Browsing by Author "Li, Yu-Ren"

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Annealing effect on the photoluminescence characteristics of ZnO-nanowires and the improved optoelectronic characteristics of p-NiO/n-ZnO nanowire UV detectors
(2015-06-01)
Li, Yu-Ren
;
Wan, Chung-Yun
;
Chang, Chia-Tsung
;
Huang, Yu-Chin
;
Tsai, Wan-Lin
Transparent ultraviolet (UV) detectors with nanoheterojunctions (NHJs) of p-type NiO and n-type ZnO nanowires (ZnO-NWs) were successfully fabricated using a DC sputtering system and a hydrothermal process, respectively. After annealing in nitrogen ambient, the near-band-edge emission to deep level emission ratio (NBE/DLE) of ZnO-NWs gradually increased as the temperature increased and reached a maximum of 28.9 at a temperature setting of 500 degrees C. In contrast, after annealing in oxygen atmosphere, the NBE/DLE of ZnO-NWs initially increased from 1.2 to 5.9 and then decreased to 3.2. At a reverse bias of 2V, the devices with the 500-degrees C-N-2-annealed ZnO-NWs exhibited better sensitivity (J(UV)/J(Dark) = 5.65; J(Visible)/J(Dark) = 1.35) to UV light (365 nm, 0.3 mW/cm(2)) than those with the as-grown ZnO-NWs (J(UV)/J(Dark) = 4.98; J(Visible)/J(Dark) = 3.82) because the structural defects in ZnO-NWs were effectively eliminated after annealing in nitrogen ambient at 500 degrees C. (C) 2015 The Japan Society of Applied Physics
Approaching conversion limit with all-dielectric solar cell reflectors
(2015-02-09)
Fu, Sze Ming
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Lai, Yi-Chun
;
Tseng, Chi Wei
;
Yan, Sheng Lun
;
Zhong, Yan Kai
Metallic back reflectors has been used for thin-film and wafer-based solar cells for very long time. Nonetheless, the metallic mirrors might not be the best choices for photovoltaics. In this work, we show that solar cells with all-dielectric reflectors can surpass the best-configured metal-backed devices. Theoretical and experimental results all show that superior large-angle light scattering capability can be achieved by the diffuse medium reflectors, and the solar cell J-V enhancement is higher for solar cells using all-dielectric reflectors. Specifically, the measured diffused scattering efficiency (D.S.E.) of a diffuse medium reflector is >0.8 for the light trapping spectral range (600nm-1000nm), and the measured reflectance of a diffuse medium can be as high as silver if the geometry of embedded titanium oxide(TiO2) nanoparticles is optimized. Moreover, the diffuse medium reflectors have the additional advantage of room-temperature processing, low cost, and very high throughput. We believe that using all-dielectric solar cell reflectors is a way to approach the thermodynamic conversion limit by completely excluding metallic dissipation. (C) 2015 Optical Society of America
Conductivity enhancement of multiwalled carbon nanotube thin film via thermal compression method
(2014-08-29)
Tsai, Wan-Lin
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Wang, Kuang-Yu
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Chang, Yao-Jen
;
Li, Yu-Ren
;
Yang, Po-Yu
For the first time, the thermal compression method is applied to effectively enhance the electrical conductivity of carbon nanotube thin films (CNTFs). With the assistance of heat and pressure on the CNTFs, the neighbor multiwalled carbon nanotubes (CNTs) start to link with each other, and then these separated CNTs are twined into a continuous film while the compression force, duration, and temperature are quite enough for the reaction. Under the compression temperature of 400 degrees C and the compression force of 100 N for 50 min, the sheet resistance can be reduced from 17 to 0.9 k Omega/sq for the CNTFs with a thickness of 230 nm. Moreover, the effects of compression temperature and the duration of thermal compression on the conductivity of CNTF are also discussed in this work.
Densification effects of the carbon nanotube pillar array on field-emission properties
(2016-06)
Wang, Kuang-Yu
;
Chou, Chia-Hsin
;
Liao, Chan-Yu
;
Li, Yu-Ren
;
Cheng, Huang-Chung
In this study, a simple densification method for carbon nanotube (CNT) pillars is proposed to achieve high-performance field emission characteristics and stable emission. Through capillary force during solution evaporation, the CNT density in each pillar can be increased by about six times without causing damage to the crystallinity of CNTs. The densified CNT pillars exhibit lower series resistance, sharper pillars, better contacts, higher thermal conductivity, and better mechanical stiffness than as-grown ones. Therefore, the threshold field of the field emitter with such CNT pillars of 50 mu m height can be reduced to 1.98 V/mu m, as compared with 2.2V/mu m for the undensified ones. Moreover, the fluctuation of field-emission current decreases from 15.5 to 9.4% after the stress tests at a field of 2V/mu m for 1800 s. These findings imply that the densified CNT pillars are promising for the field-emission applications. (C) 2016 The Japan Society of Applied Physics
Densification effects of the carbon nanotube pillar array on field-emission properties
(2016-06-01)
Wang, Kuang-Yu
;
Chou, Chia-Hsin
;
Liao, Chan-Yu
;
Li, Yu-Ren
;
Cheng, Huang-Chung
In this study, a simple densification method for carbon nanotube (CNT) pillars is proposed to achieve high-performance field emission characteristics and stable emission. Through capillary force during solution evaporation, the CNT density in each pillar can be increased by about six times without causing damage to the crystallinity of CNTs. The densified CNT pillars exhibit lower series resistance, sharper pillars, better contacts, higher thermal conductivity, and better mechanical stiffness than as-grown ones. Therefore, the threshold field of the field emitter with such CNT pillars of 50 mu m height can be reduced to 1.98 V/mu m, as compared with 2.2V/mu m for the undensified ones. Moreover, the fluctuation of field-emission current decreases from 15.5 to 9.4% after the stress tests at a field of 2V/mu m for 1800 s. These findings imply that the densified CNT pillars are promising for the field-emission applications. (C) 2016 The Japan Society of Applied Physics
Effect of arrangement of carbon nanotube pillars on its gas ionization characteristics
(2013-06-01)
Chang, Chia-Tsung
;
Huang, Chun-Yu
;
Li, Yu-Ren
;
Cheng, Huang-Chung
;
電子工程學系及電子研究所
The gas ionization sensors (GISs) using the carbon nanotube (CNT) pillars which has the pillar height (H) of 15 mu m with interpillar spacing (R) of 30 mu m as the cathode had been proposed for the first time to exhibit the 20 times higher field enhancement factor (beta) and the lower breakdown voltage of 350V with respect to the CNT film ones for nitrogen gas at the pressure of 0.035 Torr. As the H increased from 5 mu m to 15 mu m, the beta increased with increasing the H since the electrical field could be enhanced via the aspect ratio increment. However, as the H increased from 15 mu m to 60 mu m, the beta decreased with increasing the H owing to the increased field-screening effect. Such an optimum GIS with the CNT pillars also exhibited high sensitivity and selectivity for different kinds of gases detection as well as the good linearity for detecting the gas mixture. (C) 2013 Elsevier B.V. All rights reserved.
Effect of oxygen plasma treatment on horizontally aligned carbon nanotube thin film as pH-sensing membrane of extended-gate field-effect transistor
(2015-04-01)
Wang, Kuang-Yu
;
Tsai, Wan-Lin
;
Yang, Po-Yu
;
Chou, Chia-Hsin
;
Li, Yu-Ren
The high-performance pH-sensing membrane of extended-gate field-effect transistors (EGFET) composed of high-conductivity horizontally aligned carbon nanotube thin films (HACNTFs) after oxygen plasma treatment is successfully demonstrated. The 10-mu m-wide catalytic metal lines with 60 mu m interspace produced CNT vertical plates, and the plates were mechanically pulled down and densified to form HACNTFs. A large amount of oxygen-containing functional groups are decorated on the CNTs after the oxygen plasma treatment. These functional groups act as the sensing sites and respond to the H+ or OH- ions in solutions with different pH values. Therefore, these functionalized HACNTFs as pH-EGFET-sensing membranes can achieve a high voltage sensitivity of 40 mV/pH and high current sensitivity of 0.78 mu A(1/2)/pH. Moreover, large linearity of 0.998 is measured in a wide sensing range from pH 1 to 13. These results reveal that the oxygen plasma treatment is an effective way to improve the CNT-sensing characteristics in pH-EGFET sensors. (C) 2015 The Japan Society of Applied Physics
Effect of substrate preheating on the photovoltaic performance of ZnO nanorod-based perovskite solar cells
(2018-06-01)
Li, Wei-Shuo
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Lin, Tsyr-Rou
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Yang, Hsiu-Ting
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Li, Yu-Ren
;
Chuang, Kai-Chi
In this study, zinc oxide nanorods (ZnO-NRs) grown via a low-temperature hydrothermal growth process are used as the electron transport layer (ETL) owing to their low temperature process and three-dimensional structure, which increases the surface area and thereby improves photovoltaic performance. To further improve the performance of solar cells, substrate preheating before spin-coating PbI2 and perovskite films was conducted. With the increase in preheating temperature, the grain size, surface uniformity, and crystallinity of perovskite increased. Consequently, the photovoltaic performances of the devices with 150-nm-long ZnO-NRs and substrate preheating at 150 degrees C showed an optimum open-circuit voltage (V-oc) of 0.84V, a short-circuit current (J(sc)) of 21.43 mA/cm(2), a fill factor (FF) of 57.42%, and a power conversion efficiency (PCE) of 10.34% owing to the superior quality of the perovskite films having smooth surfaces with fewer pinholes. (c) 2018 The Japan Society of Applied Physics
Experimental and Theoretical Study of Low-Cost Hydrothermally Grown Nanowire Silicon Solar Cell
(2013)
Li, Hung-Hsien
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Lin, Albert S.
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Zhong, Yan-Kai
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Fu, Sze-Ming
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Lai, Shih-Yun
The low cost and high absorbance is the two most important considerations for thin-film silicon photovoltaics. In this work, aluminum doped zinc oxide(AZO) nanowire is grown by low cost hydrothermal method and nano-structured amorphous silicon(alpha-Si) solar cell is realized on these AZO nanowire substrate. The experimental result shows superior light trapping property compared to conventional planar structure with 18.83% improvement in photocurrent. Simulation result shows the required thickness for full absorption for high aspect ratio AZO nanowire solar cell is similar to 0.3 square m, much thinner than planar type solar cell. The calculation reveals that solar cell absorbance increases with the nanowire length and packing density, indicating material volume is the first order effect for nanowire solar cells. The proposed low-cost AZO nanowire array amorphous silicon solar cell is very promising for future nanostructured silicon photovoltaics.
Field Emission Properties of Carbon Nanotube Arrays on the Thickness-Controlled Flexible Substrate by the Pattern Transfer Process
(2012-07-01)
Chang, Chia-Tsung
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Juan, Chuan-Ping
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Lin, Yi-Chan
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Li, Yu-Ren
;
Tsai, Wan-Lin
A technigal with the polydimethylsiloxane (PDMS) solution infiltrated into the SiOx-coated CNTAs has been utilized to directly transfer the CNTAs away from the silicon substrate. The oxide coating layer was utilized to protect the morpholgy of as-grown patterned vertical aligmed carbon nanotube (CNTs) arrays. The high density plasma reactive ions etching (HDP-RIE) system was used to make the CNTs emerge from the surface of the flexible substrate and modify the crystallines of CNTs. After the protecting oxide was HDP-RIE-processed for 8 min, the emission current properties were enhanced to be 1.03 V/mu m and 1.43 V/mu m, respectively, for the turn-on field and the threshold field, as compared with 1.25 V/mu m and 1.59 V/mu m for the as-grown CNTs, accordingly. The Field Emission (FE) enhancement after dry etching could be attributed to the open-ended structures and better crystalline.
Flexible Atmospheric-Pressure Gas Ionization Sensors with Horizontally Aligned Carbon Nanotube Electrodes
(2016-12)
Wang, Kuang-Yu
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Tsai, Wan-Lin
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Yang, Po-Yu
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Chou, Chia-Hsin
;
Liao, Chan-Yu
A flexible atmospheric-pressure gas ionization sensor (GIS) with the horizontally aligned carbon nanotube (HACNT) electrodes in the planar structure has been demonstrated for the first time via the proposed rolling-down technique of CNTs. The gap between the electrodes of high-density and uniform HACNTs could be therefore precisely controlled via adjusting the length of the CNTs and the interspacing between the patterned catalysts. High-performance sensing characteristics to various gases Ar, N-2, air, and O-2 at atmospheric pressure with the breakdown voltages as low as 160, 193, 205, and 233, respectively, have been achieved with the electrode gap of 20 mu m. It is attributed to the field enhancement from the small gap and the double-side nanostructures. The superior flexibility of the proposed GIS with different bending tests has also been obtained. It reflects that the HACNTs possess excellent material properties, including great mechanical strength and good electrical conductivity. Such a simple, low-cost, and flexible GIS is promising for its applications in portable and wearable personal monitoring devices.
Formation and characterization of high-performance silicon thin-film transistors with and without location-controlled grain boundary
(2017-10-01)
Liao, Chan-Yu
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Lin, Hsiao-Chun
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Wang, Chao-Lung
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Lee, I-Che
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Chou, Chia-Hsin
This paper reports the demonstration of structural effects on excimer laser crystallization (ELC) for the Si strip with a recessed-channel structure on the silicon nitride under-layer (RCS-ULN). We revealed that a single location-controlled grain boundary (GB) oriented normal to the Si strip in the middle site without any other GB in the recessed region can be attained via ELC for the RCS-ULN structures with a short recessed region between neighboring long thick regions in a narrow Si strip. This can be attributed to the effective production of a significant 2D lateral thermal gradient in the recessed region and neighboring thick regions. Consequently, the RCS-ULN TFTs fabricated at the position one-half of such an optimal recessed region can achieve a superior field-effect mobility of 670 cm(2) V-1 . s(-1) with minor performance variations since the single-crystal-like Si channel has been adopted.
High-sensitivity extended-gate field-effect transistors as pH sensors with oxygen-modified reduced graphene oxide films coated on different reverse-pyramid silicon structures as sensing heads
(2016-04)
Li, Yu-Ren
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Chang, Shih-hsueh
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Chang, Chia-Tsung
;
Tsai, Wan-Lin
;
Chiu, Yu-Kai
A high-performance extended-gate field-effect transistor (EGFET) as pH sensor with its microstructured sensing head composed of an oxygen-modified reduced graphene oxide film (RGOF) on a reverse-pyramid (RP) Si structure was developed to achieve a high sensitivity of 57.5mV/pH with an excellent linearity of 0.9929 in a wide pH sensing range of 1-13. These features were ascribed to the large amount of sensing sites and large sensing area. In contrast, the planar Si substrate with the oxygen-plasma-treated RGOF (OPT-RGOF) at the optimal bias power showed a sensitivity of 52.9mV/pH compared with 45.0mV/pH for that without plasma treatment. It reveals that oxygen plasma can produce oxygen-containing groups as sensing sites, enhancing proton sensing characteristics. However, oxygen plasma treatment at high bias powers would cause damage to the RGOFs, resulting in poor conducting and sensing properties. On the other hand, the use of the RP structures could increase the effective sensing area and further promote the sensing performance. (C) 2016 The Japan Society of Applied Physics
High-sensitivity extended-gate field-effect transistors as pH sensors with oxygen-modified reduced graphene oxide films coated on different reverse-pyramid silicon structures as sensing heads
(2016-04-01)
Li, Yu-Ren
;
Chang, Shih-hsueh
;
Chang, Chia-Tsung
;
Tsai, Wan-Lin
;
Chiu, Yu-Kai
A high-performance extended-gate field-effect transistor (EGFET) as pH sensor with its microstructured sensing head composed of an oxygen-modified reduced graphene oxide film (RGOF) on a reverse-pyramid (RP) Si structure was developed to achieve a high sensitivity of 57.5mV/pH with an excellent linearity of 0.9929 in a wide pH sensing range of 1-13. These features were ascribed to the large amount of sensing sites and large sensing area. In contrast, the planar Si substrate with the oxygen-plasma-treated RGOF (OPT-RGOF) at the optimal bias power showed a sensitivity of 52.9mV/pH compared with 45.0mV/pH for that without plasma treatment. It reveals that oxygen plasma can produce oxygen-containing groups as sensing sites, enhancing proton sensing characteristics. However, oxygen plasma treatment at high bias powers would cause damage to the RGOFs, resulting in poor conducting and sensing properties. On the other hand, the use of the RP structures could increase the effective sensing area and further promote the sensing performance. (C) 2016 The Japan Society of Applied Physics
Highly Sensitive pH Sensors of Extended-Gate Field-Effect Transistor With the OxygenFunctionalized Reduced Graphene Oxide Films on Reverse Pyramid Substrates
(2015-11-01)
Li, Yu-Ren
;
Chang, Shih-Hsueh
;
Tsai, Wan-Lin
;
Chang, Chia-Tsung
;
Wang, Kuang-Yu
The oxygen-plasma-treated reduced graphene oxide films (OPT-RGOFs) as the pH sensing membranes for the extended-gate field-effect transistors were demonstrated to achieve the higher pH sensitivity of 52 mV/pH and better linearity of 0.996 in a wide sensing range of pH 1-13 than those without plasma treatment. It was attributed to the oxygen-containing functional groups on the RGOF induced from the plasma treatment. In addition, the OPT-RGOFs sprayed on the reverse pyramid substrates were also proposed to further enhance the sensing sites, leading to a superior pH sensitivity of 57 mV/pH with an excellent linearity of 0.996.
Improving the stability and reproducibility of the carbon nanotube gas ionization sensor by Co-Ti/Ti co-deposited catalyst layer
(2013-12-01)
Chang, Chia-Tsung
;
Huang, Chun-Yu
;
Li, Yu-Ren
;
Cheng, Huang-Chung
;
電子工程學系及電子研究所
A novel gas ionization sensor (GIS) of the carbon nanotube (CNT) film using the Co-Ti/Ti co-deposited catalyst layer had been proposed for the first time to exhibit higher stability and better reproducibility with respect to the CNT film ones with the single catalyst layer. For the proposed CNT GIS, the variation of the breakdown voltage (V-br) was less than 25% for the ten devices with the same structure measurement since the lengths of the CNT synthesized were uniform and aligned. Besides, the fluctuation of the V-br was about 14% during 1000 operation times in nitrogen at the pressure of 0.035 Torr. It was attributed to the adhesion between CNTs and the substrate could be improved since the co-deposited catalyst layer and Ti adhesion layer would be coalesced so that the Co nanoparticles would be partially immersed into Ti layer after hydrogen pretreatment. Such a CNT GIS with the co-deposited catalyst layer also exhibited high sensitivity and selectivity for different kinds of gases detection as well as the good linearity for detecting the gas mixture. (C) 2013 Elsevier B.V. All rights reserved.
Location-Controlled Single-Crystal-Like Silicon Thin-Film Transistors by Excimer Laser Crystallization on Recessed-Channel Silicon Strip With Under-Layered Nitride
(2016-09)
Liao, Chan-Yu
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Lin, Hsiao-Chun
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Wang, Chao-Lung
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Lee, I-Che
;
Chou, Chia-Hsin
High-performance Si thin-film transistors (TFTs) on the recessed-channel Si strips with the under-layered nitride film have been fabricated using excimer laser crystallization (ELC). A nitride film was added as a light absorption layer to suppress solidification along the edge of the Si strip. Thus, only one primary grain boundary perpendicular to the Si strip formed in the middle of the recessed region during ELC. The single-crystal-like Si TFTs fabricated on one-half of the recessed region are capable of excellent field-effect mobility of 640 cm(2)/V-s, with only minor deviation.
Sensitivity Enhancement of Ultraviolet Photodetectors With the Structure of p-NiO/Insulator-SiO2/n-ZnO Nanowires
(2015-08-01)
Li, Yu-Ren
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Wan, Chung-Yun
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Chang, Chia-Tsung
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Huang, Yu-Chih
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Tsai, Wan-Lin
A high-performance photodetector with the structure of NiO/SiO2/ZnO nanowires has been proposed. The devices with 6-nm-thick SiO2 exhibited a better rectification ratio (J(forward)/J(reverse)) of 246 at +/- 2 V, lower dark current density (J(dark)) of 3.5 x 10(-7) A/cm(2) at a reverse bias of 2 V, and superior ultraviolet (UV) sensitivity (I-UV/I-dark) of 16.23 than those without the SiO2 layer (J(forward)/J(reverse) = 44, Jdark = 4.7x10(-6) A/cm(2), and I-UV/I-dark = 5.5). The improved performance was mainly due to the ultrathin inserted SiO2 layer that builds a barrier height to minimize the transmission probability of low-energy carriers, leading to the enhancement of the UV sensing characteristics.
The pH Sensing Characteristics of the Extended-Gate Field-Effect Transistors of Multi-Walled Carbon-Nanotube Thin Film Using Low-Temperature Ultrasonic Spray Method
(2012-07-01)
Chien, Yun-Shan
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Yang, Po-Yu
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Tsai, Wan-Lin
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Li, Yu-Ren
;
Chou, Chia-Hsin
A novel, simple and low-temperature ultrasonic spray method was developed to fabricate the multi-walled carbon-nanotubes (MWCNTs) based extended-gate field-effect transistors (EGFETs) as the pH sensor. With an acid-treated process, the chemically functionalized two-dimensional MWCNT network could provide plenty of functional groups which exhibit hydrophilic property and serve as hydrogen sensing sites. For the first time, the EGFET using a MWCNT structure could achieve a wide sensing rage from pH = 1 to pH = 13. Furthermore, the pH sensitivity and linearity values of the CNT pH-EGFET devices were enhanced to 51.74 mV/pH and 0.9948 from pH = 1 to pH = 13 while the sprayed deposition reached 50 times. The sensing properties of hydrogen and hydroxyl ions show significantly dependent on the sprayed deposition times, morphologies, crystalline and chemical bonding of acid-treated MWCNT. These results demonstrate that the MWCNT-EGFETs are very promising for the applications in the pH and biomedical sensors.
Thickness effect of NiO on the performance of ultraviolet sensors with p-NiO/n-ZnO nanowire heterojunction structure
(2015-08-01)
Li, Yu-Ren
;
Wan, Chung-Yun
;
Chang, Chia-Tsung
;
Tsai, Wan-Lin
;
Huang, Yu-Chih
Based on the p-NiO/n-ZnO nanowire (NW) heterojunction structure, a high-performance ultraviolet (UV) sensor has been achieved in this work. The sputtered p-type NiO exhibited good coverage on the hydrothermally-grown n-type ZnO Nano-Wires (NW\'s). The devices with 250-nm-thick NiO obtained the highest UV light sensitivity (I-UV/I-Dark = 4.98; I-Visible/I-Dark = 3.82 biased at -2 V) under UV (lambda = 365 nm) intensity as low as 300 mu W/cm(2). Such p-n junction with thinner or thicker NiO layer led to worse UV detecting characteristics due to the fully-depleted NiO layer and larger series resistance, respectively. Furthermore, the N-2 annealing process can increase the UV light response and suppress the visible light response because of the reduced structural defects in ZnO NWs and the fewer interfacial defects (I-UV/I-Dark = 5.65; I-Visible/I-Dark = 1.35 biased at -2 V). (c) 2015 Elsevier Ltd. All rights reserved.