the mobility due to ionized-impurity scattering. With a high bandgap, controllable conductivity, high breakdown voltage, and bulk-growth capability, ZnGa2O4 offers opportunities for high-power electronics and UV detectors. Published under license by AIP Publishing.
Process Integration and Interconnection Design of Passive-Matrix LED Micro-Displays With 256 Pixel-Per-Inch Resolution
(2020-01-01)
Yuan, Shuo-Huang
;
Yan, Shih-Siang
;
Yao, Yu-Shiuan
;
Wu, Chung-Cheng
;
Horng, Ray-Hua
A 0.28-inch InGaN-based blue micro-LED display with 256 pixel-per-inch resolution and a pitch of $100 mu m was successfully fabricated in this study. A thick Ti/Al/Ti/Au interconnection metal was deposited on the n-type gallium nitride (n-GaN) region to reduce the interconnection resistance. The micro-LED array with interconnection metal exhibits better electrical property consistency as compared with that of the traditional one. The output power, forward voltage, and external quantum efficiency of micro-LED, which measured under 1-mA current injection with the full lighting mode, are 0.8 mW, 3.0 V, and 10%, respectively. This technique has the potential to integrate InGaN-based LEDs with quantum dots for full-color applications.
Thermal Management of GaN-on-Si High Electron Mobility Transistor by Copper Filled Micro-Trench Structure
(2019-12-23)
Mohanty, Srikant Kumar
;
Chen, Yu-Yan
;
Yeh, Ping-Hung
;
Horng, Ray-Hua
;
交大名義發表
Self-heating effect is a major limitation in achieving the full performance potential of high power GaN power devices. In this work, we reported a micro-trench structure fabricated on the silicon substrate of an AlGaN/GaN high electron mobility transistor (HEMT) via deep reactive ion etching, which was subsequently filled with high thermal conductive material, copper using the electroplating process. From the current-voltage characteristics, the saturation drain current was improved by approximately 17% with the copper filled micro-trench structure due to efficient heat dissipation. The I-DS difference between the pulse and DC bias measurement was about 21% at high bias V-DS due to the self-heating effect. In contrast, the difference was reduced to approximately 8% for the devices with the implementation of the proposed structure. Using Micro-Raman thermometry, we showed that temperature near the drain edge of the channel can be lowered by approximately similar to 22 degrees C in a HEMT operating at similar to 10.6 Wmm(-1) after the implementation of the trench structure. An effective method for the improvement of thermal management to enhance the performance of GaN-on-Silicon HEMTs was demonstrated.
Comparison of Properties of Thin Film AlGaInP LEDs with Composite Metal and Si Substrates
(2019-11-25)
Sinha, ShreeKant
;
Feng, Hsiang-An
;
Chung, Cheng-Yu
;
Tu, Chia-Wei
;
Horng, Ray-Hua
N-side up thin-AlGaInP epilayers based on vertical light-emitting diodes (VLEDs) (light emitting area: 44 mil x 44 mil) with Si and composite metal (copper/Invar/copper; CIC) substrates were obtained by wafer bonding and epilayer transferring technologies. The coefficients of thermal expansion of the Si and CIC substrates were about 2.6 x 10(-6) /K and 6.1 x 10(-6) /K respectively. The coefficient of thermal expansion of CIC was matched to the GaAs substrate and AlGaInP epilayer. After the epilayer transferred to the CIC substrate, a small amount of bending occurred. The performance of the packaged LEDs/CIC was almost the same with that of LEDs/Si. The redshift phenomenon was from 623 to 643 nm for the CIC/LEDs while that of the LEDs/Si chip was from 625 to 643 nm with an injected current from 100 mA to 1 A and high output power (251 mW at 1 A) as compared to packaged LEDs/Si (299.5 mW at 1 A). The variation in light-emitting wavelengths of the LEDs/CIC was the same with that of the LEDs/Si. The distribution of the temperature of the LEDs on the CIC substrate was less than the LEDs on Si throughout the surface. The obtained data suggested that CIC could be extended instead of a Si substrate for high-power thin film LEDs applications. (c) The Author(s) 2019. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited.
An efficient and stable photoelectrochemical system with 9% solar-to-hydrogen conversion efficiency via InGaP/GaAs double junction
(2019-11-21)
Varadhan, Purushothaman
;
Fu, Hui-Chun
;
Kao, Yu-Cheng
;
Horng, Ray-Hua
;
He, Jr-Hau
Despite III-V semiconductors demonstrating extraordinary solar-to-hydrogen (STH) conversion efficiencies, high cost and poor stability greatly impede their practical implementation in photoelectrochemical (PEC) water splitting applications. Here, we present a simple and efficient strategy for III-V-based photoelectrodes that functionally and spatially decouples the light harvesting component of the device from the electrolysis part that eliminates parasitic light absorption, reduces the cost, and enhances the stability without any compromise in efficiency. The monolithically integrated PEC cell was fabricated by an epitaxial lift-off and transfer of inversely grown InGaP/GaAs to a robust Ni-substrate and the resultant photoanode exhibits an STH efficiency of similar to 9% with stability similar to 150 h. Moreover, with the ability to access both sides of the device, we constructed a fully-integrated, unassisted-wireless "artificial leaf" system with an STH efficiency of similar to 6%. The excellent efficiency and stability achieved herein are attributed to the light harvesting/catalysis decoupling scheme, which concurrently improves the optical, electrical, and electrocatalytic characteristics.

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