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GaN-based vertical-cavity surface-emitting laser incorporating a TiO2 high-index-contrast grating
(2020-01-01)
Chang, Tsu-Chi
;
Hashemi, Ehsan
;
Bengtsson, Jorgen
;
Gustavsson, Johan
;
Haglund, Asa
We demonstrate the first electrically injected GaN-based VCSEL with a TiO2 high-contrast grating (HCG) as the top mirror. The TiO2-HCG rested directly on the n-GaN without an airgap for mechanical stability. A VCSEL with an aperture diameter of 10 mu m had a threshold current of 25 mA under pulsed operation at room temperature. Multiple longitudinal modes coexist around 400 nm, each TM-polarized with a linewidth of 0.5 nm (spectral resolution limited). This first demonstration of a TiO2-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as post-growth setting of resonance wavelength.
Large Photoresponsivity in the Amorphous-TiO2/SrRuO(3)Heterostructure
(1970-01-01)
Liu, Heng-Jui
;
Huang, Chin-Han
;
Chen, Cheng-Ying
;
Hsiao, Sheng-Wei
;
Chen, You-Sheng
Thin-film heterostructures are effective in enhancing the performance or triggering novel physical phenomena of optoelectronic applications. For example, the epitaxial heterostructures of ultraviolet-light-sensitive TiO(2)with metallic SrRuO(3)can acquire visible-light functionalities using the hot carrier injection mechanism. Therefore, the TiO2/SrRuO(3)heterostructure system has recently attracted increasing interest. Herein, the amorphous-TiO2/SrRuO(3)heterostructure is fabricated and compared to the epitaxial TiO2/SrRuO3. As opposed to the occurrence of the visible-light photovoltaic effect in the epitaxial TiO2/SrRuO3, the amorphous-TiO2/SrRuO(3)heterostructure herein exhibits different optoelectronic functionality, specifically the photoresistor behavior. The amorphous-TiO2/SrRuO(3)heterostructure achieves a photoresponsivity of 6.56 A W(-1)at 1 V. Such a performance is hardly obtained in typical oxide-based photoresistors. The analyses of the crystalline and electronic structures show that it is due to the defect-induced high electron doping in the amorphous TiO(2)with hot carrier injection mechanism. This study discusses the correlation between the hot carrier injection and band diagram, which provides more degrees of freedom in designing potential optoelectronic devices.
Electrically Injected GaN-Based Vertical-Cavity Surface-Emitting Lasers with TiO2 High-Index-Contrast Grating Reflectors
(2020-04-15)
Chang, Tsu-Chi
;
Hashemi, Ehsan
;
Hong, Kuo-Bin
;
Bengtsson, Jorgen
;
Gustaysson, Johan
We demonstrate the first electrically injected GaNbased vertical-cavity surface-emitting lasers (VCSELs) with a TiO2 high-index-contrast grating (HCG) as the top mirror. Replacing the top distributed Bragg reflector (DBR) with an HCG offers substantial thickness reduction, polarization-pinning, and setting of the resonance wavelength by the grating parameters. Conventional HCGs are usually suspended in the low refractive index material, such as air, in order to create the largest refractive index contrast. However, the mechanical stability of such structures can be questioned and creating free-hanging GaN-membrane on top of GaN is problematic. We have therefore fabricated TiO2-HCGs resting directly on GaN without an air-gap. No DBR layers are used below the HCG to boost the reflectivity. A VCSEL with an aperture diameter of 10 mu m shows a threshold current of 25 mA under pulsed operation at room temperature. The lasing modes locate around 400 nm and are transversely electrically -polarized with a line width of 0.5 nm. The full-width half-maximum beam divergence is 10 degrees. This demonstration of a TiO2-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as postgrowth setting of the resonance wavelength.
Fabrication of TiO2-coated nanostructured Ni foams for improved mechanical properties
(2020-02-15)
Hung, Pei-Sung
;
Chou, Yu-Szu
;
Wang, Guang-Ren
;
Chung, Wei-An
;
Wu, Pu-Wei
We demonstrate a composite approach to improve the mechanical strength of nanostructured Ni foams by producing a conformal coating of TiO2 on the skeletons of the Ni foam. The nanostructured Ni foam is fabricated by a template approach in which colloidal crystals of polystyrene microspheres in 720 nm diameter are constructed by a vertical electrophoresis process, followed by electroplating of Ni to fill the interstitial voids among the closely-packed microspheres and removal of the colloidal template afterward. The formation of TiO2 overcoat is achieved by optimization of sol-gel synthesis to prepare desirable TiO2 sols and their subsequent electrophoresis toward the nanostructured Ni foam in a square wave pulsing mode. The thickness of the TiO2 deposit is proportional to the duration of pulsing electrophoresis. From nano-indentation, the TiO2 -coated nanostructured Ni foams exhibit notable improvements in hardness (53-68%) and reduced elastic modulus (26-37%) over those of pristine nanostructured Ni foams. This strategy of implementing a thin ceramic overcoat provides an effective mean to improve the mechanical properties of nanostructured metals.
GaN vertical-cavity surface-emitting laser with a high-contrast grating reflector
(2018-01-01)
Chang, Tsu-Chi
;
Kuo, Shuo-Yi
;
Hashemi, Ehsan
;
Haglund, Asa
;
Lu, Tien-Chang
We report a GaN-based VCSEL with a high-contrast grating (HCG) as the top mirror. The HCG consisted of TiO2 and rested directly on the n-GaN without an airgap or the use of any DBR layers to boost the reflectivity. The full VCSEL structure was optically pumped at room temperature and showed a lasing threshold of approximately 0.69MW/cm(2) and a lasing wavelength at 369.1 nm. This first demonstration of lasing in a HCG GaN based VCSEL opens up the possibility to explore all the potential benefits of HCGs in the blue and ultraviolet spectral regime.
Lasing action in GaN-based VCSELs with top high-contrast grating reflectors
(2018-01-01)
Chang, Tsu-Chi
;
Kuo, Shuo-Yi
;
Hashemi, Ehsan
;
Haglund, Asa
;
Lu, Tien-Chang
We report a GaN-based VCSEL with a high-contrast grating (HCG) as the top mirror. The HCG consisted of TiO2 and rested directly on the n-GaN without an airgap or the use of any DBR layers to boost the reflectivity. The full VCSEL structure was optically pumped at room temperature and showed a lasing threshold of approximately 0.99 MW/cm(2) and a lasing wavelength at 369.8 nm. The demonstration of HCG GaN-based VCSEL opens up the possibility to explore all the potential benefits of HCGs in the blue and ultraviolet spectral regime.
Characteristic of an innovative TiO2/Fe-0 composite for treatment of azo dye
(2007-12-01)
Huang, Chihpin
;
Hsieh, Wen-Pin
;
Pan, Jill Ruhsing
;
Chang, Sue-Min
;
環境工程研究所
The major problem for Fe-0 application is the degradation of performance as time due to the formation of a surface oxide layer and that for TiO2, is the limit of the efficiency due to the recombination phenomenon. To overcome the problems as well as to improve the performance, our laboratory has been inventing a novel catalyst, which was developed by coating synthesized sol-gel-derived TiO2 nanoparticles onto the surface of Fe-0. This composite was employed on the degradation of azo dye (Acid Black-24) in the aqueous solution. Results from XPS, XRD and FE-SEM analysis indicated that the laboratory-prepared nanoscale TiO2/Fe-0 material is a composite of TiO2 and Fe-0. The nanoscale TiO2/Fe-0 composite with UV irradiation can efficiently decolour and reduce TOC from the simulated wastewater containing Acid Black-24. The efficiency of the TiO2/Fe-0 composite with UV irradiation on AB-24 reduction is much more efficient than microscale, and nanoscale Fe-0 and TiO2 particle (P-25). The evidence shows that TiO2 particles by sol-gel process were coated on the Fe-0 particles surface, which is attributed to the longer life cycle of Fe-0 reactivity. (c) 2007 Elsevier B.V. All rights reserved.
High-Density and Low-Leakage-Current MIM Capacitor Using Stacked TiO2/ZrO2 Insulators
(2009-07-01)
Lin, S. H.
;
Chiang, K. C.
;
Chin, Albert
;
Yeh, F. S.
;
電子工程學系及電子研究所
We have fabricated high-kappa Ni/TiO2/ZrO2/TiN metal-insulator-metal (MIM) capacitors. A low leakage current of 8 x 10(-8) A/cm(2) at 125 degrees C was obtained with a high 38-fF/mu m(2) capacitance density and better than the ZrO2 MIM capacitors. The excellent device performance is due to the lower electric field in 9.5-nm-thick TiO2/ZrO2 devices to decrease the leakage current and to a higher kappa value of 58 for TiO2 as compared with that of ZrO2 to preserve the high capacitance density.
CMOS Fully Compatible Embedded Non-Volatile Memory System With TiO2-SiO2 Hybrid Resistive-Switching Material
(2011-03-01)
Lee, Ming-Daou
;
Ho, ChiaHua
;
Yao, Yeong-Der
;
材料科學與工程學系
;
Department of Materials Science and Engineering
We demonstrate a non-volatile CMOS fully compatible embedded memory cell with a hybrid resistive switching material, TiO2-SiO2, in a 0.18 mu m node CMOS process. Both voltage-and temperature-dependent transports indicate that a Schottky-type resistance switching model dominates the TiO2 based transition-metal-oxide resistive random access memory (TMO-RRAM) system. Data retention is improved by inserting a very thin SiO2 layer between the bottom electrode and TiO2 film to enhance the Schottky barrier height, while maintaining TiO2 based RRAM characteristics.
Computational Study on the Reactions of H2O2 on TiO2 Anatase (101) and Rutile (110) Surfaces
(2011-04-30)
Huang, Wen-Fei
;
Raghunath, P.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
This study investigates the adsorption and reactions of H2O2 on TiO2 anatase (101) and rutile (110) surfaces by first-principles calculations based on the density functional theory in conjunction with the projected augmented wave approach, using PW91, PBE, and revPBE functionals. Adsorption mechanisms of H2O2 and its fragments on both surfaces are analyzed. It is found that H2O2, H2O, and HO preferentially adsorb at the Ti-5c site, meanwhile HOO, O, and H preferentially adsorb at the (O-2c)(Ti-5c), (Ti-5c)(2), and O-2c sites, respectively. Potential energy profiles of the adsorption processes on both surfaces have been constructed using the nudged elastic band method. The two restructured surfaces, the 1/3 ML oxygen covered TiO2 and the hydroxylated TiO2, are produced with the H2O2 dehydration and deoxidation, respectively. The formation of main products, H2O(g) and the 1/3 ML oxygen covered TiO2 surface, is exothermic by 2.8 and 5.0 kcal/mol, requiring energy barriers of 0.8 and 1.1 kcal/mol on the rutile (110) and anatase (101) surface, respectively. The rate constants for the H2O2 dehydration processes have been predicted to be 6.65 x 10(-27) T-4.38 exp(-0.14 kcal mol(-1)/RT) and 3.18 x 10(-23) T-5.60 exp(-2.92 kcal mol(-1)/RT) respectively, in units of cm(3) molecule(-1) s(-1). (C) 2010 Wiley Periodicals, Inc. J Comput Chem 32: 1065-1081, 2011

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