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Scattering Behavior of Waveguide Channels of a New Coupled Integrable Dispersionless System
Abbagari Souleymanou, **, Victor K. Kuetche, Thomas B. Bouetou, , Timoleon C. Kofane
Chin. Phys. Lett. 2011, 28 (12):
120501
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DOI: 10.1088/0256-307X/28/12/120501
Based upon the powerful Hirota method for unearthing soliton solutions to nonlinear partial differential evolution equations, we investigate the scattering properties of a new coupled integrable dispersionless system while surveying the interactions between its self-confined travelling wave solutions. As a result, we ascertain three types of scattering features depending strongly upon a characteristic parameter. Using such findings to depict soliton solutions with nonzero angular momenta, we derive an extended form of the dispersionless system, which is valuable for further physical applications.
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Hurst's Exponent Determination for Radial Distribution Functions of In, Sn and In-40 wt%Sn Melt
ZHOU Yong-Zhi, LI Mei, GENG Hao-Ran**, YANG Zhong-Xi, SUN Chun-Jing
Chin. Phys. Lett. 2011, 28 (12):
120505
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DOI: 10.1088/0256-307X/28/12/120505
Hurst's exponent of radial distribution functions (RDFs) within the short-range scope of In, Sn and In-40 wt%Sn melts are determined by the rescaled range analysis method. Hurst's exponents H are between 0.94 and 0.97, which display long−range dependence. Within short-range scope, the number of particles from a reference particle belongs to fractional Brownian motion. After RDF serials are randomly scrambled, Hurst's exponents all dramatically dropped, which proves long-range dependence. H irregularly varies as the temperature rises, but the change tendency is not consistent with the correlation radius rc.
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Fast Nondestructive Identification of Endothelium Corneum Gigeriae Galli Using Visible/Near-Infrared Spectroscopy
ZHANG Xiao-Yan, MENG Yao-Yong, **, ZHANG Hao, OU Wen-Juan, LIU Song-Hao
Chin. Phys. Lett. 2011, 28 (12):
120701
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DOI: 10.1088/0256-307X/28/12/120701
Vis/NIR spectroscopy, in combination with partial least square (PLS) analysis and a back-propagation neural network, is investigated to identify endothelium corneum gigeriae galli (ECGG). The spectral features of ECGGs and their counterfeits are reasonably differentiated in vis/NIR region, which provides enough qualitative information to establish the relationship between the spectra and samples for identification. After pretreatment of the spectral data, cross validation is implemented for extracting the best number of principal components. Then the calibration and validation set are performed well. The PLS and back propagation neural network (BPNN) model gives the BPNN to be 0.9941 and the root mean square residual (RMSR) to be 0.0775 for the calibration set, and the multiple correlation coefficient (MCC) to 0.9874 and the RMSE to 0.1134 for the validation set. Thus the PLS and BPNN model is reliable and practicable. Through testing, a recognition accuracy of 100% is achieved. The present study could offer a new approach for fast and nondestructive discrimination of ECGG and its counterfeit.
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Elastic Scattering Properties of Ultracold Strontium Atoms
ZHANG Ji-Cai**, ZHU Zun-Lue, LIU Yu-Fang, SUN Jin-Feng,
Chin. Phys. Lett. 2011, 28 (12):
123401
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DOI: 10.1088/0256-307X/28/12/123401
We investigate the elastic scattering properties of strontium atoms at ultracold temperatures. The scattering parameters, such as s-wave scattering lengths, effective ranges and p-wave scattering lengths, are calculated for all stable isotope combinations of Sr atoms by the quantal method and semiclassical method, respectively. Good agreements are obtained. The scattering parameters are very sensitive to small changes of the reduced mass. Due to the repulsive interisotope and intraisotope s-wave scattering length and large elastic cross sections, 84Sr–86Sr mixture is a good candidate to realize Bose–Bose quantum degenerate atomic gases.
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Transmission Characteristics of a Generalized Parallel Plate Dielectric Waveguide at THz Frequencies
YE Long-Fang, **, XU Rui-Min, ZHANG Yong, LIN Wei-Gan
Chin. Phys. Lett. 2011, 28 (12):
124102
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DOI: 10.1088/0256-307X/28/12/124102
A generalized parallel-plate dielectric waveguide (G-PPDW) is proposed as a new guiding medium for terahertz wave. A theoretical analysis of the transmission characteristics for the TE modes of this generalized structure is performed. Equations are presented for the field components, dispersion, power ratio, transmission loss and characteristic impedance as functions of the operating frequencies, dimensions and material constants. In the case of the lowest-order mode TE10, design curves covering frequencies and dimensions for the given material constants in the THz region are presented. The theoretical results of transmission characteristics obtained from these equations are verified by the finite-element method with a good agreement. The investigation results show that by selecting proper dimensions and dielectric materials, G-PPDW can be used to guide THz waves efficiently with high power confinement and low attenuation. These outstanding properties may open up a way to many important applications for THz integrated circuits and systems.
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Ghost Imaging Using Orbital Angular Momentum
ZHAO Sheng-Mei**, DING Jian, DONG Xiao-Liang, ZHENG Bao-Yu
Chin. Phys. Lett. 2011, 28 (12):
124207
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DOI: 10.1088/0256-307X/28/12/124207
We present a novel encoding scheme in a ghost-imaging system using orbital angular momentum. In the signal arm, object spatial information is encoded as a phase matrix. For an N−grey-scale object, different phase matrices, varying from 0 to π with increment π/N, are used for different greyscales, and then they are modulated to a signal beam by a spatial light modulator. According to the conservation of the orbital angular momentum in the ghost imaging system, these changes will give different coincidence rates in measurement, and hence the object information can be extracted in the idler arm. By simulations and experiments, the results show that our scheme can improve the resolution of the image effectively. Compared with another encoding method using orbital angular momentum, our scheme has a better performance for both characters and the image object.
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Methods of Generation and Detailed Characterization of Millimeter-Scale Plasmas Using a Gasbag Target
LI Zhi-Chao, **, ZHENG Jian, JIANG Xiao-Hua, WANG Zhe-Bin, YANG Dong, ZHANG Huan, LI San-Wei, WANG Feng, PENG Xiao-Shi, YIN Qiang, ZHU Fang-Hua, GUO Liang, YUAN Peng, LIU Shen-Ye, DING Yong-Kun
Chin. Phys. Lett. 2011, 28 (12):
125202
.
DOI: 10.1088/0256-307X/28/12/125202
Gasbag targets are useful for the research of laser-plasma interactions in inertial confinement fusion, especially in the laser overlapping regime. We report that on the Shengguang-II laser facility, millimeter−scale plasmas are successfully generated by four 0.35 µm laser beams using a gasbag target. Multiple diagnostics are applied to characterize the millimeter−scale plasmas in detail. The images from the x-ray pinhole cameras confirm that millimeter-scale plasmas are indeed created. An optical Thomson scattering system diagnoses the electron temperature of the CH filling plasmas by probing the thermal ion-acoustic fluctuations, which indicates that the electron temperature has a 600 eV flat roof in 0.7–1.3 ns. Another key parameter, i.e. the electron density of the millimeter-scale plasmas, is inferred by the spectrum of the back stimulated Raman scattering of an additional 0.53 µm laser beam. The inferred electron density keeps stable at 0.1nc in early time consistent with the controlled filling pressure and splits into a higher density in late time, which is attributed to the blast wave entering into the SRS interaction region.
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Structural and Electronic Properties, and Pressure-Induced Phase Transition of Layered C5N: a First-Principles Investigation
HU Qian-Ku, **, WANG Hai-Yan, WU Qing-Hua, HE Ju-Long, ZHANG Guang-Lei
Chin. Phys. Lett. 2011, 28 (12):
126101
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DOI: 10.1088/0256-307X/28/12/126101
Seven layered C5N configurations constructed from hexagonal BN and graphite structures are studied using an ab initio pseudopotential density functional method. The structural and electronic properties, and pressure−induced phase transition are investigated by calculating the total energy, structural parameter, formation energy, elastic constant, band structure and electron density of state. The results show that the three C5N configurations constructed from the h−BN structure are more stable energetically than those four configurations from graphite structure. The C5N−I configuration with the highest symmetry and the AA stacking sequence along the c−axis is the most stable. This structure is stable mechanically and its phase separation is difficult. The C5N phase is expected to have a metallic character. A critical pressure of about 20 GPa is predicted for the synthesis of a monoclinic C5N phase from the layered C5N phase.
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First-Principles Study of Fe-Doped ZnO Nanowires
ZHANG Fu-Chun**, ZHANG Wei-Hu, DONG Jun-Tang, ZHANG Zhi-Yong
Chin. Phys. Lett. 2011, 28 (12):
126102
.
DOI: 10.1088/0256-307X/28/12/126102
Using first-principles theory, we predict magnetic, electronic and optical properties in Fe-doped ZnO nanowires. The results show that ferromagnetic (FM) coupling of configuration V is the most stable, and the strong hybridization effect between Fe 3d and O 2p states is found near the Fermi level, and it is obvious that the ferromagnetic system is electron−spin polarization of 100% and half-metallic. Given antiferromagnetic (AFM) coupling, the system generates small spin polarization near the Fermi level, indicating metallicity. The magnetic moments mainly arise from Fe 3d orbitals. In addition, the results of optical properties show that the Fe-doped ZnO nanowires have apparent absorption peaks in the ultraviolet band and that there is a small red shift and a strong blue shift in the near and far ultraviolet band, indicating that Fe-doped ZnO nanowires are a type of magneto-optical materials with great promise.
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In situ High-Pressure Synchrotron X-Ray Diffraction Study of Clinozoisite
FAN Da-Wei**, MA Mai-Ning, YANG Jun-Jie, WEI Shu-Yi, CHEN Zhi-Qiang, XIE Hong-Sen
Chin. Phys. Lett. 2011, 28 (12):
126103
.
DOI: 10.1088/0256-307X/28/12/126103
We investigate the elastic behavior of a natural clinozoisite under about 20.4 GPa at 300 K using in situ angle-dispersive x-ray diffraction and a diamond anvil cell at the National Synchrotron Light Source, Brookhaven National Laboratory. Over this pressure range, no phase change or disproportionation has been observed. The isothermal equation of state is determined. The values of V0 and K0 refined by the Murnaghan equation of state are V0=460.0±0.2 Å3, K0=138±3 GPa. Consequently, it can be concluded that the compressibility of clinozoisite under high pressures is accurately constrained.
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Production and Mechanical Behaviour of Biomedical CoCrMo Alloy
O. Sahin**, A. R, za Tuncdemir, H. Ali Cetinkara, H. Salih Guder, E. Sahin
Chin. Phys. Lett. 2011, 28 (12):
126201
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DOI: 10.1088/0256-307X/28/12/126201
Cobalt-based alloy (Co-30Cr-5.5Mo) is produced by the investment casting process. This alloy complies with the ASTM F75 standard and is widely used in the manufacturing of orthopedic implants because of its high strength, good corrosion resistance and excellent biocompatibility properties. SEM, XRD and microhardness tests are used to examine the mechanical properties of the material. The examined material exhibits the behaviour of indentation size effect (ISE). Our results reveal that Vickers and Knoop microhardness are dependent on indentation test load. The traditional Meyer's law, the proportional specimen resistance (PSR) model and the Hays-Kendall model (HK) are used to analyze the load dependence of the hardness. As a result, the Hays-Kendall model is found to be the most effective to determine the load-independent hardness HLI of CoCrMo alloy.
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Magnetism of a Nitrogen-Implanted TiO2 Single Crystal
LIU Chun-Ming**, XIANG Xia, ZHANG Yan, JIANG Yong, ZU Xiao-Tao
Chin. Phys. Lett. 2011, 28 (12):
127201
.
DOI: 10.1088/0256-307X/28/12/127201
Single rutile crystal TiO2 was implanted using nitrogen ions with energy of 60 keV. The microstructure, ultraviolet−visible light absorption spectra, conductivity and magnetism are investigated. Except for the nitrogen dopant, no impurity can be detected by x-ray diffraction and x-ray photoelectron spectra. The absorption in the visible light region is enhanced with nitrogen implantation dose increasing. By measuring the temperature dependence of resistance, it is found that the sample implanted with 1×1018 ions/cm2 is changes from insulating to semiconducting, and the variable range hopping is the main conducting mechanism. Room-temperature ferromagnetism is also obtained in this sample. The magnetism as a function of temperature can be well fitted using the three-dimensional spin wave model plus the Curie–Weiss model, indicating that there is a mixed phase of ferromagnetism and paramagnetism.
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Wafer-Scale Gigahertz Graphene Field Effect Transistors on SiC Substrates
PAN Hong-Liang, JIN Zhi**, MA Peng, GUO Jian-Nan, LIU Xin-Yu, YE Tian-Chun, LI Jia, DUN Shao-Bo, FENG Zhi-Hong
Chin. Phys. Lett. 2011, 28 (12):
127202
.
DOI: 10.1088/0256-307X/28/12/127202
Wafer-scale graphene field-effect transistors are fabricated using benzocyclobutene and atomic layer deposition Al2O3 as the top−gate dielectric. The epitaxial-graphene layer is formed by graphitization of a 2-inch-diameter Si-face semi-insulating 6H-SiC substrate. The graphene on the silicon carbide substrate is heavily n-doped and current saturation is not found. For the intrinsic characteristic of this particular channel material, the devices cannot be switched off. The cut-off frequencies of these graphene field-effect transistors, which have a gate length of 1 µm , are larger than 800 MHz. The largest one can reach 1.24 GHz. There are greater than 95% active devices that can be successfully applied. We thus succeed in fabricating wafer-scale gigahertz graphene field-effect transistors, which paves the way for high-performance graphene devices and circuits.
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Improved Performance of Pentacene Organic Field-Effect Transistors by Inserting a V2O5 Metal Oxide Layer
ZHAO Geng, CHENG Xiao-Man, **, TIAN Hai-Jun, DU Bo-Qun, LIANG Xiao-Yu
Chin. Phys. Lett. 2011, 28 (12):
127203
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DOI: 10.1088/0256-307X/28/12/127203
We fabricate pentacene-based organic field effect transistors (OFETs), inserting a transition metal oxide (V2O5) layer between the pentacene and Al source−drain (S/D) electrodes. The performance of the devices with V2O5/Al S/D electrodes is considerably improved compared to the pentacene−based OFET with only Al S/D electrodes. After the 10-nm V2O5 layer modification, the effective field-effect mobility of the devices increases from 2.7×10−3 cm2/V⋅s to 8.93×10−1 cm2/V⋅s. Owing to the change of the injection property, the effective threshold voltage (Vth) is changed from −7.5 V to −5 V and the on/off ratio shifts from 102 to 104. Moreover, the dispersion of sub−threshold current in the devices disappears. These performance improvements are ascribed to the low carrier injection barrier and the reduction of contact resistance. It is indicated that V2O5 layer modification is an effective approach to improve pentacene-based OFET performance.
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The Evidence for Ferroelectricity on Magnetite Ceramics below the Verwey Transition
WU Yu-Qiang, WU Hong-Ying**, ZHAO Jie, LU Cui-Min, ZHANG Bao-Long, LIU Qing-Suo, MA Yong-Chang,
Chin. Phys. Lett. 2011, 28 (12):
127701
.
DOI: 10.1088/0256-307X/28/12/127701
We report the temperature- and frequency-dependent dielectric spectrum of magnetite ceramic single phase samples at 77.4–300 K and 200 Hz–1 MHz. In temperature-dependent dc resistivity, the sharp transition expected in single crystals is much suppressed. At higher temperatures, the grain boundaries contribute to the relaxation process. Below 120 K, the temperature-dependent dielectric constant reveals a weak broadened peak as cooling, from our analysis this behavior may be intrinsically correlated with the charge ordering of Fe3+ and Fe2+. Under a relatively low dc bias at 77.4 K, the polarization of the magnetite ceramic decreases, while under a much stronger electrical field, the dielectric spectrum in the lower frequency region is suppressed remarkably for the excitation of carriers bounded by grain boundaries.
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Enhancement of Er3+ Emission from an Er−Si Codoped Al2O3 Film by Stacking Si−Doped Al2O3 Sublayers
WANG Xiao, JIANG Zui-Min, XU Fei, **, MA Zhong-Quan, XU Run, YU Bin, LI Ming-Zhu, ZHENG Ling-Ling, FAN Yong-Liang, HUANG Jian, LU Fang
Chin. Phys. Lett. 2011, 28 (12):
127802
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DOI: 10.1088/0256-307X/28/12/127802
A multilayer film (multi-film), consisting of alternate Er-Si-codoped Al2O3 (ESA) and Si−doped Al2O3 (SA) sublayers, is synthesized by co−sputtering from separated Er, Si, and Al2O3 targets. The dependence of Er3+ related photoluminescence (PL) properties on annealing temperatures over 700–1100°C is studied. The maximum intensity of Er3+ photoluminance (PL), about 10 times higher than that of the monolayer film, is obtained from the multi−film annealed at 950°C. The enhancement of Er3+ PL intensity is attributed to the energy transfer from the silicon nanocrystals (Si−NCs) to the neighboring Er3+ ions. The effective characteristic interaction distance (or the critical ET length) between Er and carriers (Si−NCs) is ∼3 nm. The PL intensity exhibits a nonmonotonic temperature dependence. Meanwhile, the PL integrated intensity at room temperature is about 30% higher than that at 14 K.
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Density Increase of Upper Quantum Dots in Dual InGaN Quantum-Dot Layers
LV Wen-Bin, WANG Lai**, WANG Jia-Xing, HAO Zhi-Biao, LUO Yi
Chin. Phys. Lett. 2011, 28 (12):
128101
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DOI: 10.1088/0256-307X/28/12/128101
Single and dual layers of InGaN quantum dots (QDs) are grown by metal organic chemical vapor deposition. In the former, the density, average height and diameter of QDs are 1.3×109 cm−2, 0.93 nm and 65.1 nm, respectively. The latter is grown under the same conditions and possesses a 20 nm low-temperature grown GaN barrier between two layers. The density, average height and diameter of QDs in the upper layer are 2.6×1010 cm−2, 4.6 nm and 81.3 nm, respectively. Two reasons are proposed to explain the QD density increase in the upper layer. First, the strain accumulation in the upper layer is higher, leading to a stronger three-dimensional growth. Second, the GaN barrier beneath the upper layer is so rough it induces growth QDs.
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Herding Effect in Coupled Pedestrian-Pedestrian Interacting Dynamics
DING Jian-Xun**, LING Xiang, HUANG Hai-Jun, TAKASHI Imamura
Chin. Phys. Lett. 2011, 28 (12):
128301
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DOI: 10.1088/0256-307X/28/12/128301
A simple particle hopping model is proposed to investigate the interaction of two groups of pedestrians, namely straight walking pedestrians and cross-pedestrians. In the model, the straight walking pedestrians have greater priority walking on a main road, while other pedestrians arrive at the roadside and check to cross. Herding behavior, by which cross-pedestrians communicate with each other and self-organize to compete for common space with their straight walking counterparts, are newly introduced to reflect realistic crossing behavior in a crowed street. The results demonstrate that herding behavior brings adverse consequences to both types of pedestrians as a whole, although the pedestrians adopting prompt herding behavior can benefit. Furthermore, an increased number of crossing points to avoid the inefficiency of the coupled system is also investigated.
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Highly Efficient PCDTBT:PC71 BM Based Photovoltaic Devices without Thermal Annealing Treatment
YANG Shao-Peng**, KONG Wei-Guang, LIU Bo-Ya, ZHENG Wen-Yao, LI Bao-Min, LIU Xian-Hao, FU Guang-Sheng
Chin. Phys. Lett. 2011, 28 (12):
128401
.
DOI: 10.1088/0256-307X/28/12/128401
We propose an effective method to fabricate highly efficient organic photovoltaic cells based on poly [N−9"-hepta-decanyl-2, 7-carbazole-alt-5,5-(4'7'-di-2-thienyl-2'1'3'-b-enzothiadiazole):[6,6]-phenyl C71−butyric acid methyl ester (PCDTBT:PC71BM). A power conversion efficiency of as high as 5.6% and a fill factor of 53.7% are achieved from the optimized cells. The influence of surface morphology of the active layer on the performance of the cells is also investigated.
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Comparison of GaN-Based Light-Emitting Diodes by Using the AlGaN Electron-Blocking Layer and InAlN Electron-Blocking Layer
CHEN Jun, FAN Guang-Han**, PANG-Wei, ZHENG Shu-Wen
Chin. Phys. Lett. 2011, 28 (12):
128501
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DOI: 10.1088/0256-307X/28/12/128501
Optical properties of GaN-based light-emitting diodes (LEDs) are studied numerically by using AlGaN and InAlN electron-blocking layers (EBLs). Through the simulations of emission spectra, carrier concentration distribution, energy band, electrostatic field, internal quantum efficiency and output power, the results show that the LEDs with design of the InAlN EBL structure have a better performance over the original LEDs using an AlGaN EBL. The spectrum intensity and output power are enhanced significantly, and the efficiency droop of internal quantum efficiency is improved effectively with this design of InAlN EBL structure. It is proved that the strengths of carrier confinement and electron leakage current play a critical role in the performance of luminescence in LEDs.
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Characteristics and Time-Dependent Instability of Ga-Doped ZnO Thin Film Transistor Fabricated by Radio Frequency Magnetron Sputtering
HUANG Hai-Qin, SUN Jian, LIU Feng-Juan, ZHAO Jian-Wei, HU Zuo-Fu, LI Zhen-Jun, ZHANG Xi-Qing**, WANG Yong-Sheng
Chin. Phys. Lett. 2011, 28 (12):
128502
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DOI: 10.1088/0256-307X/28/12/128502
We report on the fabrication and electrical characteristics of Ga-doped ZnO thin film transistors (TFTs). Low Ga-doped (0.7wt%) ZnO thin films were deposited on SiO2/p−Si substrates by rf magnetron sputtering. The GZO TFTs show a mobility of 1.76 cm2/V⋅s, an on/off ratio of 1.0×106, and a threshold voltage of 35 V. The time−dependent instability of the TFT is studied. The VTH shifts negatively. In addition, the device shows a decrease of the on/off ratio, mainly due to the increase of the off-current. The mechanisms of instability are discussed.
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Design of a 1200-V Thin-Silicon-Layer p-Channel SOI LDMOS Device
HU Sheng-Dong, **, ZHANG Ling, LUO Xiao-Rong, ZHANG Bo, LI Zhao-Ji, WU Li-Juan
Chin. Phys. Lett. 2011, 28 (12):
128503
.
DOI: 10.1088/0256-307X/28/12/128503
A 1200-V thin-silicon-layer p-channel silicon-on-insulator (SOI) lateral double-diffused metal-oxide-semiconductor (LDMOS) transistor is designed. The device named INI SOI p-LDMOS is characterized by a series of equidistant high concentration n+ islands inserted at the interface of a top silicon layer and a buried oxide layer. Accumulation−mode holes, caused by the electric potential dispersion between the device surface and the substrate, are located in the spacing between two neighboring n+ islands, and greatly enhance the electric field of the buried oxide layer and therefore, effectively increase the device breakdown voltage. Based on a 2−µm −thick buried oxide layer and a 1.5-µm −thick top silicon layer, a breakdown voltage of 1224 V is obtained, resulting in the high electric field (608 V/µm ) of the buried oxide layer.
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86 articles
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