Browsing by Author "He, Jr-Hau"

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4-Gbit/s visible light communication link based on 16-QAM OFDM transmission over remote phosphor-film converted white light by using blue laser diode
(2015-12-28)
Retamal, Jose Ramon Duran
;
Oubei, Hassan Makine
;
Janjua, Bilal
;
Chi, Yu-Chieh
;
Wang, Huai-Yung
Visible Light Communication (VLC) as a new technology for ultrahigh-speed communication is still limited when using slow modulation light-emitting diode (LED). Alternatively, we present a 4-Gbit/s VLC system using coherent blue-laser diode (LD) via 16-quadrature amplitude modulation orthogonal frequency division multiplexing. By changing the composition and the optical-configuration of a remote phosphor-film the generated white light is tuned from cool day to neutral, and the bit error rate is optimized from 1.9 x 10(-2) to 2.8 x 10(-5) in a blue filter-free link due to enhanced blue light transmission in forward direction. Briefly, blue-LD is an alternative to LED for generating white light and boosting the data rate of VLC. (C) 2015 Optical Society of America
4-Gbit/s visible light communication link based on 16-QAM OFDM transmission over remote phosphor-film converted white light by using blue laser diode
(2015-12-28)
Retamal, Jose Ramon Duran
;
Oubei, Hassan Makine
;
Janjua, Bilal
;
Chi, Yu-Chieh
;
Wang, Huai-Yung
Visible Light Communication (VLC) as a new technology for ultrahigh-speed communication is still limited when using slow modulation light-emitting diode (LED). Alternatively, we present a 4-Gbit/s VLC system using coherent blue-laser diode (LD) via 16-quadrature amplitude modulation orthogonal frequency division multiplexing. By changing the composition and the optical-configuration of a remote phosphor-film the generated white light is tuned from cool day to neutral, and the bit error rate is optimized from 1.9 x 10(-2) to 2.8 x 10(-5) in a blue filter-free link due to enhanced blue light transmission in forward direction. Briefly, blue-LD is an alternative to LED for generating white light and boosting the data rate of VLC. (C) 2015 Optical Society of America
4.8 Gbit/s 16-QAM-OFDM transmission based on compact 450-nm laser for underwater wireless optical communication
(2015-09-07)
Oubei, Hassan M.
;
Duran, Jose R.
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Janjua, Bilal
;
Wang, Huai-Yung
;
Tsai, Cheng-Ting
We experimentally demonstrate an underwater wireless optical communications (UWOC) employing 450-nm TO-9 packaged and fiber-pigtailed laser diode (LD) directly encoded with an orthogonal frequency division multiplexed quadrature amplitude modulation (QAM-OFDM) data. A record data rate of up to 4.8 Gbit/s over 5.4-m transmission distance is achieved. By encoding the full 1.2-GHz bandwidth of the 450-nm LD with a 16-QAM-OFDM data, an error vector magnitude (EVM) of 16.5%, a signal-to-noise ratio (SNR) of 15.63 dB and a bit error rate (BER) of 2.6 x 10-3, well pass the forward error correction (FEC) criterion, were obtained. (C) 2015 Optical Society of America
A Nanostructuring Method to Decouple Electrical and Thermal Transport through the Formation of Electrically Triggered Conductive Nanofilaments
(2018-07-12)
Retamal, Jose Ramon Duran
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Kang, Chen-Fang
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Lien, Der-Hsien
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Kuo, Wei-Cheng
;
Juang, Zhen-Yu
Transforming thermal energy into electric energy and vice versa needs the decoupling of electrical transport from thermal transport. An innovative strategy is proposed by forming/disrupting electrically triggered conductive nanofilaments within semiconducting thin films to switch thermoelectric properties between two states without further material modification and manufacturing processes. It can also controllably adjust the degree of decoupling, providing a potential resolution and performance adjustability for heat/coldness control or power consumption reduction on demand.
A ZnO/InN/GaN Heterojunction Photodetector with Extended Infrared Response
(2015)
Hsu, Lung-Hsing
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Hsu, Shun-Chieh
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Lee, Hsin-Ying
;
Tsai, Yu-Lin
;
Lin, Da-Wei
An extended infrared photoresponse is observed in a ZnO/InN/GaN heterojunction diode with InN grown by MOCVD. The external quantum efficiency is measured between 1200 and 1800 nm and can be as high as 3.55%.
An efficient and stable photoelectrochemical system with 9% solar-to-hydrogen conversion efficiency via InGaP/GaAs double junction
(2019-11-21)
Varadhan, Purushothaman
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Fu, Hui-Chun
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Kao, Yu-Cheng
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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.
Band Gap-Tunable Molybdenum Sulfide Selenide Monolayer Alloy
(2014-07-09)
Su, Sheng-Han
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Hsu, Yu-Te
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Chang, Yung-Huang
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Chiu, Ming-Hui
;
Hsu, Chang-Lung
Bridging the "green gap" of LEDs: giant light output enhancement and directional control of LEDs via embedded nano-void photonic crystals
(2016-01-01)
Tsai, Yu-Lin
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Liu, Che-Yu
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Krishnan, Chirenjeevi
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Lin, Da-Wei
;
Chu, You-Chen
Green LEDs do not show the same level of performance as their blue and red cousins, greatly hindering the solid-state lighting development, which is the so-called "green gap". In this work, nano-void photonic crystals (NVPCs) were fabricated to embed within the GaN/InGaN green LEDs by using epitaxial lateral overgrowth (ELO) and nano-sphere lithography techniques. The NVPCs act as an efficient scattering back-reflector to outcouple the guided and downward photons, which not only boost the light extraction efficiency of LEDs with an enhancement of 78% but also collimate the view angle of LEDs from 131.5 degrees to 114.0 degrees. This could be because of the highly scattering nature of NVPCs which reduce the interference giving rise to Fabry-Perot resonance. Moreover, due to the threading dislocation suppression and strain relief by the NVPCs, the internal quantum efficiency was increased by 25% and droop behavior was reduced from 37.4% to 25.9%. The enhancement of light output power can be achieved as high as 151% at a driving current of 350 mA. Giant light output enhancement and directional control via NVPCs point the way towards a promising avenue of solid-state lighting.
Characterizations of low-temperature electroluminescence from ZnO nanowire light-emitting arrays on the p-GaN layer
(2010-12-15)
Lu, Tzu-Chun
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Ke, Min-Yung
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Yang, Sheng-Chieh
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Cheng, Yun-Wei
;
Chen, Liang-Yi
Low-temperature electroluminescence from ZnO nanowire light-emitting arrays is reported. By inserting a thin MgO current blocking layer in between ZnO nanowire and p-GaN, high-purity UV light emission at wavelength 398 nm was obtained. As the temperature is decreased, contrary to the typical GaN-based light emitting diodes, our device shows a decrease of optical output intensity. The results are associated with various carrier tunneling processes and frozen MgO defects. (C) 2010 Optical Society of America
Control of the Metal-Insulator Transition at Complex Oxide Heterointerfaces through Visible Light
(2016-01-27)
Lin, Jheng-Cyuan
;
Vu Thanh Tra
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Tsai, Dung-Sheng
;
Lin, Tai-Te
;
Huang, Po-Cheng
The coupling of the localized surface plasmon resonance of Au nanoparticles is utilized to deliver a visible-light stimulus to control conduction at the LaAlO3/SrTiO3 interface. A giant photoresponse and the controllable metal-insulator transition are characterized at this heterointerface. This study paves a new route to optical control of the functionality at the heterointerfaces.
Electricity generation based on vertically aligned PbZr0.2Ti0.8O3 nanowire arrays
(2012-05-01)
Chen, Cheng-Ying
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Liu, Te-Hsiang
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Zhou, Yusheng
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Zhang, Yan
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Chueh, Yu-Lun
We statistically demonstrated the electricity generation from individual vertically-aligned/epitaxial PbZr0.2Ti0.8O3 (PZT) nanowires (NWs) using a conductive atomic force microscope (AFM). The measured outputs were analyzed in reference to the theoretically calculated piezopotential distribution in a bent NW. Our results show that the performance of the PZT NWs for electricity generation is at the same level as that of ZnO NWs although the piezocoefficient of PZT is high, due to high relative dielectric constant of PZT. Systematic investigating piezoelectricity from single PZT NWs will be useful for optimizing the performance for PZT nanogenerator applications. (C) 2012 Elsevier Ltd. All rights reserved.
Epitaxial growth of a monolayer WSe2-MoS2 lateral p-n junction with an atomically sharp interface
(2015-07-31)
Li, Ming-Yang
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Shi, Yumeng
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Cheng, Chia-Chin
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Lu, Li-Syuan
;
Lin, Yung-Chang
Two-dimensional transition metal dichalcogenides (TMDCs) such as molybdenum sulfide MoS2 and tungsten sulfide WSe2 have potential applications in electronics because they exhibit high on-off current ratios and distinctive electro-optical properties. Spatially connected TMDC lateral heterojunctions are key components for constructing monolayer p-n rectifying diodes, light-emitting diodes, photovoltaic devices, and bipolar junction transistors. However, such structures are not readily prepared via the layer-stacking techniques, and direct growth favors the thermodynamically preferred TMDC alloys. We report the two-step epitaxial growth of lateral WSe2-MoS2 heterojunction, where the edge of WSe2 induces the epitaxial MoS2 growth despite a large lattice mismatch. The epitaxial growth process offers a controllable method to obtain lateral heterojunction with an atomically sharp interface.
Few-Layer MoS2 with High Broadband Photogain and Fast Optical Switching for Use in Harsh Environments
(2013-05-01)
Tsai, Dung-Sheng
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Liu, Keng-Ku
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Lien, Der-Hsien
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Tsai, Meng-Lin
;
Kang, Chen-Fang
Few-layered MoS2 as Schottky metal-semiconductor-metal photodetectors (MSM PDs) for use In harsh environments makes its debut as two-dimensional (2D) optoelectronics with high broadband gain (up to 13.3), high detectivity (up to similar to 10(10) cm Hz(1/2)/W), fast photoresponse (rise time of similar to 70 mu s and fall time of similar to 110 mu s), and high thermal stability (at a working temperature of up to 200 degrees C). Ultrahigh responsivity (0.57 A/W) of few-layer MoS2 at 532 nm is due to the high optical absorption (similar to 10% despite being less than 2 nm in thickness) and a high photogain, which sets up a new record that was not achievable in 2D nanomaterials previously. This study opens avenues to develop 2D nanomaterial-based optoelectronics for harsh environments in imaging techniques and light-wave communications as well as in future memory storage and optoelectronic circuits.
Giant Optical Anisotropy of Perovskite Nanowire Array Films
(1970-01-01)
Lin, Chun-Ho
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Kang, Chieh-Yu
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Wu, Ting-Zhu
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Tsai, Chun-Lin
;
Sher, Chin-Wei
Polarizers play a key role in generating polarized light for display, imaging, and data communication, but adoption often suffers from high optical loss. Recently, due to superior optoelectronic properties, halide perovskites have been widely developed for lighting applications; however, highly polarized emission (polarization degree >0.8) has not yet been realized with perovskites. Herein, by incorporating inkjet printing and an anodic aluminum oxide (AAO) confinement strategy, highly ordered perovskite nanowire (NW) arrays are demonstrated for anisotropic optical applications. The optical device based on perovskite NW arrays reveals a high photoluminescence external quantum efficiency of 21.6% and emits highly polarized light with polarization degree up to 0.84. The highly polarized emission from perovskite NW arrays has potential to considerably reduce the optical loss of polarizers, which may attract great interest in developing polarized light sources for next-generation optoelectronic applications.
Giant Photoresponse in Quantized SrRuO3 Monolayer at Oxide Interfaces
(2018-03-01)
Liu, Heng-Jui
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Wang, Jing-Ching
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Cho, Deok-Yong
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Ho, Kang-Ting
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Lin, Jheng-Cyuan
The photoelectric effect in semiconductors is the main mechanism for most modern optoelectronic devices, in which the adequate bandgap plays the key role for acquiring high photoresponse. Among numerous material categories applied in this field, the complex oxides exhibit great possibilities because they present a wide distribution of band gaps for absorbing light with any wavelength. Their physical properties and lattice structures are always strongly coupled and sensitive to light illumination. Moreover, the confinement of dimensionality of the complex oxides in the heterostructures can provide more diversities in designing and modulating the band structures. On the basis of this perspective, we have chosen itinerary ferromagnetic SrRuO3 as the model material, and fabricated it in one-unit-cell thickness in order to open a small band gap for effective utilization of visible light. By inserting this SrRuO3 monolayer at the interface of the well-developed two-dimensional electron gas system (LaAlO3/SrTiO3), the resistance of the monolayer can be further revealed. In addition, a giant enhancement (>300%) of photoresponse under illumination of visible light with power density of 500 mW/cm(2) is also observed. Such can be ascribed to the further modulation of band structure of the SrRuO3 monolayer under the illumination, confirmed by cross-section scanning tunneling microscopy (XSTM). Therefore, this study demonstrates a simple route to design and explore the potential low dimensional oxide materials for future optoelectronic devices.
Going beyond 4 Gbps data rate by employing RGB laser diodes for visible light communication
(2015-07-13)
Janjua, Bilal
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Oubei, Hassan M.
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Retamal, Jose R. Duran
;
Ng, Tien Khee
;
Tsai, Cheng-Ting
With increasing interest in visible light communication, the laser diode (LD) provides an attractive alternative, with higher efficiency, shorter linewidth and larger bandwidth for high-speed visible light communication (VLC). Previously, more than 3 Gbps data rate was demonstrated using LED. By using LDs and spectral-efficient orthogonal frequency division multiplexing encoding scheme, significantly higher data rates has been achieved in this work. Using 16-QAM modulation scheme, in conjunction with red, blue and green LDs, data rates of 4.4 Gbps, 4 Gbps and 4 Gbps, with the corresponding BER/SNR/EVM of 3.3 x 10(-3)/15.3/17.9, 1.4 x 10-3/16.3/15.4 and 2.8 x 10(-3)/15.5/16.7 were obtained over transmission distance of similar to 20 cm. We also simultaneously demonstrated white light emission using red, blue and green LDs, after passing through a commercially available diffuser element. Our work highlighted that a tradeoff exists in operating the blue LDs at optimum bias condition while maintaining good color temperature. The best results were obtained when encoding red LDs which gave both the strongest received signal amplitude and white light with CCT value of 5835K. (C) 2015 Optical Society of America
In Situ TEM and Energy Dispersion Spectrometer Analysis of Chemical Composition Change in ZnO Nanowire Resistive Memories
(2013-04-16)
Huang, Yu-Ting
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Yu, Shih-Ying
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Hsin, Cheng-Lun
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Huang, Chun-Wei
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Kang, Chen-Fang
Resistive random-access memory (ReRAM) has been of wide interest for its potential to replace flash memory in the next-generation nonvolatile memory roadmap. In this study, we have fabricated the Au/ZnO-nanowire/Au nanomemory device by electron beam lithography and, subsequently, utilized in situ transmission electron microscopy (TEM) to observe the atomic structure evolution from the initial state to the low-resistance state (LRS) in the ZnO nanowire. The element mapping of LRS showing that the nanowire was zinc dominant indicating that the oxygen vacancies were introduced after resistance switching. The results provided direct evidence, suggesting that the resistance change resulted from oxygen migration.
InN-based heterojunction photodetector with extended infrared response
(2015-11-30)
Hsu, Lung-Hsing
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Kuo, Chien-Ting
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Huang, Jhih-Kai
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Hsu, Shun-Chieh
;
Lee, Hsin-Ying
The combination of ZnO, InN, and GaN epitaxial layers is explored to provide long wavelength photodetection capability in the GaN based materials. Growth temperature optimization was performed to obtain the best quality of InN epitaxial layer in the MOCVD system. The temperature dependent photoluminescence (PL) can provide the information about thermal quenching in the InN PL transitions and at least two non-radiative processes can be observed. X-ray diffraction and energy dispersive spectroscopy are applied to confirm the inclusion of indium and the formation of InN layer. The band alignment of such system shows a typical double heterojunction, which is preferred in optoelectronic device operation. The photodetector manufactured by this ZnO/GaN/InN layer can exhibit extended long-wavelength quantum efficiency, as high as 3.55%, and very strong photocurrent response under solar simulator illumination. (C) 2015 Optical Society of America
Micro-light-emitting diodes with quantum dots in display technology
(2020-05-11)
Liu, Zhaojun
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Lin, Chun-Ho
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Hyun, Byung-Ryool
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Sher, Chin-Wei
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Lv, Zhijian
Micro-light-emitting diodes (mu-LEDs) are regarded as the cornerstone of next-generation display technology to meet the personalised demands of advanced applications, such as mobile phones, wearable watches, virtual/augmented reality, micro-projectors and ultrahigh-definition TVs. However, as the LED chip size shrinks to below 20 mu m, conventional phosphor colour conversion cannot present sufficient luminance and yield to support high-resolution displays due to the low absorption cross-section. The emergence of quantum dot (QD) materials is expected to fill this gap due to their remarkable photoluminescence, narrow bandwidth emission, colour tuneability, high quantum yield and nanoscale size, providing a powerful full-colour solution for mu-LED displays. Here, we comprehensively review the latest progress concerning the implementation of mu-LEDs and QDs in display technology, including mu-LED design and fabrication, large-scale mu-LED transfer and QD full-colour strategy. Outlooks on QD stability, patterning and deposition and challenges of mu-LED displays are also provided. Finally, we discuss the advanced applications of QD-based mu-LED displays, showing the bright future of this technology. Micro-LEDs: A fine display by quantum dots Micrometre-sized light-emitting diodes (LEDs) based on quantum dots (QDs) will propel the next generation of display technologies, a review by leading researchers shows. Conventional LED designs, with phosphor coatings that convert light to different colours, are difficult to make smaller than 20 micrometres. Jr-Hau He at City University of Hong Kong and co-workers explain how this problem can be tackled using QDs, tiny particles whose optical properties can be tuned by varying their size, providing brighter and more precise colours. Ultra-high-resolution displays based on phospholuminescent QD-LEDs are now being released to the market thanks to finely-controlled methods for synthesising QDs and depositing them onto films. Further research should focus on the best ways to stabilise and protect QD films within LEDs, and to continue developing electroluminescent QD-LEDs, which could potentially outperform their phospholuminescent cousins.
Monolithic 3D CMOS Using Layered Semiconductors
(2016-04-06)
Sachid, Angada B.
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Tosun, Mahmut
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Desai, Sujay B.
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Hsu, Ching-Yi
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Lien, Der-Hsien
Monolithic 3D integrated circuits using transition metal dichalcogenide materials and low-temperature processing are reported. A variety of digital and analog circuits are implemented on two sequentially integrated layers of devices. Inverter circuit operation at an ultralow supply voltage of 150 mV is achieved, paving the way to high-density, ultralow-voltage, and ultralow-power applications.