Browsing by Author "Lin, Jia-Chuan"

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Effect of Oxygen Annealing on the Ultraviolet Photoresponse of p-NiO-Nanoflower/n-ZnO-Nanowire Heterostructures
(2011-07-01)
Yang, Po-Yu
;
Wang, Jyh-Liang
;
Tsai, Wei-Chih
;
Wang, Shui-Jinn
;
Lin, Jia-Chuan
A transparent ultraviolet (UV) sensor using nanoheterojunctions (NHJs) composed of p-type NiO nanoflowers (NFs) and n-type ZnO nanowires (NWs) was prepared through a sequential low-temperature hydrothermal-growth process. The devices that were annealed in an oxygen (O(2)) ambient exhibited better rectification behavior (l(forward)/l(reverse) = 427), a lower forward threshold voltage (V(th) = 0.98 V), a lower leakage current (1.68 x 10(-5) A/cm(2)), and superior sensitivity (l(UV)/l(dark) = 57.8; l(visible)/l(dark) = 1.25) to UV light (lambda = 325 nm) than the unannealed devices. The remarkably improved device performances and optoelectronic characteristics of the annealed p-NiO-NF/n-ZnO-NW NHJs can be associated with their fewer structural defects, fewer interfacial defects, and better crystallinity. A stable and repeatable operation of dynamic photoresponse was also observed in the annealed devices. The excellent sensitivity and repeatable photoresponse to UV light of the hydrothermally grown p-NiO-NF/n-ZnO-NW NHJs annealed in a suitable O(2) ambient indicate that they can be applied to nano-integrated optoelectronic devices.
Field-Emission Characteristics of Al-Doped ZnO Nanostructures Hydrothermally Synthesized at Low Temperature
(2011-07-01)
Yang, Po-Yu
;
Wang, Jyh-Liang
;
Tsai, Wei-Chih
;
Wang, Shui-Jinn
;
Lin, Jia-Chuan
The aluminum-doped ZnO (AZO) nanostructures with different Al concentrations were synthesized on AZO/glass substrate via a simple hydrothermal growth method at a temperature as low as 85 degrees C. The morphologies, crystallinity, optical emission properties, and chemical bonding states of AZO nanostructures show evident dependence on the aluminum dosage. The morphologies of AZO nanostructures were changed from vertically aligned nanowires (NWs), and NWs coexisted with nanosheets (NSs), to complete NSs in respect of the Al-dosages of 0 similar to 3 at.%, 5 at.%, and 7 at.%, correspondingly. The undoped ZnO and lightly Al-doped AZO (<= 3 at.%) NWs are single-crystalline wurtzite structure. In contrast, heavily Al-doped AZO sample is polycrystalline. The AZO nanostructure with 3 at.% Al-dosages reveals the optimal crystallinity and less structural defects, reflecting the longest carrier lifetime and highest conductivity. Consequently, the field-emission characteristics of such an AZO emitter can exhibit the higher current density, larger field-enhancement factor (beta) of 3131, lower turn-on field of 2.17 V/mu m, and lower threshold field of 3.43 V/mu m.
High Field-Emission Stability of Offset-Thin-Film Transistor-Controlled Al-Doped Zinc Oxide Nanowires
(2011-04-01)
Yang, Po-Yu
;
Wang, Jyh-Liang
;
Tsai, Wei-Chih
;
Wang, Shui-Jinn
;
Lin, Jia-Chuan
Aluminum-doped zinc oxide (AZO) nanowire (NW) arrays incorporating an offset thin-film transistor (offset-TFT) have been proposed to achieve high field-emission (FE) stability. The AZO NW field emission arrays (FEAs) were hydrothermally grown at a low temperature of 85 degrees C. The uncontrolled AZO NW FEAs demonstrated superior FE characteristics (i.e., turn-on field of similar to 2.17 V/mu m and threshold field of similar to 3.43 V/mu m) compared with those of the conventional CNT FEAs grown at a temperature below 600 degrees C. However, uncontrolled AZO NW FEAs show a larger current fluctuation of 15.6%. Therefore, the offset-TFTs were used to control the AZO NW FEAs. Consequently, the fluctuation of AZO NW FEAs could be significantly reduced to less than 2%. This novel field emission device exhibits good emission stability, low-voltage controllability, low-temperature processing, and structural simplicity, making it promising for applications in flat panel displays. (C) 2011 The Japan Society of Applied Physics
Photoresponse of hydrothermally grown lateral ZnO nanowires
(2010-10-01)
Yang, Po-Yu
;
Wang, Jyh-Liang
;
Tsai, Wei-Chih
;
Wang, Shui-Jinn
;
Lin, Jia-Chuan
In this paper, a simple self-assembled lateral growth of ZnO nanowires (NWs) photodetector has been synthesized by a hydrothermal method at a temperature as low as 85 degrees C. The ZnO NWs exhibit single-crystalline wurtzite with elongated c-axis and can be selectively lateral self-assembled around the edges of ZnO seeding layer. The current of ZnO NWs is sensitive to the variation of ambient pressures, i.e. 4.47 mu A was decreased to 1.48 mu A with 5 V-bias as 1.1 x 10(-6) Torr changed to 760 Torr. accordingly. Moreover, the current voltage characteristics of ZnO NWs photodetectors can be evidently distinguished by UV illumination (i.e. lambda = 325 nm). The photocurrent of ZnO NWs with UV illumination is twice larger than dark current while the voltage biased at 5 V. Consequently, this faster photoresponse convinces that the hydrothermally grown lateral ZnO NWs devices have a fairly good for the fabrication of UV photodetectors. (C) 2010 Elsevier B.V. All rights reserved.
Simulation and analysis of metamorphic high electron mobility transistors
(2007-02-01)
Lin, Jia-Chuan
;
Yang, Po-Yu
;
Tsai, Wei-Chih
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光電工程學系
;
顯示科技研究所
In this paper, the metamorphic high electron mobility transistors (mHEMTs) are investigated numerically and compared with pseudomorphic high electron mobility transistors (pHEMTs). The two-dimensional device simulator, MEDICI, is used to solve the Poisson's equation and the electron/hole current continuity equations. The influences of delta-doping concentration and position, gate width, spacer thickness, etc. on the performances of HEMTs are explored. It shows clearly that mHEMTs have higher transconductances, drain currents and DC voltage swings than pHEMTs. (c) 2006 Elsevier Ltd. All rights reserved.
Structure design criteria of dual-channel high mobility electron transistors
(2007-01-01)
Lin, Jia-Chuan
;
Chen, Yu-Chieh
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Tsai, Wei-Chih
;
Yang, Po-Yu
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光電工程學系
The design criteria of dual-channel high electron mobility transistor (DHEMT) are proposed in this study. 8-Doped In(0.52)Al(0.48)As/ In(0.53)Ga(0.47)As/InP material systems are concentrated in this article. The DHEMT structures are explored numerically and compared with conventional single-channel high electron mobility transistor (SHEMT) structures. Some criteria of doping concentration and layer structure design are proposed. The simulation results reveal that DHEMT has a larger voltage swing, a lower gate leakage current, a better carrier confinement, a higher density of two-dimensional electron gas (2DEG) and an excellent transconductance than SHENIT. (c) 2006 Elsevier Ltd. All rights reserved.