Browsing by Author "Yang, Zu-Po"

Now showing 1 - 20 of 46

A curvature-tunable random laser
(2019-02-28)
Lee, Ya-Ju
;
Yeh, Ting-Wei
;
Yang, Zu-Po
;
Yao, Yung-Chi
;
Chang, Chen-Yu
The application of random lasers has been restricted due to the absence of a well-defined resonant cavity, as the lasing action mainly depends on multiple light scattering induced by intrinsic disorders of the laser medium to establish the required optical feedback that hence increases the difficulty in efficiently tuning and modulating random lasing emissions. This study investigated whether the transport mean free path of emitted photons within disordered scatterers composed of ZnO nanowires is tunable by a curvature bending applied to the flexible polyethylene terephthalate (PET) substrate underneath, thereby creating a unique light source that can be operated above and below the lasing threshold for desirable spectral emissions. For the first time, the developed curvature-tunable random laser is implemented for in vivo biological imaging with much lower speckle noise compared to the non-lasing situation through simple mechanical bending, which is of great potential for studying the fast-moving physiological phenomenon such as blood flow patterns in mouse ear skin. It is expected that the experimental demonstration of the curvature-tunable random laser can provide a new route to develop disorder-based optoelectronic devices.
A demonstration of solid-state white light-emitting electrochemical cells using the integrated on-chip plasmonic notch filters
(2016)
Lee, Ya-Ju
;
Lin, Chia-Ching
;
Lee, Hsiao-Chin
;
Yao, Yung-Chi
;
Sarma, Monima
In this study, we demonstrate solid-state white light-emitting electrochemical cells (LECs) using an integrated plasmonic notch filter to tailor the electroluminescence (EL) spectrum of non-doped blue-green emissive material. The plasmonic notch filter is composed of randomly distributed silver nanoparticles (Ag-NPs) embedded in the anode contact of indium tin oxide (ITO). This plasmonic notch filter strongly absorbs green light due to local surface plasmon (LSP) resonance of the Ag-NPs embedded in ITO. Thus, the emission green light of the solid-state LEC is strongly suppressed, leaving the blue and red light output to generate a white EL emission. Moreover, the duration of white EL can be maintained for a longer time under operation, which overcomes the issues regarding the short lifetime of white EL generated by the microcavity effect. In addition, the Ag-NPs can be readily fabricated by the thermal annealing of Ag film, which is compatible with current fabrication technologies typically used in light-emitting diode (LED) industry. Therefore, solid-state white LECs using an integrated on-chip plasmonic notch filter have great potential for applications in solid-state lighting.
Achieving graded refractive index by use of ZnO nanorods/TiO2 layer to enhance omnidirectional photovoltaic performances of InGaP/GaAs/Ge triple-junction solar cells
(2015-05-01)
Tsai, Meng-Tsan
;
Yang, Zu-Po
;
Jing, Ting-Shivan
;
Hsieh, Hsing-Hua
;
Yao, Yung-Chi
In this study, we theoretically and experimentally demonstrate high performance of antireflection (AR) coating composed of the ZnO nanorods (NRs) and TiO2 layers applied on InGaP/GaAs/Ge triple-junction solar cells. The high performance of this AR coating is due to the realization of a smooth gradient profile of refractive index fabricated by only two physical layers. First, due to the inherent inhomogeneous-nanoporous geometry along the surface normal, the ZnO NRs are reasonable to be considered as discrete multiple optical layers with low scattering loss, leading to the index smoothly increasing from air ambient toward down to the solar cells. Second, to compensate the gap of index between ZnO and solar cells, an additional TiO2 layer with index in between is hence necessary to insert under ZnO NRs, significantly further reducing the Fresnel reflection loss of the entire device. The ZnO NRs/TiO2 layer shows a low wavelength-averaged (solar spectrum weighted) reflectance of 6.00% (4.78%) over a wide spectral range of lambda=380-1800 nm, and exhibits a hydrophobic surface with a water contact angle of 128.2 degrees. At device level, we compared the photovoltaic performance of solar cells with and without AR coating, the short-circuit density (J(SC)) is enhanced by 31.8% and 23.8% for solar cells integrated with the ZnO NR5/TiO2 layer and conventional SiO2/TiO2 double-layer AR (DLAR) coating, respectively. Under a very large incident angle of solar illumination (theta=80 degrees), the ZnO NRs/TiO2 layer remains static with J(SC) enhancement of 35.2%, whereas the J(SC) enhancement of conventional DLAR coating drops down to 9.4%. In addition, the ZnO NRs/TiO2 layer barely affects the open-circuit voltage and fill factor of the solar device. Therefore, the proposed ZnO NR5/TiO2 layer with a smoother graded refractive index change is highly promising for the AR coating applications for the next-generation solar cells. (C) 2014 Elsevier B.V. All rights reserved.
Achieving highly saturated single-color and high color-rendering-index white light-emitting electrochemical cells by CsPbX3 perovskite color conversion layers
(2018-12-21)
Wang, Cheng-Ming
;
Su, Yong-Ming
;
Shih, Ting-An
;
Chen, Guan-Yu
;
Chen, Yan-Zhi
Solid-state light-emitting electrochemical cells (LECs) have been thought to be applicable for display and lighting due to their advantages such as simple device architecture, low-voltage operation and compatibility with inert cathode metals. Among the emissive materials of LECs, ionic transition metal complexes (iTMCs) exhibit relatively higher emission efficiency but they show relatively broader emission spectra, resulting in lower color saturation for display application. Here, we demonstrated that by integrating perovskite-based color conversion layers (CCLs) with blue iTMC-LECs, highly saturated green, yellow, red and deep-red and high color-rendering-index (CRI) white LECs can be obtained. The Commission Internationale de l'E'clairage (CIE) 1931 coordinates of the highly saturated single-color LECs are almost on the boundary of the National Television System Committee (NTSC) color gamut, showing their potential application in display. By mixing perovskites of different colors at an appropriate ratio in the CCLs, the white LECs show a CRI >90, which is among the highest reported values, and a correlated color temperature of 2649 K. Hence the proposed technique can also be one of the good candidates for lighting applications. In addition, both the highly saturated single-color and white LECs still exhibit efficient emission for display and lighting applications.
Adjusting Color Temperature of Electroluminescence from White Light-Emitting Electrochemical Cells by Laser-Scanned Annealing of Nanoparticles
(2017-01-01)
Lee, Hsiao-Chin
;
Chiang, Chien-Ming Fan
;
Wu, Po-Yi
;
Yao, Yung-Chi
;
Sarma, Monima
Color temperature of electroluminescence from white light-emitting electrochemical cells can be adjusted by locally laser-scanned thermal annealing on a semi-continuous thin Ag film embedded between indium tin oxide anode and glass substrate. The proposed technique offers programmable versatility to control white electroluminescence and is compatible with display manufacturing technologies.
Atomic Layer Deposition TiO2 Films and TiO2/SiNx Stacks Applied for Silicon Solar Cells
(2016-08-01)
Yang, Zu-Po
;
Cheng, Hsyi-En
;
Chang, I-Hsuan
;
Yu, Ing-Song
;
光電系統研究所
Titanium oxide (TiO2) films and TiO2/SiNx stacks have potential in surface passivation, anti-reflection coatings and carrier-selective contact layers for crystalline Si solar cells. A Si wafer, deposited with 8-nm-thick TiO2 film by atomic layer deposition, has a surface recombination velocity as low as 14.93 cm/s at the injection level of 1.0 x 1015 cm(-3). However, the performance of silicon surface passivation of the deposited TiO2 film declines as its thickness increases, probably because of the stress effects, phase transformation, atomic hydrogen and thermal stability of amorphous TiO2 films. For the characterization of 66-nm-thick TiO2 film, the results of transmission electron microscopy show that the anatase TiO2 crystallinity forms close to the surface of the Si. Secondary ion mass spectrometry shows the atomic hydrogen at the interface of TiO2 and Si which serves for chemical passivation. The crystal size of anatase TiO2 and the homogeneity of TiO2 film can be deduced by the measurements of Raman spectroscopy and spectroscopic ellipsometry, respectively. For the passivating contacts of solar cells, in addition, a stack composed of 8-nm-thick TiO2 film and a plasma-enhanced chemical-vapor-deposited 72-nm-thick SiNx layer has been investigated. From the results of the measurement of the reflectivity and effective carrier lifetime, TiO2/SiNx stacks on Si wafers perform with low reflectivity and some degree of surface passivation for the Si wafer.
Bending-induced tunable threshold in random laser
(2019-01-01)
Lee, Ya-Ju
;
Yeh, Ting-Wei
;
Yang, Zu-Po
;
Yao, Yung-Chi
;
Chang, Chen-Yu
We investigate the case that the transport mean free path of emitted photons within the disordered scatterers, which is composed by the ZnO nanowires, is tunable by a curvature bending applied on the flexible polyethylene terephthalate substrate underneath, thereby creating a unique light source which is able to be operated above and below the lasing threshold for desirable spectral emissions. (C) 2019 The Author(s)
Cationic Ir-III Emitters with Near-Infrared Emission Beyond 800 nm and Their Use in Light-Emitting Electrochemical Cells
(2019-04-11)
Chen, Guan-Yu
;
Chang, Bo-Ren
;
Shih, Ting-An
;
Lin, Chien-Hsiang
;
Lo, Chieh-Liang
Solid-state near-infrared (NIR) light-emitting devices have recently received considerable attention as MR light sources that can penetrate deep into human tissue and are suitable for bioimaging and labeling. in addition, solidstate NIR light-emitting electrochemical cells (LECs) have shown several promising advantages over NIR organic light-emitting devices (OLEDs). However, among the reported NIR LECs based on ionic transition-metal complexes (iTMCs), there is currently no iridium-based LEC that displays NIR electroluminescence (EL) peaks near to or above 800 nm. In this report we demonstrate a simple method for adjusting the energy gap between the highest-occupied molecular orbital (HOMO) and the lowest-unoccupied molecular orbital (LUMO) of iridium-based iTMCs to generate NIR emission. We describe a series of novel ionic iridium complexes with very small energy gaps, namely NIR1-NIR6, in which 2,3-diphenylbenzo[g]quinoxaline moieties mainly take charge of the HOMO energy levels and 2,2'-biquinoline, 2-(quinolin-2-yl)quinazoline, and 2,2'-bibenzo[d]thiazole moieties mainly control the LUMO energy levels. All the complexes exhibited NIR phosphorescence, with emission maxima up to 850 nm, and have been applied as components in LECs, showing a maximum external quantum efficiency (EQE) of 0.05% in the EL devices. By using a host-guest emissive system, with the iridium complex RED as the host and the complex NIR3 or NIR6 as guest, the highest EQE of the LECs can be further enhanced to above 0.1%.
Coherent and Polarized Random Laser Emissions from Colloidal CdSe/ZnS Quantum Dots Plasmonically Coupled to Ellipsoidal Ag Nanoparticles
(2017-02)
Yao, Yung-Chi
;
Yang, Zu-Po
;
Hwang, Jung-Min
;
Su, Hai-Ching
;
Haung, Jing-Yu
This study demonstrates the capability of controlling optical anisotropy of lasing emissions by manipulating the coupling strength spatially and spectrally between the oscillated electric field of emitted light and the localized surface plasmon (LSP) resonance for a random lasing medium composed of colloidal CdSe/ZnS quantum dots (QDs) and ellipsoidal silver nanoparticles (Ag NPs). Distinctive from the amplified spontaneous emission generally observed on colloidal CdSe/ZnS QDs, it has been found that lasing emissions of the revealed system exhibit clear interference features (coherent optical feedbacks) with low-threshold characteristics, mainly attributed to enhanced light scatterings and optical gains arisen in peripheral surfaces of ellipsoidal Ag NPs. Importantly, the relative orientation, between the oscillated electric field of emitted light from colloidal CdSe/ZnS QDs and the ellipse axis of Ag NPs, plays a critical role in selective excitation of LSP resonances leading to laser emissions with preferential optical polarizations. The achievement of spatial and spectral coupling of LSP resonance with colloidal QDs, respectively, by spin coating thin QDs film on Ag NPs and control of the Ag NP geometry makes the present system one of the promising candidates of colloidal QDs-based random lasers to achieve coherent and polarized lasing emissions.
Develop a Low-Temperature In-Line Sputtering System for Flexible and Thinned-Glass Substrates
(2016-11)
Wang, Yao-Chin
;
Lin, Bor-Shyh
;
Yang, Zu-Po
;
光電學院
;
光電系統研究所
Flexible and thinned glass substrates are two kinds of important substrates but are difficult to handle by conventional in-line sputtering system for mass production. Here, we designed and developed an in-line sputtering system for mass production that can handle these two kinds of substrates. The key of this success is the well heat management of this system. With the method of multiple cycles of deposition and cooling, this system demonstrated the deposition of thick copper film on flexible substrates at substrate temperature less than 120 degrees C. The thickness and cooling rate for one cycle are similar to 800 nm and 0.5 degrees C/s, respectively. Additionally, the processes of deposition and cooling are parallel in our system. By redesigning the mechanical structure of substrate carrier, the effect of the thermal stress change of substrate carrier on thinned glass substrates is minimized; therefore, our system can uniformly deposited ITO film on large-size thinned glass substrates. The values of sheet resistance, transmittance, and their uniformity are acceptable for industry. Moreover, all the processes of this system are automatic which is ready for mass production.
Dual wavelength silicon-based-photodetector for biomedical sensing system applications
(2016)
Wang, Yao-Chin
;
Yang, Zu-Po
;
Lin, Bor-Shyh
;
光電系統研究所
;
影像與生醫光電研究所
the article proposed dual wavelength silicon based photo detector with multi-layer structure, was fabricated and characterized with dual wavelength enhanced operating. We proposed the dual wavelength response of the silicon based bio-photo-detector. It can be enhanced by introducing thin porous silicon layer as the base region of transistor. The device process of manufacture is suitable in design of visible-light sensitive bio-photo-detectors. The experimental results showed that the dual wavelength responses in the developed devices were enhanced as compared to the silicon-based homo-junction photo-detectors in optical parameters, which indicated that the developed bio-photo-detector showed potential for practical silicon based biomedical device and system applications.
Dynamically tuning the correlated color temperature of white light-emitting electrochemical cells with electrochromic filters
(2017-09-01)
Chiou, Bo-Ruei
;
Lee, Hsiao-Chin
;
Jang, Yea-Fen
;
Yang, Zu-Po
;
Wang, Yao-Chin
Recently, white solid-state light-emitting electrochemical cells (LECs) have drawn great attention since they exhibit advantages such as low-voltage operation, compatibility with solution processes and employing inert cathode metals. Since different correlated color temperatures (CCTs) of background illumination are necessary for various lighting applications, a real-time tunable CCT of white LECs would be highly desired in modern smart lighting systems. In this work, a widely and dynamically tuning CCT (>10000 K) of white LEC is demonstrated by employing an electrochromic device (ECD) as a real-time controllable color filter. By increasing the applied bias on the ECD to attenuate more the red parts of white EL from the white LEC, the LEC-based white light source becomes more bluish and, in consequence, shows higher CCT. This proposed LEC-based white light source with the characteristics of wide CCT range and real-time tunability is suitable for most lighting applications and modern smart lighting systems. (C) 2017 Elsevier B.V. All rights reserved.
Effects of N/Ga flux ratio on GaN films grown on 4H-SiC substrate with 4 degrees miscutting orientation by plasma-assisted molecular beam epitaxy
(2017-07-05)
Susanto, Iwan
;
Tsou, Tsung-Han
;
Yang, Zu-Po
;
Lee, Chao-Yu
;
Li, Hui
High-quality GaN films grown on 4H-SiC (0001) substrate with 4 of miscutting orientation have been done by plasma-assisted molecular beam epitaxy with different N/Ga flux ratio. The effect of N/Ga flux ratio on the surface morphology, chemical composition, structural and optical properties was systematically investigated. The observations of in-situ reflective high-energy electron diffraction demonstrated the special surface of SiC substrate and GaN growth transition from two-to three-dimension depending on N/Ga flux ratio. In the Ga-rich condition for epitaxy, Ga droplets formed and the root mean square value of surface roughness increased by the characterizations of scanning electron microscopy and atomic force microscopy which also related to the formation of the pits on the surface due to the accumulation of excess Ga on the surface. The better growth parameter of GaN films in the work is N/Ga flux ratio of 28 at substrate temperature 700 degrees C. Its surface oxide and charge-compensated surface state associated with defects are minimized from the surface composition analysis of X-ray photoelectron spectroscopy. In the structural characterization of high-resolution X-ray diffraction, the value of full width at half maximum and density of threading dislocation are lower to prove the high-quality structure of GaN film grown at N/Ga flux ratio of 28. Finally, the photoluminescence analysis performed the narrow near-band-edge peak and yellow band, corresponding to the better quality of GaN films. In this report, high-quality GaN films on 4H-SiC (0001) with 4 of miscutting orientation have been demonstrated by the reduction of defect states via the different N/Ga flux ratio. N/Ga flux ratio not only influences the growth mechanism and surface morphology, but also the surface chemical composition, crystal quality and optical properties of GaN compound semiconductors. (C) 2017 Elsevier B.V. All rights reserved.
Effects of substrate and annealing on GaN films grown by plasma-assisted molecular beam epitaxy
(2017-06-25)
Yang, Zu-Po
;
Tsou, Tsung-Han
;
Lee, Chao-Yu
;
Kan, Ken-Yuan
;
Yu, Ing-Song
GaN films were deposited by plasma-assisted molecular beam epitaxy on different substrates, i.e. Si (111), Sapphire (0001) and 4H-SiC (0001) with 4 degrees of miscutting orientation. Due to the lattice mismatch between GaN films and substrates, the substrates profoundly affect the growth mechanism of GaN films on them during the epitaxy. The smooth and complete GaN films can be obtained on 4H-SiC substrates based on the analyses of reflection high energy electron diffraction, scanning electron microscopy and atomic force microscopy. Higher quality of GaN films on 4H-SiC was also confirmed by high resolution X-ray diffraction. Photoluminescence measurements show that the compress stress existed in GaN films grown on sapphire, but tensile stress was observed in the films grown on 4H-SiC and Si. Meanwhile, in-situ annealing treatment of post expitxy can remove Ga droplets on GaN films and decrease the surface roughness and defect density of GaN films; however, thermal decomposition on the surface of GaN films was observed in the characterizations of X-ray photoelectron spectroscopy. (C) 2016 Elsevier B.V. All rights reserved.
Enhanced external quantum efficiency in GaN-based vertical-type light-emitting diodes by localized surface plasmons
(2016-03-03)
Yao, Yung-Chi
;
Hwang, Jung-Min
;
Yang, Zu-Po
;
Haung, Jing-Yu
;
Lin, Chia-Ching
Enhancement of the external quantum efficiency of a GaN-based vertical-type light emitting diode (VLED) through the coupling of localized surface plasmon (LSP) resonance with the wave-guided mode light is studied. To achieve this experimentally, Ag nanoparticles (NPs), as the LSP resonant source, are drop-casted on the most top layer of waveguide channel, which is composed of hydrothermally synthesized ZnO nanorods capped on the top of GaN-based VLED. Enhanced light-output power and external quantum efficiency are observed, and the amount of enhancement remains steady with the increase of the injected currents. To understand the observations theoretically, the absorption spectra and the electric field distributions of the VLED with and without Ag NPs decorated on ZnO NRs are determined using the finite-difference time-domain (FDTD) method. The results prove that the observation of enhancement of the external quantum efficiency can be attributed to the creation of an extra escape channel for trapped light due to the coupling of the LSP with wave-guided mode light, by which the energy of wave-guided mode light can be transferred to the efficient light scattering center of the LSP.
Enhancement for Potential-Induced Degradation Resistance of Crystalline Silicon Solar Cells via Anti-Reflection Coating by Industrial PECVD Methods
(2018-12-01)
Chen, Tsung-Cheng
;
Kuo, Ting-Wei
;
Lin, Yu-Ling
;
Ku, Chen-Hao
;
Yang, Zu-Po
The issue of potential-induced degradation (PID) has gained more concerns due to causing the catastrophic failures in photovoltaic (PV) modules. One of the approaches to diminish PID is to modify the anti-reflection coating (ARC) layer upon the front surface of crystalline silicon solar cells. Here, we focus on the modification of ARC films to realize PID-free step-by-step through three delicate experiments. Firstly, the ARC films deposited by direct plasma enhanced chemical vapor deposition (PECVD) and by indirect PECVD were investigated. The results showed that the efficiency degradation of solar cells by indirect PECVD method is up to -33.82%, which is out of the IEC 62804 standard and is significantly more severe than by the direct PECVD method (-0.82%). Next, the performance of PID-resist for the solar cell via indirect PECVD was improved significantly (PID reduced from -31.82% to -2.79%) by a pre-oxidation step, which not only meets the standard but also has higher throughput than direct PECVD. Lastly, we applied a novel PECVD technology, called the pulsed-plasma (PP) PECVD method, to deal with the PID issue. The results of the HF-etching rate test and FTIR measurement indicated the films deposited by PP PECVD have higher potential against PID in consideration of less oxygen content in this film. That demonstrated the film properties were changed by applied a new control of freedom, i.e., PP method. In addition, the 96 h PID result of the integrated PP method was only -2.07%, which was comparable to that of the integrated traditional CF method. In summary, we proposed three effective or potential approaches to eliminate the PID issue, and all approaches satisfied the IEC 62804 standard of less than 5% power loss in PV modules.
Enhancement of hydrogen evolution reaction by Pt nanopillar-array electrode in alkaline media and the effect of nanopillar length on the electrode efficiency
(2019-11-15)
Cheng, Hsyi-En
;
Li, Wen-Lung
;
Yang, Zu-Po
;
光電系統研究所
;
Institute of Photonic System
Pt nanopillar-array 3D electrodes with nanopillar length of 150, 450 and 900 nm and nanopillar density of similar to 10(9) cm(-2) were fabricated. Their catalytic activity for hydrogen evolution reaction (HER) was evaluated by linear sweep voltammetry and electrochemical impedance spectroscopy. In comparison with straightly electrodeposited black Pt film and forged Pt sheet electrodes, the HER current density has been significantly improved by the nanopillar-array architecture. The overpotential of HER at current density of 10 mA cm(-2) at 26 degrees C is as low as 78 mV, lower than the black Pt film of 107 mV and the Pt sheet of 174 mV. The improvement of HER is ascribed to the low charge transfer resistance of the 3D electrode and the high desorption capability of hydrogen bubbles at the nanotips. Interestingly, the nanopillar-array 3D electrode has an optimal nanopillar length for HER. The mechanisms for the optimal nanopillar length were investigated here. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Enhancing extracted electroluminescence from light-emitting electrochemical cells by employing high-refractive-index substrates
(2017-12-01)
Jang, Yea-Fen
;
Lin, Tzu-Chun
;
Guo, Jhih-Yan
;
Chiang, Chien-Ming Fan
;
Wu, Ming-Lun
Solidstate lightemitting electrochemical cells (LECs) show several advantages over conventional organic lightemitting devices (OLEDs) such as simple device structure compatible with solution processes, low operation voltage and capability of utilizing inert cathode metals. However, device performance of LECs must be improved, e.g. enhancing light extraction, to meet the requirements for practical applications. Among the optical modes trapped in LECs, light trapped in substrate mode is easier to be extracted, e.g., by simply roughing the output surface. Therefore, increasing the percentage of substrate mode is beneficial in improving light extraction. In this work, the contributions of optical modes in LECs employing substrates with various refractive indices are analyzed. Higherrefractiveindex substrates are shown to trap more light in the substrates. Smaller refractive index difference between higher-refractive-index substrate and indium tin oxide (ITO) layer also increases the cutoff spectral range of light waveguided in ITO layer. Furthermore, light intensity in surface plasmon mode significantly reduces as the refractive index of the substrate increases. Reducing the percentage of surface plasmon mode facilitates light extraction since it requires more complicated methods for outcoupling light in this mode. With commercially available unpolished sapphire substrates, light output of LECs is enhanced by 56%. When a scattering layer was inserted between ITO and sapphire substrate, more light in substrate mode can be extracted and 71% enhancement in light output is realized. High external quantum efficiency up to 5.5% is consequently obtained in LECs based on a ruthenium complex. Such device efficiency is among the highest reported values for redemitting LECs and thus confirms that utilizing higher-refractive-index substrates would offer a simple and feasible approach to improve light output of LECs. In comparison to OLEDs, increased EL trapped in substrates of LECs mainly comes from surface plasmon mode rather than waveguide mode. (C) 2017 Elsevier B.V. All rights reserved.
Enhancing UV-emissions through optical and electronic dual-function tuning of Ag nanoparticles hybridized with n-ZnO nanorods/p-GaN heterojunction light-emitting diodes
(2016)
Yao, Yung-Chi
;
Yang, Zu-Po
;
Hwang, Jung-Min
;
Chuang, Yi-Lun
;
Lin, Chia-Ching
ZnO nanorods (NRs) and Ag nanoparticles (NPs) are known to enhance the luminescence of light-emitting diodes (LEDs) through the high directionality of waveguide mode transmission and efficient energy transfer of localized surface plasmon (LSP) resonances, respectively. In this work, we have demonstrated Ag NP-incorporated n-ZnO NRs/p-GaN heterojunctions by facilely hydrothermally growing ZnO NRs on Ag NP-covered GaN, in which the Ag NPs were introduced and randomly distributed on the p-GaN surface to excite the LSP resonances. Compared with the reference LED, the light-output power of the near-band-edge (NBE) emission (ZnO, lambda = 380 nm) of our hybridized structure is increased almost 1.5-2 times and can be further modified in a controlled manner by varying the surface morphology of the surrounding medium of the Ag NPs. The improved light-output power is mainly attributed to the LSP resonance between the NBE emission of ZnO NRs and LSPs in Ag NPs. We also observed different behaviors in the electroluminescence (EL) spectra as the injection current increases for the treatment and reference LEDs. This observation might be attributed to the modification of the energy band diagram for introducing Ag NPs at the interface between n-ZnO NRs and p-GaN. Our results pave the way for developing advanced nano-structured LED devices with high luminescence efficiency in the UV emission regime.
Flexible random lasers with tunable lasing emissions
(2018-06-14)
Lee, Ya-Ju
;
Chou, Chun-Yang
;
Yang, Zu-Po
;
Thi Bich Hanh Nguyen
;
Yao, Yung-Chi
In this study, we experimentally demonstrated a flexible random laser fabricated on a polyethylene terephthalate (PET) substrate with a high degree of tunability in lasing emissions. Random lasing oscillation arises mainly from the resonance coupling between the emitted photons of gain medium (Rhodamine 6G, R6G) and the localized surface plasmon (LSP) of silver nanoprisms (Ag NPRs), which increases the effective cross-section for multiple light scattering, thus stimulating the lasing emissions. More importantly, it was found that the random lasing wavelength is blue-shifted monolithically with the increase in bending strains exerted on the PET substrate, and a maximum shift of similar to 15 nm was achieved in the lasing wavelength, when a 50% bending strain was exerted on the PET substrate. Such observation is highly repeatable and reversible, and this validates that we can control the lasing wavelength by simply bending the flexible substrate decorated with the Ag NPRs. The scattering spectrum of the Ag NPRs was obtained using a dark-field microscope to understand the mechanism for the dependence of the wavelength shift on the exerted bending strains. As a result, we believe that the experimental demonstration of tunable lasing emissions based on the revealed structure is expected to open up a new application field of random lasers.