Browsing by Author "Chang, Yuan-Ming"

Now showing 1 - 20 of 26

A Triode Device with a Gate Controllable Schottky Barrier: Germanium Nanowire Transistors and Their Applications
(1970-01-01)
Lin, Che-Yi
;
Chen, Chao-Fu
;
Chang, Yuan-Ming
;
Yang, Shih-Hsien
;
Lee, Ko-Chun
Electrical contacts often dominate charge transport properties at the nanoscale because of considerable differences in nanoelectronic device interfaces arising from unique geometric and electrostatic features. Transistors with a tunable Schottky barrier between the metal and semiconductor interface might simplify circuit design. Here, germanium nanowire (Ge NW) transistors with Cu3Ge as source/drain contacts formed by both buffered oxide etching treatments and rapid thermal annealing are reported. The transistors based on this Cu3Ge/Ge/Cu3Ge heterostructure show ambipolar transistor behavior with a large on/off current ratio of more than 10(5) and 10(3) for the hole and electron regimes at room temperature, respectively. Investigations of temperature-dependent transport properties and low-frequency current fluctuations reveal that the tunable effective Schottky barriers of the Ge NW transistors accounted for the ambipolar behaviors. It is further shown that this ambipolarity can be used to realize binary-signal and data-storage functions, which greatly simplify circuit design compared with conventional technologies.
Analog Circuit Applications Based on All-2D Ambipolar ReSe2 Field-Effect Transistors
(2019-05-01)
Lee, Ko-Chun
;
Yang, Shih-Hsien
;
Sung, Yung-Shang
;
Chang, Yuan-Ming
;
Lin, Che-Yi
Complementary circuits based on 2D materials show great promise for next-generation electronics. An ambipolar all-2D ReSe2 field-effect transistor (FET) with a hexagonal boron nitride gate dielectric is fabricated and its electronic characteristics are comprehensively studied by temperature dependence and noise measurements. Ambipolar transfer characteristics are achieved owing to the tunable Fermi level of the graphene contact and negligible and 30 meV Schottky barrier heights for the n- and p-channel regimes, respectively. An inverter is also fabricated to demonstrate ambipolar ReSe2 FET operation in a logic circuit. Furthermore, a p/n switchable unipolar FET is designed and shows potential for building complimentary circuits from a signal device. This work demonstrates the potential of all-2D ReSe2 FETs and makes available new approaches for designing next-generation devices.
Atomically thin van der Waals tunnel field-effect transistors and its potential for applications
(2019-03-08)
Yang, Shih-Hsien
;
Yao, You-Teng
;
Xu, Yong
;
Lin, Che-Yi
;
Chang, Yuan-Ming
Power dissipation is a crucial problem as the packing density of transistors increases in modern integrated circuits. Tunnel field-effect transistors (TFETs), which have high energy filtering provided by band-to-band tunneling (BTBT), have been proposed as an alternative electronics architecture to decrease the energy loss in bias operation and to achieve steep switching at room temperature. Very recently, the BTBT behavior has been demonstrated in van der Waals heterostructures by using unintentionally doped semiconductors. The reason of the BTBT formation is attributed to a significant band bending near the heterointerface, resulting in carrier accumulations. In this work, to investigate charge transport in type-III transistors, we adopted the same band-bending concept to fabricate van der Waals BP/MoS2 heterostructures. Through analyzing the temperature dependence of their electrical properties, we carefully ruled out the contribution of metal-semiconductor contact resistances and improved our understanding of carrier injection in 2D type-III transistors. The BP/MoS2 heterostructures showed both negative differential resistance and 1/f(2) current fluctuations, strongly demonstrating the BTBT operation. Finally, we also designed a TFET based on this heterostructure with an ionic liquid gate, and this TFET demonstrated an subthreshold slope can successfully surmount the thermal limit of 60 mV/decade. This work improves our understanding of charge transport in such layered heterostructures and helps to improve the energy efficiency of next-generation nanoscale electronics.
Broadband antireflection and field emission properties of TiN-coated Si-nanopillars
(2014-08-21)
Chang, Yuan-Ming
;
Ravipati, Srikanth
;
Kao, Pin-Hsu
;
Shieh, Jiann
;
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.
Broadband Omnidirectional Light Trapping in Gold-Decorated ZnO Nanopillar Arrays
(2017-04-05)
Chang, Yuan-Ming
;
Lin, Man-Ling
;
Lai, Tung-Yen
;
Chen, Chang-Hung
;
Lee, Hsin-Yi
The photoluminescence (PL) and reflectivity characteristics of zinc oxide nanopillars- (ZnO-NPs) grown on indium tin oxide (ITO)-coated glasses were investigated. The room temperature PL showed bright -white -light emission for the undoped ZnO-NPs grown at 600 degrees C, suggesting the close relation between the optical characteristic and "the growth conditions being, carried out for,obtaining the present ZnO-NPs. The reflectivity of the as -grown ZnO-NPs array was about, similar to 29% with the wavelength of the incident light ranging from 200 to 1800 nm. Nevertheless, the reflectance reduced significantly to less than 9.9% when a layer of gold (Au) was deposited on ZnO=NPg by sputtering for 5 min, corresponding to more than 65% reduction in Au -coated ZnQ-NPs (Au/ZnO-NPs). Moreover, the angle -resolved reflectance measurement's on the present Au/ZnO-NPs array show an omnidirectional light -trapping characteristic. These remarkable characteristics, broadband and omnidirectional light -trapping -of Ati/ZnO-NPs, are attributed to the extended effective optical path of the incident light due to subwavelength scattering resulting,from the presence of Au nanoparticics.
Effect of annealing temperature for Si0.8Ge0.2 epitaxial thin films
(2008-03-15)
Chang, Yuan-Ming
;
Dai, Ching-Liang
;
Cheng, Tsung-Chieh
;
Hsu, Che-Wei
;
機械工程學系
This study investigates the effect of annealing temperature on the Si0.8Ge0.2 epitaxial layers. The Si0.8Ge0.2 epitaxial layers were deposited by using ultrahigh vacuum chemical vapor deposition (UHVCVD) with different annealing temperatures ((400-1000 degrees C). Various measurement technologies, including high-resolution X-ray diffraction ((HRXRD), atomic force microscopy ((AFM) and interfacial adhesion tester, were used to characterize the materials properties of the SiGe epilayers. The experimental results showed that the SiGe epilayers gradually reduced lattice-mismatch to the underlying substrate as annealing temperature increased (from 400 to 800 degrees C), which resulted from a high temperature enhancing interdiffusion between the epilayers and the underlying substrate. In addition, the average grain size of the SiGe films increased from 53.3 to 58 nm with increasing annealing temperature. The surface roughness in thin film annealed at 800 degrees C was 0.46 nm. Moreover, the interfacial adhesion strength increased from 476 +/- 9 to 578 +/- 12 kg/cm(2) with increasing the annealing temperature. (c) 2007 Elsevier B.V. All rights reserved.
Enhanced field emission characteristics in metal-coated Si-nanocones
(2013)
Chang, Yuan-Ming
;
Kao, Pin-Hsu
;
Tai, Hung-Ming
;
Wang, Hau-Wei
;
Lin, Chih-Ming
Metallic gold (Au) and platinum (Pt) thin films were deposited on silicon nanocones (Si-NCs) by sputtering to elucidate the effects of work function and conductivities on the field electron emission characteristics of surface-modified Si-NCs. The results showed that for Pt/Si-NCs and Au/Si-NCs, although the turn-on field defined at a corresponding current density of 10 mu A cm(-2) only improved from 4.20 V mu m(-1) for bare Si-NCs to 3.65 and 2.90 V mu m(-1), respectively, the emission current density measured at 5.00 V mu m(-1) was enhanced by orders of magnitude, reaching 1.82 mA cm(-2) for Au/Si-NCs. Compared to those obtained from various surface-modified Si-nanostructures, such as ZnO/Si-nanopillars and ferroelectrics/Si-nanotips, the current results represent an interesting alternative route for producing surface-modified Si-NCs that might be useful for optical and electronic applications.
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
;
Shieh, Jiann
;
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.
Enhanced visible photoluminescence from ultrathin ZnO films grown on Si-nanowires by atomic layer deposition
(2010-09-24)
Chang, Yuan-Ming
;
Jian, Sheng-Rui
;
Lee, Hsin-Yi
;
Lin, Chih-Ming
;
Juang, Jenh-Yih
Bright room temperature visible emission is obtained in heterostructures consisting of similar to 3.5 nm thick ZnO ultrathin films grown on Si-nanowires produced by means of self-masking dry etching in hydrogen-containing plasma. The ZnO films were deposited on Si-nanowires by using atomic layer deposition (ALD) under an ambient temperature of 25 degrees C. The orders of magnitude enhancement in the intensity of the room temperature photoluminescence peaked around 560 nm in the present ZnO/Si-nanowire heterostructures is presumably due to the high aspect (surface/volume) ratio inherent to the Si-nanowires, which has, in turn, allowed considerably more ZnO material to be grown on the template and led to markedly more efficient visible emission. Moreover, the ordered nanowire structure also features an extremely low reflectance (similar to 0.15%) at 325 nm, which may further enhance the efficiency of emission by effectively trapping the excitation light.
Fabrication and optoelectronic properties of core-shell biomimetic ZnO/Si nanoball arrays
(2012)
Chang, Yuan-Ming
;
Kao, Pin-Hsu
;
Liu, Mao-Chen
;
Lin, Chih-Ming
;
Lee, Hsin-Yi
We report an effective process scheme comprising a single-step Ag sputtering with subsequent dry etching and atomic layer deposition (ALD) process for fabricating biomimetic ZnO/Si nanoball (ZnO/Si-NB) core-shell nanostructures directly on Si substrates. The obtained ZnO/Si-NB core-shell nanostructures consist of similar to 30 nm thick ZnO films grown on Si frustums produced by means of dry etching masked by the self-assembled silver nanodots created by single-step sputtering. The ZnO films were deposited using atomic layer deposition under an ambient temperature of 200 degrees C. The photoluminescence (PL) measurements on these ZnO/Si-NB core-shell nanostructures showed that the visible range emission was almost completely absent and only the ultraviolet emission (3.28 eV peak) resulting from the free excitons was observed, indicating that the films indeed have high crystalline quality. Moreover, a dramatic improvement of the field emission performance was observed for ZnO/Si-NB core-shell nanostructures as compared to the bare Si frustum arrays. The detailed analyses on the field enhancement factor (beta value) based on the Fowler-Nordheim field emission model indicate that the effective work function of the ZnO/Si-NB core-shell nanostructures might be significantly different from that of either ZnO or Si.
Field Emission in Vertically Aligned ZnO/Si-Nanopillars with Ultra Low Turn-On Field
(2012-03-01)
Chang, Yuan-Ming
;
Liu, Mao-Chen
;
Kao, Pin-Hsu
;
Lin, Chih-Ming
;
Lee, Hsin-Yi
An effective method of fabricating vertically aligned silicon nanopillars (Si-NPs) was realized by using the self-assembled silver (Ag) nanodots as natural metal-nanomask during dry etching process. The obtained Si-NPs were preferentially aligned along the c-axis direction. Ultrathin ZnO films (similar to 9 nm) were subsequently deposited on the Si-NPs by atomic layer deposition (ALD) to enhance the field emission property. The average diameter of the ZnO/Si-NPs is in the order of tens of nanometers, which enables efficient field emission and gives rise to marked improvement in the field enhancement factor, beta. The turn-on field defined by the 10 mu A/cm(2) current density criterion is similar to 0.74 V/mu m with an estimated beta approximate to 1.33x10(4). The low turn-on field and marked enhancement in beta were attributed to the small radius of curvature, high aspect ratio, and perhaps more importantly, proper density distribution of the ZnO/Si-NPs.
Field Emission Properties of Gold Nanoparticle-Decorated ZnO Nanopillars
(2012-12-01)
Chang, Yuan-Ming
;
Lin, Man-Ling
;
Lai, Tung-Yen
;
Lee, Hsin-Yi
;
Lin, Chih-Ming
The structural and optoelectronic properties of ZnO nanopillars (ZnO-NPs) grown on Si substrates by the vapor transport deposition method were investigated. In particular, by varying the deposition duration and hence the morphology of the vertically aligned ZnO-NPs, the resultant field emission characteristics were systematically compared. In addition to identifying the advantageous field emission properties exhibited in the pencil-like ZnO-NPs, we observed that by adhering Au nanoparticles on the surface of the ZnO-NPs the turn-on field and the maximum current density can be drastically improved from 3.15 V/mu m and 0.44 mA/cm(2) at 5 V/mu m for the best ZnO-NPs to 2.65 V/mu m and 2.11 mA/cm(2) at 5 V/mu m for Au/ZnO-NPs, respectively. The enhancement of field emission characteristics that resulted from Au-nanoparticle decoration is discussed on the basis of charge-transfer-induced band structure modifications.
High Mobilities in Layered InSe Transistors with Indium-Encapsulation-Induced Surface Charge Doping
(2018-11-02)
Li, Mengjiao
;
Lin, Che-Yi
;
Yang, Shih-Hsien
;
Chang, Yuan-Ming
;
Chang, Jen-Kuei
Tunability and stability in the electrical properties of 2D semiconductors pave the way for their practical applications in logic devices. A robust layered indium selenide (InSe) field-effect transistor (FET) with superior controlled stability is demonstrated by depositing an indium (In) doping layer. The optimized InSe FETs deliver an unprecedented high electron mobility up to 3700 cm(2) V-1 s(-1) at room temperature, which can be retained with 60% after 1 month. Further insight into the evolution of the position of the Fermi level and the microscopic device structure with different In thicknesses demonstrates an enhanced electron-doping behavior at the In/InSe interface. Furthermore, the contact resistance is also improved through the In insertion between InSe and Au electrodes, which coincides with the analysis of the low-frequency noise. The carrier fluctuation is attributed to the dominance of the phonon scattering events, which agrees with the observation of the temperature-dependent mobility. Finally, the flexible functionalities of the logic-circuit applications, for instance, inverter and not-and (NAND)/not-or (NOR) gates, are determined with these surface-doping InSe FETs, which establish a paradigm for 2D-based materials to overcome the bottleneck in the development of electronic devices.
High Performance Cu-doped SiO2 ReRAM by a Novel Chemical Soak Method
(2011-01-01)
Chin, Fun-Tat
;
Yang, Wen-Luh
;
Chao, Tien-Sheng
;
Chang, Yuan-Ming
;
Lin, Li-Min
In this paper, a novel chemical soak method is proposed to fabricate a Cu-doped SiO2 ReRAM device. This method can easily fabricate a lightly Cu-doped SiO2 film and effectively improve the reliability of the conventional Cu-doped SiO2 ReRAM device. A reproducible bipolar switching characteristic with set/reset voltage (ca. 2.5 V/ -0.7 V) is performed in this device and the electrical conduction in HRS and LRS are related to Poole-Frenkel and Ohmic conduction, respectively. Excellent performance in terms of high on/off ratio (similar to 10(6)), narrow range distribution of set and reset voltages, stable data retention, and up to 110 times switching cycles has been achieved by this novel chemical soak method for Cu-doped SiO2 ReRAM device.
Multifunctional full-visible-spectrum optoelectronics based on a van der Waals heterostructure
(2019-12-01)
Yang, Shih-Hsien
;
Lee, Ko-Chun
;
Tsai, Meng-Yu
;
Chang, Yuan-Ming
;
Lin, Che-Yi
Multifunctional devices are expected to allow development of low-cost, highly integrated, and energy-efficient electronics for the internet of things (IoT) era. Here, we demonstrate an all-two-dimensional ReSe2/h-BN/graphene heterostructure (ReSe2 HS) consisting of a vertically coupled ReSe2 field-effect transistor and charge storage component, which possesses multifunctional characteristics for use in electronics and optoelectronics. As an electrically controlled non-volatile memory (NVM), the ReSe2 HS delivers high-performance multilevel data storage with a readout on/off current ratio exceeding 10(5) and excellent durability (> 10(4) s) at an ultralow V-ds of 50 mV, which benefits to the development of power saving devices. The ReSe2 HS design and high-photoresponsivity ReSe2 channel also achieve an energy efficient optical NVM with full-visible-spectrum distinction. Besides, the ReSe2 HS displays unique ambipolarity to operate as either an inverter or frequency doubler. We further propose a power-free ReSe2 HS optical memory matrix to simplify imaging systems. The ReSe2 HS shows promise for use in light-programmable information storage systems and neuromorphic computation with low power consumption.
Nanocone SiGe antireflective thin films fabricated by ultrahigh-vacuum chemical vapor deposition with in situ annealing
(2010-05-03)
Chang, Yuan-Ming
;
Dai, Ching-Liang
;
Cheng, Tsung-Chieh
;
Hsu, Che-Wei
;
機械工程學系
In this study, we fabricated nanocone-presenting SiGe antireflection layers using only ultrahigh-vacuum chemical vapor deposition. In situ thermal annealing was adopted to cause SiGe clustering, yielding a characteristic nanocone array on the SiGe surface. Atomic force microscopy indicated that the SiGe nanocones had uniform height and distribution. Spectrophotometric measurements revealed that annealing at 900 degrees C yielded SiGe thin films possessing superior antireflective properties relative to those of the as-grown SiGe sample. We attribute this decrease in reflectance to the presence of the nanostructured cones. Prior to heat treatment, the mean reflectance of ultraviolet rays (wavelength <400 nm) of the SiGe thin film was ca. 61.7%; it reduced significantly to less than 28.5% when the SiGe thin film was annealed at 900 degrees C. Thus, the drop in reflectance of the SiGe thin film after thermal treatment exceeded 33%. (C) 2010 Elsevier B.V. All rights reserved.
Nanogrids and Beehive-Like Nanostructures Formed by Plasma Etching the Self-Organized SiGe Islands
(2010-09-01)
Chang, Yuan-Ming
;
Jian, Sheng-Rui
;
Juang, Jenh-Yih
;
電子物理學系
;
Department of Electrophysics
A lithography-free method for fabricating the nanogrids and quasi-beehive nanostructures on Si substrates is developed. It combines sequential treatments of thermal annealing with reactive ion etching (RIE) on SiGe thin films grown on (100)-Si substrates. The SiGe thin films deposited by ultrahigh vacuum chemical vapor deposition form self-assembled nanoislands via the strain-induced surface roughening (Asaro-Tiller-Grinfeld instability) during thermal annealing, which, in turn, serve as patterned sacrifice regions for subsequent RIE process carried out for fabricating nanogrids and beehive-like nanostructures on Si substrates. The scanning electron microscopy and atomic force microscopy observations confirmed that the resultant pattern of the obtained structures can be manipulated by tuning the treatment conditions, suggesting an interesting alternative route of producing self-organized nanostructures.
Negative-Differential-Resistance Devices Achieved by Band-Structure Engineering in Silicene under Periodic Potentials
(2018-10-18)
Chen, Chang-Hung
;
Li, Wen-Wu
;
Chang, Yuan-Ming
;
Lin, Che-Yi
;
Yang, Shih-Hsien
An important development in modern electronics is the realization of band-structure engineering for the design of novel materials and devices. One possible way to realize band-structure engineering is by addition of periodic potentials to two-dimensional (2D) materials, such as graphene, to form a superstructure, known as a "superlattice.' Unlike the band gap of graphene, the band gap of silicene can be tuned by an out-of-plane electric field owing to its unusual buckled structure. In this work, we use the designable band gap of silicene and the band structure of superlattices, together with the spin and valley degrees of freedom, to propose a design principle for optimizing the performance of spin-and valley-dependent negative-differential-resistance (NDR) devices using silicene superlattices. On the basis of the effective Hamiltonian formalism, we predict that the peak-to-valley current ratio could be larger than most recently reported results achieved by 2D materials, suggesting that the silicene superlattice is a good candidate for realizing NDR devices. The design principle proposed in this work could also be extended to other layered materials with tunable band gaps. This could pave the way for advanced material and device designs based on band-gap engineering of 2D materials.
Optoelectronic properties in vertically aligned ZnO/Si-nanopillars
(2012)
Lee, Hsin-Yi
;
Chang, Yuan-Ming
;
Tseng, Wen-Shou
;
Kao, Pin-Hsu
;
Wang, Hau-Wei
An effective method of fabricating vertically aligned silicon nanopillars (Si-NPs) was realized by using the self-assembled silver nanodots as natural metal-nanomask for subsequent etching process. Ultrathin (similar to 9 nm) ZnO films were deposited on the Si-NPs by atomic layer deposition to enhance the field emission property. The turn-on field defined by the 10 mu A/cm(2) current density criterion is similar to 0.74 V/mu m with an estimated beta similar to 1.33X10(4). The low turn-on field and marked enhancement in beta were attributed to the small radius of curvature, high aspect ratio, and perhaps more importantly, proper density distribution of the ZnO/Si-NPs. On the other hand, room-temperature ultraviolet (UV) luminescence was investigated for the atomic layer deposited ZnO films grown on Si nanowires 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 was observed with a nearly complete suppression of the defect-associated broad visible range emission peak.
Optoelectronic Properties of Density-Controlled ZnO Nanopillar Arrays
(2012-04-12)
Chang, Yuan-Ming
;
Huang, Jheng-Ming
;
Lin, Chih-Ming
;
Lee, Hsin-Yi
;
Chen, San-Yuan
An effective method of controlling the density of ZnO nanopillars (ZnO-NPs) by using the self-assembled silver nanoislands as the growth catalyst is demonstrated. We were able to vary the density of the ZnO-NPs to within the range of similar to 10-30 mu m(-2) by properly manipulating the size distribution of the silver nanoislands partially covering the Si substrates. Continuous silver film can also be used as the catalyst to facilitate the growth of ZnO islands and pillars on Si substrates, albeit with much less control of the resultant density and morphological appearances. The field emission measurements indicate that the performance of field emission for ZnO-NPs can be. improved markedly by reducing the density of the ZnO-NPs. The turn-on field of the low-density ZnO-NPs was as low as 2.39 V/mu m with a corresponding current density of 10 mu A/cm(2) and a field enhancement factor (beta value) of similar to 3500. The enhancement of field emission characteristics is attributed to the much reduced field screen effect by properly controlled density of the ZnO-NPs.