Browsing by Author "Shieh, Jiann"

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Broadband and wide angle antireflection of sub-20 nm GaAs nanograss
(2012-06-01)
Ravipati, Srikanth
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Shieh, Jiann
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Ko, Fu-Hsiang
;
Yu, Chen-Chieh
;
Chen, Hsuen-Li
GaAs nanograss with diameters of less than 20 nm has been fabricated using a simple, one-step, maskless plasma etching-based approach. GaAs nanograss exhibits remarkable broadband antireflection properties, which arise from the graded refractive index between air and the GaAs substrate by the nanograss layer. Moreover, GaAs nanograss shows less sensitivity to transverse electric polarized light and transverse magnetic polarized light over a wide range of incident angles compared to the strong variation in a bare GaAs substrate. These effects show that sub-20 nm GaAs nanograss with lengths of approximately 200 nm has an enhanced absorption of 98-100% when the incident energy is larger than the GaAs bandgap (lambda = 240-873 nm) and an enhanced absorption of 72-98% when the incident energy is less than the bandgap (lambda = 873-2400 nm). Our simple, one-step, and maskless plasma etching method opens a promising approach for the direct implementation of broad omnidirectional antireflective surfaces on solar cells and various optoelectronic devices to improve device performance.
Broadband antireflection and field emission properties of TiN-coated Si-nanopillars
(2014-08-21)
Chang, Yuan-Ming
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Ravipati, Srikanth
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Kao, Pin-Hsu
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Shieh, Jiann
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Ko, Fu-Hsiang
Broadband antireflection and field emission characteristics of silicon nanopillars (Si-NPs) fabricated by self-masking dry etching in hydrogen-containing plasma were systematically investigated. In particular, the effects of ultrathin (5-20 nm) titanium nitride (TiN) films deposited on Si-NPs by atomic layer deposition (ALD) on the optoelectronic properties were explored. The results showed that by coating the Si-NPs with a thin layer of TiN the antirefiection capability of pristine Si-NPs can be significantly improved, especially in the wavelength range of 1000-1500 nm. The enhanced field emission characteristics of these TiN/Si-NP heterostructures suggest that, in addition to the reflectance suppression in the long wavelength range arising from the strong wavelength-dependent refractive index of TiN, the TiN-coating may have also significantly modified the effective work function at the TiN/Si interface as well.
Electrode dependence of filament formation in HfO(2) resistive-switching memory
(2011-04-15)
Lin, Kuan-Liang
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Hou, Tuo-Hung
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Shieh, Jiann
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Lin, Jun-Hung
;
Chou, Cheng-Tung
This study investigates bipolar and nonpolar resistive-switching of HfO(2) with various metal electrodes. Supported by convincing physical and electrical evidence, it is our contention that the composition of conducting filaments in HfO(2) strongly depends upon the metal electrodes. Nonpolar resistive-switching with the Ni electrode is attributed to the migration of metal cations and the corresponding electrochemical metallization. Conversely, oxygen-deficient filaments induced by anion migration are responsible for bipolar resistive-switching. It was also found that the characteristic nature of the conducting filaments influences many aspects of switching characteristics, including the switching power, cycling variations, and retention at elevated temperatures. (C) 2011 American Institute of Physics. [doi:10.1063/1.3567915]
Electrode dependence of filament formation in HfO2 resistive-switching memory
(2011-04-15)
Lin, Kuan-Liang
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Hou, Tuo-Hung
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Shieh, Jiann
;
Lin, Jun-Hung
;
Chou, Cheng-Tung
This study investigates bipolar and nonpolar resistive-switching of HfO2 with various metal electrodes. Supported by convincing physical and electrical evidence, it is our contention that the composition of conducting filaments in HfO2 strongly depends upon the metal electrodes. Nonpolar resistive-switching with the Ni electrode is attributed to the migration of metal cations and the corresponding electrochemical metallization. Conversely, oxygen-deficient filaments induced by anion migration are responsible for bipolar resistive-switching. It was also found that the characteristic nature of the conducting filaments influences many aspects of switching characteristics, including the switching power, cycling variations, and retention at elevated temperatures. (C) 2011 American Institute of Physics. [doi:10.1063/1.3567915]
Enhanced Free Exciton and Direct Band-Edge Emissions at Room Temperature in Ultrathin ZnO Films Grown on Si Nanopillars by Atomic Layer Deposition
(2011-11-01)
Chang, Yuan-Ming
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Shieh, Jiann
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Chu, Pei-Yuan
;
Lee, Hsin-Yi
;
Lin, Chih-Ming
Room-temperature ultraviolet (UV) luminescence was investigated for the atomic layer deposited ZnO films grown on silicon nanopillars (Si-NPs) fabricated by self-masking dry etching in hydrogen-containing plasma. For films deposited at 200 degrees C, an intensive UV emission corresponding to free-exciton recombination (similar to 3.31 eV) was observed with a nearly complete suppression of the defect-associated broad visible range emission peak. On the other hand, for ZnO films grown at 25 degrees C, albeit the appearance of the defect-associated visible emission, the UV emission peak was observed to shift by similar to 60 meV to near the direct band edge (3.37 eV) recombination emission. The high-resolution transmission electron microscopy (HRTEM) showed that the ZnO films obtained at 25 degrees C were consisting of ZnO nanocrystals with a mean radius of 2 nm embedded in a largely amorphous matrix. Because the Bohr radius of free-exictons in bulk ZnO is similar to 2.3 nm, the size confinement effect may have occurred and resulted in the observed direct band edge electron-hole recombination. Additionally, the results also demonstrate order of magnitude enhancement in emission efficiency for the ZnO/Si-NP structure, as compared to that of ZnO directly deposited on Si substrate under the same conditions.
Evolution of RESET current and filament morphology in low-power HfO(2) unipolar resistive switching memory
(2011-03-07)
Hou, Tuo-Hung
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Lin, Kuan-Liang
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Shieh, Jiann
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Lin, Jun-Hung
;
Chou, Cheng-Tung
Reduction in RESET current is crucial for future high-density resistive-switching memory. We have reported a unipolar-switching Ni/HfO(2)/Si structure with low RESET current of 50 mu A and RESET power of 30 mu W. In addition, a unique cycling evolution of RESET current across more than two orders of magnitude allows us to probe into the evolvement of filament morphology at nanoscale, using a simple yet quantitative model. Filament morphology was found to depend strongly on the charge-dissipation current proportional to the powers of SET voltage. Moreover, the formation of inactive semiconductive filaments plays an important role in the reduction in RESET current. (C) 2011 American Institute of Physics. [doi:10.1063/1.3565239]
Evolution of RESET current and filament morphology in low-power HfO2 unipolar resistive switching memory
(2011-03-07)
Hou, Tuo-Hung
;
Lin, Kuan-Liang
;
Shieh, Jiann
;
Lin, Jun-Hung
;
Chou, Cheng-Tung
Reduction in RESET current is crucial for future high-density resistive-switching memory. We have reported a unipolar-switching Ni/HfO2/Si structure with low RESET current of 50 mu A and RESET power of 30 mu W. In addition, a unique cycling evolution of RESET current across more than two orders of magnitude allows us to probe into the evolvement of filament morphology at nanoscale, using a simple yet quantitative model. Filament morphology was found to depend strongly on the charge-dissipation current proportional to the powers of SET voltage. Moreover, the formation of inactive semiconductive filaments plays an important role in the reduction in RESET current. (C) 2011 American Institute of Physics. [doi:10.1063/1.3565239]
Fabrication and enhanced field emission properties of novel silicon nanostructures
(2010-12-01)
Ravipati, Srikanth
;
Kuo, Chang-Jung
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Shieh, Jiann
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Chou, Cheng-Tung
;
Ko, Fu-Hsiang
We reported the fabrication and the field emission properties of two-tier novel silicon nanostructures. First, silicon nanopillars with ordered high aspect ratio were achieved by using conventional lithographic techniques to act as the field emission sources. Second, sharp-edged well-aligned silicon nanograss was fabricated on top of the nanopillars by means of hydrogen plasma dry etching to induce the field emission characteristics. The turn-on fields were obtained as 10.5 and 14.4 V/mu m under current density of 0.01 mA/cm(2) for two-tier patterns separated by respective 5 mu m and 2 mu m spaces. The excellent field emission property from these novel nanostructures exhibited a great potential as high-performance field emitter arrays towards future nanoelectronic devices. (C) 2010 Elsevier Ltd. All rights reserved.
Plasma-made silicon nanograss and related nanostructures
(2011-05-04)
Shieh, Jiann
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Ravipati, Srikanth
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Ko, Fu-Hsiang
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Ostrikov, Kostya (Ken)
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材料科學與工程學系
Plasma-made nanostructures show outstanding potential for applications in nanotechnology. This paper provides a concise overview on the progress of plasma-based synthesis and applications of silicon nanograss and related nanostructures. The materials described here include black silicon, Si nanotips produced using a self-masking technique as well as self-organized silicon nanocones and nanograss. The distinctive features of the Si nanograss, two-tier hierarchical and tilted nanograss structures are discussed. Specific applications based on the unique features of the silicon nanograss are also presented.
Subwavelength Antireflective Si Nanostructures Fabricated by Using the Self-Assembled Silver Metal-Nanomask
(2011-05-12)
Chang, Yuan-Ming
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Shieh, Jiann
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Juang, Jenh-Yih
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電子物理學系
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Department of Electrophysics
We report a lithography-free approach for fabricating silicon nanopillars (Si-NPs) and biomimetics porous silicon (P-Si) with excellent antireflective properties. The self-assembled silver nanostructures (nanoislands and disordered nanogrids) were formed via the Volmer-Weber (island growth) mode during the deposition process, which, in turn, serve as a metal-nanomask for the subsequent dry etching process carried out for fabricating the Si-NPs and P-Si on Si substrates. Reflectivity of about 0.65% was obtained over the spectral region ranging from deep-ultraviolet to infrared light (300-1000 nm). The remarkable antireflective characteristics obtained are attributed to the drastic decrease of effective index of refraction and the enhanced matching effect between air and substrate resulting from the Si nanostructures and suggesting an interesting alternative route for producing nanostructures that might be useful for photovoltaic applications.
Switching Mode and Mechanism in Binary Oxide Resistive Random Access Memory Using Ni Electrode
(2013-03-01)
Lin, Kuan-Liang
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Hou, Tuo-Hung
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Lee, Yao-Jen
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Chang, Jhe-Wei
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Lin, Jun-Hung
Resistive-switching (RS) modes in different CMOS-compatible binary oxides have been shown to be governed by the interplay with the Ni top electrode. Unipolar RS and metallic low-resistance state in polycrystalline HfO2 and ZrO2 are distinct from the preferential bipolar RS and semiconductive low-resistance state in amorphous Al2O3 and SiO2. Backside secondary ion mass spectrometry (SIMS) has shown the formation of Ni filaments in HfO2, in contrast to the formation of oxygen-vacancy filaments in Al2O3. The differences have been explained by strong dependence of Ni migration on the oxide crystallinity. Additionally, the RS mode can be further tailored using bilayer structures. The oxide layer next to the Si bottom electrode and its tendency of forming Ni filaments play significant roles in unipolar RS in the bilayer structures, in support of the conical-shape Ni filament model where the connecting and rupture of filaments for unipolar RS occur at the smallest diameter near the bottom electrodes. (c) 2013 The Japan Society of Applied Physics
Ultralow Reflection from a-Si Nanograss/Si Nanofrustum Double Layers
(2013-03-25)
Ravipati, Srikanth
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Shieh, Jiann
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Ko, Fu-Hsiang
;
Yu, Chen-Chieh
;
Chen, Hsuen-Li
A double-layer nanostructure comprising amorphous Si nanograss on top of Si nanofrustums (NFs) with a total height of 680 nm exhibits ultralow reflection. Almost near-unity absorption and near-zero reflectance result in this layered nanostructure, over a broad range of wavelengths and a wide range of angles of incidence, due to the low packing density of a-Si and the smooth transition of the refractive index from the air to the Si substrate across both the nanograss and NF layers.