Browsing by Author "Chen, Hsuan-An"

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Forming-free, bi-directional polarity conductive-bridge memory devices with Ge2Sb2Te5 solid-state electrolyte and Ag active electrode
(2015-01-07)
Huang, Yin-Hsien
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Chen, Hsuan-An
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Wu, Hsin-Han
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Hsieh, Tsung-Eong
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材料科學與工程學系
Preparation and characteristics of conductive-bridge random access memory devices containing Ge2Sb2Te5 (GST) chalcogenide as the solid-state electrolyte, Ag as the active electrode, and W-Ti as the counter electrode are presented. As revealed by the electrical measurement, only the samples containing crystalline GST exhibited the resistive switching behaviors. With an insertion of ZnS-SiO2 dielectric layer at the Ag/GST interface and a postannealing at 100 degrees C for 1 min, the sample exhibited the best electrical performance with satisfactory cycleability and retention properties. Moreover, the forming-free and bi-directional polarity features were observed in such a sample type. Microstructure and composition analyses found the finely dispersed nano-scale Ag clusters in GST and, when electrical bias is applied, the migrating Ag ions may build up the connections in between neighboring Ag clusters. Moreover, grain boundaries in polycrystalline GST might be the main paths for Ag migration. The thread-like conduction channels in GST hence form, leading to the low resistance state of sample. On the contrary, the depletion of Ag in GST broke the connections in between Ag clusters when the electrical bias is reversed. This led to the rupture of conduction channels and, hence, the high resistance state of sample. The low operational voltage, forming-free, and bi-directional polarity features observed in (AZGW)(T) sample might also originated from the fine dispersion of Ag clusters in GST electrolyte. (C) 2015 AIP Publishing LLC.
GaSb/GaAs quantum dots and rings grown under periodical growth mode by using molecular beam epitaxy
(2015-09-01)
Chen, Hsuan-An
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Shih, Tung-Chuan
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Tang, Shiang-Feng
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Weng, Ping-Kuo
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Gau, Yau-Tang
GaSb/GaAs quantum dots (QDs) and quantum rings (QRs) are investigated. By using periodical growth interrupts, precise coverage control can be achieved for GaSb QD growth by using a single Ga source. With direct As irradiation to the substrate surface during the post soaking time, the soaking time can be effectively reduced while full ring morphologies and room-temperature QR luminescence can still be obtained by using this method. (C) 2015 Elsevier B.V. All rights reserved.
Long-Wavelength In-Plane Gate InAs Quantum-Dot Phototransistors
(2015-02-01)
Chen, Hsuan-An
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Shih, Tung-Chuan
;
Lin, Shih-Yen
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光電工程學系
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Department of Photonics
In-plane gate transistors with and without an InAs quantum-dot (QD) absorption layer are investigated. The n-GaAs channel acts as both an absorption layer for incident light with energy higher than the GaAs bandgap and the transport path for the photocurrents. The insertion of InAs QD layer not only extends the absorption wavelength to 1.26 mu m, but also enhances the optical response from GaAs.
Multiple-Layered Type-II GaSb/GaAs Quantum Ring Solar Cells Under Concentrated Solar Illumination
(2016-01-01)
Jheng, Yun-Han
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Hsu, Shun-Chieh
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Wu, Shou-Hung
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Sheu, Jinn-Kong
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Lo, Yuan-Ting
A multiple-layered type-II quantum ring nanostructure was embedded in the regular GaAs single junction solar cell to extend its infrared response. Three different designs were implemented and the location of quantum ring layers was investigated. Under one Sun condition, the n-type quantum ring device showed higher J(sc) than the GaAs reference while the reduction of V-oc is minimum among all these quantum ring samples. Further tests through the filtered infrared light demonstrate the enhanced photo-currents from quantum ring devices. An increase as high as 292% in reverse-biased photo-current can be observed.
Positioning Effect of Type-II GaSb/GaAs Quantum Ring Layer on Solar Cell Performances
(2015)
Hsu, Shun-Chieh
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Chen, Yin-Han
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Chen, Hsuan-An
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Lin, Shih-Yen
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Shen, Tien-Lin
In this work, we demonstrate the positioning effect of the type-II quantum ring (QR) on the solar cell efficiencies. The QR layer was placed in either p-type or n-type region to test its effect on the performance. Under one Sun condition, the one with p-type QR layer has better efficiency and open-circuit voltage. But this advantage loses quickly when the sunlight is concentrated over 20 times. From the concentrated sunlight measurement, the sample with QR layer in the n-type region can sustain the V-oc reduction until 80 Suns.
Scalable MoS2/graphene hetero-structures grown epitaxially on sapphire substrates for phototransistor applications
(2018-02-01)
Chen, Hsuan-An
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Chen, Wei-Chan
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Sun, Hsu
;
Lin, Chien-Chung
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Lin, Shih-Yen
Bi-layer graphene is grown directly on sapphire substrates by using ethane as the precursor without the assistance of a metal catalyst. A growth model of graphene flake formation in the furnace, followed by a complete film growth is also proposed. Using the graphene/sapphire sample as the new substrate, scalable MoS2 films with good layer number controllability can be grown directly on the substrate. After fabricating the MoS2/graphene hetero-structures into bottom-gate photo-transistors, a Dirac point shift is observed for the device under the light irradiation condition, which is attributed to the extraction of photo-excited electrons in the MoS2 layer to the graphene channel. The photo-voltaic response observed for the photo-transistors may provide a potential application of the 2D material hetero-structure in thin-film solar cells.
Single-Crystal Antimonene Films Prepared by Molecular Beam Epitaxy: Selective Growth and Contact Resistance Reduction of the 2D Material Heterostructure
(2018-05-02)
Chen, Hsuan-An
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Sun, Hsu
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Wu, Chong-Rong
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Wang, Yu-Xuan
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Lee, Po-Hsiang
Single-crystal antimonene flakes are observed on sapphire substrates after the postgrowth annealing procedure of amorphous antimony (Sb) droplets prepared by using molecular beam epitaxy at room temperature. The large wetting angles of the antimonene flakes to the sapphire substrate suggest that an alternate substrate should be adopted to obtain a continuous antimonene film. By using a bilayer MoS2/sapphire sample as the new substrate, a continuous and single-crystal antimonene film is obtained at a low growth temperature of 200 degrees C. The results are consistent with the theoretical prediction of the lower interface energy between antimonene and MoS2. The different interface energies of antimonene between sapphire and MoS2 surfaces lead to the selective growth of antimonene only atop MoS2 surfaces on a prepatterned MoS2/sapphire substrate. With similar sheet resistance to graphene, it is possible to use antimonene as the contact metal of 2D material devices. Compared with Au/Ti electrodes, a specific contact resistance reduction up to 3 orders of magnitude is observed by using the multilayer antimonene as the contact metal to MoS2. The lower contact resistance, the lower growth temperature, and the preferential growth to other 2D materials have made antimonene a promising candidate as the contact metal for 2D material devices.
Speckle reduction using deformable mirrors with diffusers in a laser pico-projector
(2017-07-24)
Chen, Hsuan-An
;
Pan, Jui-Wen
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Yang, Zu-Po
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光電系統研究所
;
影像與生醫光電研究所
We propose a design for speckle reduction in a laser pico-projector adopting diffusers and deformable mirrors. This research focuses on speckle noise suppression by changing the angle of divergence of the diffuser. Moreover, the speckle contrast value can be further reduced by the addition of a deformable mirror. The speckle reduction ability obtained using diffusers with different divergence angles is compared. Three types of diffuser designs are compared in the experiments. For Type 1 which uses a circular symmetric diffuser the speckle contrast value can be decreased to 0.0264. For Type 2, the speckle contrast value can be reduced to 0.0267 because of the inclusion of an elliptical distribution diffuser. With Type 3 which includes a combination of the circular distribution diffuser and elliptical distribution diffuser, the speckle contrast value can be reduced to 0.0236. For all three types, the speckle contrast value is lower than 0.05. Under this speckle value, the speckle phenomenon is invisible to the human eye. (C)2017 Optical Society of America
Type-II Superlattice Infrared Photodetectors With Graphene Transparent Electrodes
(2017-10-01)
Chen, Hsuan-An
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Chen, Hsuan-Yu
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Chen, Wei-Chan
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Lin, Shih-Yen
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影像與生醫光電研究所
In this letter, we have demonstrated that graphene can act as a transparent electrode on the p-type GaSb substrate. Wavelength-insensitive and over 95% high transmittance are observed for the bi-layer graphene in the infrared light range. By using graphene as the transparent electrode, over ten-time responsivity enhancement is observed for the InAs/GaSb type-II superlattice infrared photodetector. The phenomenon is attributed to the shortened carrier transport paths resulted from the vertical current flow to the graphene electrode. The results have revealed the potential of graphene for the application of infrared transparent electrodes.