Browsing by Author "Chen, Jenn-Fang"

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A novel dilute antimony channel In0.2Ga0.8AsSb/GaAs HEMT
(2007-02-01)
Su, Ke-Hua
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Hsu, Wei-Chou
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Lee, Ching-Sung
;
Wu, Tsung-Yeh
;
Wu, Yue-Han
This letter reports, for the first time, a high-electron mobility. transistor (HEMT) using A dilute antimony In0.2Ga0.8AsSb channel, which is grown by a molecular-beam epitaxy system. The interfacial quality within the InGaAsSb/GaAs quantum well of the HEMT device was effectively improved by introducing the surfactantlike Sb atoms during the growth of the InGaAs layer. The improved heterostructural quality and electron transport properties have also been verified by various surface characterization techniques. In comparison, the proposed HEMT with (without) the incorporation of Sb atoms has demonstrated the maximum extrinsic transconductance g(m,max) of 227 (180) mS/mm, a drain saturation current density I-DSS of 218 (170) mA/mm, a gate-voltage swing of 1.215 (1.15) V, a cutoff frequency f(T) of 25 (20.6) GHz, and the maximum oscillation frequency f(max) of 28.3 (25.6) GHz at 300 K with gate dimensions of 1.2 x 200 mu m(2).
Ab initio molecular orbital calculation of 1,3,5-triazine derivatives as hosts for phosphorescent organic light emitting devices
(2005)
Chu, Ta-Ya
;
Ho, Meng-Huan
;
Chen, Jenn-Fang
;
Chen, Chin H.
;
電子物理學系
Novel triplet host materials 2,4,6-tris (diarylamino)-1,3,5-triazine derivatives (TRZ1-TRZ4) have been reported and from which TRZ2 as a host for Ir(ppy)(3) was particularly useful in producing high efficiency phosphorescent organic light emitting diodes (OLEDs). This paper reports the molecular orbital and energy level of these derivatives determined by ab initio calculation. The calculated triplet bandgap energy of TRZ1 has been found to be larger than that of TRZ2.
Analysis of InAsN quantum dots by transmission electron microscopy and photoluminescence
(2008-10-01)
Hsu, Chiung-Chih
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Hsu, Ray-Quen
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Wu, Yue-Han
;
Chi, Tung-Wei
;
Chiang, Chen-Hao
Quantum dots (QDs) have great potential in optical fiber communication applications were widely recognized. The structure of molecular beam epitaxy (MBE) grew InAsN QDs were investigated by transmission electron microscopy (TEM) and measured their optical properties by photoluminescence (PL). TEM images show that the InAsN QDs are irregular or oval shaped. Some of the InAsN QDs are observed to have defects, such as dislocations at or near the surface in contrast to InAs QDs, which appear to be defect free. PL results for InAsN QDs showed a red-shifted emission peak. In addition, the InAsN emission peak is broader than InAs QDs, which supports the TEM observation that the size distribution of the InAsN QDs is more random than InAs QDs. The results show that the addition of nitrogen to InAs QDs leads to a decrease in the average size of the QDs, bring changes in the QD's shape, compositional distribution, and optical properties. (C) 2008 Published by Elsevier B.V.
Comparative study of single and multiemissive layers in inverted white organic light-emitting devices
(2006-09-11)
Chu, Ta-Ya
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Chen, Jenn-Fang
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Chen, Szu-Yi
;
Chen, Chin H.
;
電子物理學系
The authors have fabricated and compared highly efficient inverted white organic light-emitting devices (WOLEDs) with a single emission layer (SEL) and with a multiemission layer (MEL). The efficiency levels of the WOLEDs with a SEL and a MEL achieved 13.0 cd/A, 10.6 lm/W and 11.3 cd/A, 7.3 lm/W, respectively. The projected half lifetime of a SEL device under an initial luminance of 400 cd/m(2) is expected to be over 34 000 h, which is five times better than that of a MEL device of 6350 h. The Commission International de l'Eclairage coordinates of a SEL device are not affected by aging. (c) 2006 American Institute of Physics.
Dark current suppression of amorphous selenium based photosensors by the ZnO hole blocking layer
(2014-05-01)
Yu, Tung-Yuan
;
Pan, Fu-Ming
;
Chang, Cheng-Yi
;
Hu, Tien
;
Chen, Jenn-Fang
To study the influence of defects in the hole blocking layer (HBL) on the dark current of amorphous selenium (a-Se) based photosensors, we prepared ZnO thin films by reactive sputter deposition (RSD) for the use as the HBL of the photosensors. The ZnO HBL layers prepared with different oxygen flow rates were characterized by X-ray photoelectron spectroscopy, Raman scattering analysis and photoluminescence, indicating that the density of oxygen vacancies in the ZnO thin films is significantly affected by the oxygen flow rate. The deep level transient spectroscopy measurement reveals two hole trap levels present in the RSD deposited ZnO thin films; one is at 0.94 eV and the other at 0.24 eV above the valence band edge. The electrical performance of the a-Se photosensor is largely influenced by the amount of oxygen vacancies in the ZnO thin film. The a-Se photosensor with the ZnO HBL of the most oxygen vacancies has the lowest dark current and demonstrates the highest breakdown field. (C) 2014 Elsevier B.V. All rights reserved.
Development of stable micro-crystalline silicon AMLCD
(2007-01-01)
Chang, Chan-Ching
;
Chen, Chih-Hsien
;
Peng, Ya-Hui
;
Lee, Yeong-Shyang
;
Hou, Chih-Yuan
Bottom-gate microcrystalline silicon thin film transistors (mu c-Si TFTs) have been produced by the radio frequency glow discharge technique using three different plasma treatment on the interface between microcrystalline and SiN layers. Our first microcrystalline silicon TFTs have better stability at high temperature stress.
Dielectrophoretic placement of quasi-zero-, one-, and two-dimensional nanomaterials into nanogap for electrical characterizations
(2012-08-01)
Lin, Yen-Fu
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Chiu, Shao-Chien
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Wang, Sheng-Tsung
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Fu, Sheng-Kai
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Chen, Chien-Hsiang
DEP is one of promising techniques for positioning nanomaterials into the desirable location for nanoelectronic applications. In contrast, the lithography technique is commonly used to make ultra-thin conducting wires and narrow gaps but, due to the limit of patterning resolution, it is not feasible to make electrical contacts on ultra-small nanomaterials for a bottom-up device fabrication. Thus, integrating the lithography and dielectrophoresis, a real bottom-up fabrication can be achieved. In this work, the device with the nanogap in between two nanofinger-electrodes is made using electron-beam lithography from top down and the ultra-small nanomaterials, such as colloidal PbSe quantum dots, polyaniline nanofibers, and reduced-graphene-oxide flakes, are placed in the nanogap by DEP from bottom up. The threshold electric field for the DEP placement of PbSe nanocrystals was roughly estimated to be about 8.3 x 104 V/cm under our experimental configuration. After the DEP process, several procedures for reducing contact resistances are attempted and measurements of intrinsic electron transport in versatile nanomaterials are performed. It is experimentally confirmed that electron transport in both PbSe nanocrystal arrays and polyaniline nanofibers agrees well with Prof. Ping Sheng's model of granular metallic conduction. In addition, electron transport in reduced-graphene-oxide flakes follows Mott's 2D variable-range-hopping model. This study illustrates an integration of the electron-beam lithography and the DEP techniques for a precise manipulation of nanomaterials into electronic circuits for characterization of intrinsic properties.
"Dielectrophoretic placement of quasi-zero-, one-, and two-dimensional nanomaterials into nanogap for electrical characterizations"
(2012-08-01)
Lin, Yen-Fu
;
Chiu, Shao-Chien
;
Wang, Sheng-Tsung
;
Fu, Sheng-Kai
;
Chen, Chien-Hsiang
"DEP is one of promising techniques for positioning nanomaterials into the desirable location for nanoelectronic applications. In contrast, the lithography technique is commonly used to make ultra-thin conducting wires and narrow gaps but, due to the limit of patterning resolution, it is not feasible to make electrical contacts on ultra-small nanomaterials for a bottom-up device fabrication. Thus, integrating the lithography and dielectrophoresis, a real bottom-up fabrication can be achieved. In this work, the device with the nanogap in between two nanofinger-electrodes is made using electron-beam lithography from top down and the ultra-small nanomaterials, such as colloidal PbSe quantum dots, polyaniline nanofibers, and reduced-graphene-oxide flakes, are placed in the nanogap by DEP from bottom up. The threshold electric field for the DEP placement of PbSe nanocrystals was roughly estimated to be about 8.3 x 104 V/cm under our experimental configuration. After the DEP process, several procedures for reducing contact resistances are attempted and measurements of intrinsic electron transport in versatile nanomaterials are performed. It is experimentally confirmed that electron transport in both PbSe nanocrystal arrays and polyaniline nanofibers agrees well with Prof. Ping Sheng's model of granular metallic conduction. In addition, electron transport in reduced-graphene-oxide flakes follows Mott's 2D variable-range-hopping model. This study illustrates an integration of the electron-beam lithography and the DEP techniques for a precise manipulation of nanomaterials into electronic circuits for characterization of intrinsic properties."
Effects of cross-sectional area on the tunneling-junction array in octahedral PbSe colloidal-nanocrystal solids
(2013)
Chiu, Shao-Chien
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Jhang, Jia-Sin
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Chen, Jenn-Fang
;
Fang, Jiye
;
Jian, Wen-Bin
Octahedral PbSe colloidal nanocrystals (NCs) are used to assemble a solid. Because of the special feature of the apexes of the octahedrons, the cross-sectional area of the inter-dot tunneling junctions is much smaller than that formed between spherical NCs. The inter-dot separation between NCs is easily adjusted by mild thermal treatment. Like a spherical NC-solid, the resistance of the octahedral NC-solid is exponentially dependent on the inter-dot separation. On the contrary, due to the difference in the cross-sectional area between the NCs, electron transport in the octahedral NC-solid does not follow the same model used for the explanation of electron transport in a spherical NC-solid. Through analyses of current-voltage and resistance-temperature behaviors, we have confirmed that the model of fluctuation-induced tunneling conduction fits very well with all of the data and explains the variation in the electrical properties of octahedral PbSe colloidal NC-solids after thermal annealing.
Efficient electron injection in organic light-emitting diodes using dipotassium phthalate as n-type dopant
(2008)
Ho, Meng-Huan
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Hsieh, Ming-Ta
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Chen, Jenn-Fang
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Hwang, Shiao-Wen
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Chen, Chin H.
An efficient n-doped electron transport layer composed of 4,7-diphenyl- 1, 10-phenanthroline (BPhen) and dipotassium phthalate (PAK2) has been developed. By temperature-dependent admittance spectroscopy, the incorporation of PAK2 into BPhen is found to increase electron concentration in BPhen laYer, resulting in raising the Fermi-level to similar to 0.5 eV below its LUMO which further enhances the efficiency of electron injection from Al cathode. When this n-doped layer is adopted in OLED device, the green Alq(3) device can achieve a current efficiency of 3.6 cd/A and a power efficiency of 2.1 lm/W at 20 mA/cm(2) and lower drive voltage of 5.3 V.
Electrical characterization of bathophenanthroline doped with dipotassium phthalate
(2007)
Hsieh, Ming-Ta
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Chang, Chan-Ching
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Chen, Jenn-Fang
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Ho, Meng-Huan
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Chen, Teng-Ming
Bathophenanthroline (BPhen) doped with dipotassium phthalate (PAK2) was electrically characterized using current-voltage (I-V) and temperature-dependent admittance spectroscopy measurements which demonstrates that the incorporation of PAK2 into BPhen can increase the electron concentration of the BPhen layer resulting in the transformation of the Fermi-level from deep to shallow (around 0.5 eV below LUMO band) and Accordingly, PAK2 is an alternative n-type organic dopant for n-type doping device.
Electrical characterization of organic light-emitting diodes using dipotassium phthalate as n-type dopant
(2008-08-25)
Ho, Meng-Huan
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Hsieh, Ming-Ta
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Chen, Teng-Ming
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Chen, Jenn-Fang
;
Hwang, Shiao-Wen
An efficient n-doped electron transport layer composed of 4,7-diphenyl-1,10-phenanthroline (BPhen) and dipotassium phthalate (PAK2) has been developed. By temperature-dependent admittance spectroscopy, the incorporation of PAK2 into BPhen is found to raise the Fermi level from 1.7 eV to only around 0.5 eV below BPhen's lowest unoccupied molecular orbital, which further enhances the efficiency of electron injection from an A1 cathode. When this n-doped layer is adopted in an organic light-emitting diode device, the green fluorescent 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H, 5H, 11H-benzo[l]-pyrano[6,7,8-ij]quinolizin-11-one doped device can achieve a current efficiency of 16 cd/A and a power efficiency of 10.9 lm/W at 1000 cd/m(2). (C) 2008 American Institute of Physics.
Electrical Properties of Metal-Silicon Nitride-Hydrogenated Amorphous Silicon Capacitor Elucidated Using Admittance Spectroscopy
(2008-12-01)
Hsieh, Ming-Ta
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Chen, Jenn-Fang
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Yen, Kuo-Hsi
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Zan, Hsiao-Wen
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Chang, Chan-Ching
Detailed admittance spectroscopy was performed on a metal-silicon nitride-hydrogenated amorphous silicon (MIAS) structure. On the basis of the properties of hydrogenated amorphous silicon (a-Si:H), three simplified equivalent circuit models under various operating conditions (accumulation, depletion and full depletion) are presented along with an alternative direct measurement method at room temperature. Admittance spectroscopy shows that the interface states density between silicon nitride (SiN(x)) and a-Si:H can be determined from the depletion equivalent circuit model. The resisivity and activation energy of a-Si:H can also be obtained using the accumulation and depletion equivalent circuit models. These models can be employed easily to monitor the fabrication parameters of thin-films transistors (TFTs) and to accurately and directly obtain the capacitance model parameters of TFTs. [DOI: 10.1143/JJAP.47.8714]
Electron Emission Properties of GaAsN/GaAs Quantum Well Containing N-Related Localized States: The Influence of Illuminance
(2012-02-01)
Hsieh, Meng-Chien
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Wang, Jia-Feng
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Wang, Yu-Shou
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Yang, Cheng-Hong
;
Chiang, Chen-Hao
This study elucidates the electron emission properties of GaAsN/GaAs quantum well containing N-related localized states under illumination. The N-related localized states in a GaAsN quantum well (QW) are identified as both optical and electrical electron trap states. The mechanisms for the responses of current-voltage (I-V) measurement under illumination and photocapacitance are investigated. N-related localized states in GaAsN QW can extend response range and response sensitivity on photocapacitance, and produce an additional current path for photo-generated electron-hole pairs. Furthermore, exactly how illumination influences the electron emission rate of GaAsN QW electron state is examined. The electron emission rate of GaAsN QW electron state can be modulated by different incident photon energy, which is due to the modulation of depletion width of the bottom GaAs. (C) 2012 The Japan Society of Applied Physics
Electron Emission Properties of Nitrogen-Induced Localized Defects in InAsN/GaAs Quantum Dots
(2011-11-01)
Yang, Cheng-Hong
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Hsieh, Meng-Chien
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Wu, Chia-Wei
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Chang, Yen-Ting
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Wu, Yue-Han
The electron-emission properties of nitrogen-induced (N-induced) localized defects in InAsN/GaAs quantum dots (QDs) are investigated in detail by capacitance-voltage (C-V) profiling and bias-dependent deep-level transient spectroscopy (DLTS). The incorporation of nitrogen (N) into InAs QDs is shown to produce localized defects near QDs and threading-dislocation-related defects in the top GaAs layer. The threading dislocation is associated with an electron-emission energy of approximately 0.648 eV and emission from the sample surface toward the QDs. The electron-emission energy from the QDs associated with the localized defects increases from 0.19 to 0.36 eV, indicating that both types of defect near QDs have low electron emission energies. Therefore, the change in emission energy is attributable to the defects across the QD interface where a band offset exists. The C-V profile at 300 K shows extended carrier depletion near the QDs. As ac frequency increases, an electron-emission peak emerges at the QDs; this peak is followed by another prominent peak, suggesting that the localized defect that is responsible for this latter peak has an energy below the QD electron ground state. On the basis of a C-V profile simulation, this defect is located at the QD at the observed emission energy below the GaAs conduction band, 360 meV. A comparison with InAsN QD and strain relaxation InAs QD samples reveals that the localized defect arises from a nitrogen alloy fluctuation in the QD. The energy location of this defect reveals a possibility that incorporated N is associated with a particular mode. (C) 2011 The Japan Society of Applied Physics
Enhancing threshold voltage of AlGaN/GaN high electron mobility transistors by nano rod structure: From depletion mode to enhancement mode
(2012-09-10)
Xuan, Rong
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Kuo, Wei-Hong
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Hu, Chih-Wei
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Lin, Suh-Fang
;
Chen, Jenn-Fang
This paper presents an approach in fabricating normally off AlGaN/GaN high electron mobility transistors (HEMTs). The fabrication technique was based on the carbon-doped GaN epitaxy layers on silicon substrate and the nano rod structure of the gate region in AlGaN/GaN HEMTs. Using this method, the threshold voltage of AlGaN/GaN HEMTs can be shifted from -2 V in a conventional depletion-mode (D-mode) AlGaN/GaN HEMT to 2 V in an enhancement-mode (E-mode) AlGaN/GaN HEMT. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752113]
Evolution of carrier distribution and defects in InGaAsN/GaAs quantum wells with composition fluctuation
(2006-07-01)
Chen, Jenn-Fang
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Hsiao, Ru-Shang
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Hsieh, Pei-Chen
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Chen, Yu-Chih
;
Wang, Jyh-Shyang
Carrier distribution and defect induction in In0.34Ga0.66As0.98N0.02/GaAs-single quantum wells grown by molecular beam epitaxy at low growth rates are investigated by frequency-dependent capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS). The C-V studies show that lowering the growth rate of the InGaAsN layer splits the carrier accumulation in the well into a central and two side peaks with different frequency dispersions. The DLTS studies show that a continuum of states (0-0.083eV) and a,deep trap at 0.21-0.25eV are responsible for the central and the side peaks, respectively. A comparison with photoluminescence (PL) spectra shows that these defects are induced by composition fluctuation. Lowering the growth rate degrades composition fluctuation by segregating the material into an InGaAsN phase and an N-depleted phase. Post-growth annealing can remove the deep trap and improve the InGaAsN emission, confirming that the deep trap degrades the InGaAsN phase. The feature of the continuum of states suggests that it may be the structural defects associated with lattice expansion or localized states introduced by composition fluctuation.
High-Efficiency Inverted Transparent Blue Organic Light-Emitting Devices
(2006)
Chen, Szu-Yi
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Chu, Ta-Ya
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Chen, Chao-Jung
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Chen, Jenn-Fang
;
Chen, Chin H.
We report efficient inverted transparent blue OLEDs (ITOED) with an hole injection layer prepared by co-evaporation of WO3 with NPB, which achieved a total current efficiency 0 10.7 cd/A at 20 mA/cm(2) with light emits from both ITO bottom cathode and Au top anode in about 3:1 ratio.
Highly efficient and stable inverted bottom-emission organic light emitting devices
(2006-07-31)
Chu, Ta-Ya
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Chen, Jenn-Fang
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Chen, Szu-Yi
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Chen, Chao-Jung
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Chen, Chin H.
The authors report the development of highly efficient and stable C545T doped green fluorescent Alq(3) inverted bottom-emission organic light emitting device (OLED), with a device configuration of ITO/Mg/Cs(2)O:Bphen/Alq(3)/C545T:Alq(3)/NPB/WO(3)/Al, that achieved a maximum current efficiency of 23.7 cd/A and a power efficiency of 12.4 lm/W which are two times better than those of the conventional OLED. At a brightness level of 100 cd/m(2), the device required driving current density only as low as 0.5 mA/cm(2) at a driving voltage of only 5.0 V and its half-lifetime T(1/2) in excess of 104 000 h. (c) 2006 American Institute of Physics.
Highly power efficient organic light-emitting diodes with a p-doping layer
(2006-12-18)
Chang, Chan-Ching
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Hsieh, Ming-Ta
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Chen, Jenn-Fang
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Hwang, Shiao-Wen
;
Chen, Chin H.
In this letter, the authors demonstrate p-i-n organic light-emitting diodes (OLEDs) incorporating a p-doped transport layer which comprises tungsten oxide (WO3) and 4,4('),4(')-tris(N-(2-naphthyl)-N-phenyl-amino)triphenylamine (2-TNATA) to replace the volatile tetrafluro-tetracyanoquinodimethane. The authors propose the 2-TNATA:WO3 composition functions as a p-doping layer which significantly improves hole injection and conductivity of the device that leads to the fabrication of tris(8-quinolinolato)aluminum based p-i-n OLEDs with long lifetime, low driving voltage (3.1 V), and high power efficiency (3.5 lm/W) at 100 cd/m(2). (c) 2006 American Institute of Physics.