Monolithic Integration of InGaP/AlGaAs/InGaAs Enhancement/Depletion-Mode PHEMTs

The monolithic integration of enhancement- and depletion-mode （E/D-mode） InGaP/AIGaAs/InGaAs pseudomorphic high electron mobility transistors （PHEMTs） with a 1.0μm gate length is presented. Epilayers are grown on SI GaAs substrates using MBE. For this structure, a mobility of 5410cm^2/（V · s） and a sheet density of 1.34 × 10^12 cm^-2 are achieved at room temperature. During the gate fabrication of E/D-mode PHEMTs,a novel twostep technology is applied. The devices with a gate dimension of 1μm × 100μm exhibit good DC and RF performances. Threshold voltages of 0. 2 and -0. 4V,maximum drain current densities of 300 and 340mA/mm,and extrinsic transconductances of 350 and 300mS/mm for E- and D-mode PHEMTs are obtained, respectively. The reverse gatedrain breakdown voltage is -14V for both E- and D-mode. Current-gain cutoff frequencies of 10. 3 and 12.4GHz and power-gain cutoff frequencies of 12.8 and 14.7GHz for E- and D-mode are reported, respectively.

Device Characteristics Comparison Between GaAs Single and Double Delta-Doped Pseudomorphic High Electron Mobility Transistors

The Al 0.24Ga 0.76As/In 0.22Ga 0.78As single delta-doped PHEMT (SH-PHEMT) and double delta-doped PHEMT (DH-PHEMT) are fabricated and investigated.Based on the employment of double heterojunction,double delta doped design,the DH-PHEMT can enhance the carrier confinement,increase the electron gas density,and improve the electron gas distribution,which is beneficial to the device performance.A high device linearity,high transconductance over a large gate voltage swing,high current drivability are found in DH-PHEMT.These improvements suggest that DH-PHEMT is more suitable for high linearity applications in microwave power device.

A Super-Low-Noise,High-Gain MMIC LNA

A two-stage monolithic low noise amplifier is developed for satellite communication applications,using a 0.5μm enhancement PHEMT technology. The on-chip matched amplifier employs lumped elements to reduce the circuit size, and shows a 5012 noise figure less than 0.9dB, gain greater than 26dB, and return loss less than - 10dB in the S-C band range of 3.5 to 4. 3GHz. The noise figure obtained here is the best result ever reported to date of an MMIC LNA with a gain of more than 20dB for the S-C band frequency range. It is attributed to the low noise performance of the enhancement PHEMT transistor and minimized parasitic resistance of the input match network by a common series source inductor and a unique divided resistance at the drain.

Broadband MMIC Power Amplifier for C-X-Ku-Band Applications

A three-stage MMIC power amplifier operating from 6to 18GHz is fabricated using 0.25μm A1GaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor（PHEMT）.The amplifier isfully monolithic,with all matching,biasing,and DC block circuitry included on the chip.Thepower amplifier has an average power gain of 19dB over 6～18GHz.At operation frequenciesfrom 6 to 18GHz,the output power is above 33.3dBm,and the maximum output power of the MMICis 34.7dBm at 10Ghz.The input return loss is less than-10db and the out-put return is lessthan-6dB over operating frequency.This power amplifier has,to our knowledge,the best powergain flatness reported at C-X-Ku-band applications.

Electrochemical lithium storage performance of three-dimensional foam-like biocarbon/MoS2 composites

Molybdenum disulfide(MoS2)was loaded on biocarbon using waste camellia dregs(CDs)as the carbon source,which was further coated with dopamine hydrochloride to construct biocarbon/MoS2 electrode composites.The electrochemical lithium storage performance of the composites with different MoS2 contents was investigated.SEM results demonstrated that the composite had a three-dimensional foam-like structure with MoS2 as the interlayer.XRD and HRTEM tests revealed that MoS2 interlayer spacing in the composite was expanded.XPS analysis showed that new Mo—N bonds were formed in the active material.The electrochemical tests showed that the composite with a MoS2 content of 63%had a high initial specific capacity of 1434 mA·h/g at a current density of 100 mA/g.After a long cycle at a high current,it also showed good cycling stability and the capacity retention was nearly 100%.In addition,it had good lithium ion deintercalation ability in the electrochemical kinetics test.

Enhancement of lithium storage capacity and rate performance of Se-modified MnO/Mn3O4 hybrid anode material via pseudocapacitive behavior

To improve rate and cycling performance of manganese oxide anode material,a precipitation method was combined with thermal annealing to prepare the Mn O/Mn3O4/Se Ox(x=0,2)hybrid anode by controlling the reaction temperature of Mn2O3 and Se powders.At 3 A/g,the synthesized Mn O/Mn3O4/Se Ox anode delivers a discharge capacity of 1007 m A·h/g after 560 cycles.A cyclic voltammetry quantitative analysis reveals that 89.5%pseudocapacitive contribution is gained at a scanning rate of 2.0 m V/s,and the test results show that there is a significant synergistic effect between Mn O and Mn3O4 phases.

Recent advances in pseudocapacitor electrode materials: Transition metal oxides and nitrides

Faraday pseudocapacitors take both advantages of secondary battery with high energy density and supercapacitors with high power density,and electrode material is the key to determine the performance of Faraday pseudocapacitors.Transition metal oxides and nitrides,as the two main kinds of pseudocapacitor electrode materials,can enhance energy density while maintaining high power capability.Recent advances in designing nanostructured architectures and preparing composites with high specific surface areas based on transition metal oxides and nitrides,including ruthenium oxides,nickel oxides,manganese oxides,vanadium oxides,cobalt oxides,iridium oxides,titanium nitrides,vanadium nitrides,molybdenum nitrides and niobium nitrides,are addressed,which would provide important significances for deep researches on pseudocapacitor electrode materials.

Controllable preparation of hierarchical NiO hollow microspheres with high pseudo-capacitance

Nickel oxide(NiO)hollow microspheres with hierarchical structure were fabricated through a process consisting of a self-assembling,hydrothermal reaction and calcination.The prepared NiO hollow microspheres composed of many nanoflakes,are about 2-3μm in diameter.The length of the NiO flakes,having clear edges,is about 500-700 nm,while the thickness is only about 40-50 nm.This indicates that the NiO microspheres possess a hierarchical structure that can provide porous channels to facilitate the transmission of both electrons and electrolyte ions.NiO microspheres exhibit a high specific capacitance of about 1340 F/g at a current density of 1 A/g and high capacitance retention about 96.5%after 1000 cycles.What’s more,the conductive mechanism of nickel oxide for electrochemical capacitor electrodes was also studied.

Influence of the Pseudogap on the Inelastic Neutron Scattering Spectra of the Underdoped Lanthanum Cuprate

The influence of pseudogap on the inelastic neutron scattering spectra of the underdoped lanthanum cuprate is studied on the basis of the model which incorporates both the superconducting state and pseudogap state. It is found that the striking effects of the influence of the pseudogap on the incommensurability of the spin excitation spectrum are that in the superconducting state the pseudogap makes the intensity of the incommensurate peak increase, in the normal state the pseudogap not only makes the intensity of the incommensurate peak increase, but also sharpens the incommensurate peak and increases incommensurability.

Kinetics of celestite conversion to acidic strontium oxalate hydrate in aqueous solution of oxalic acid

Conversion of SrSO4 to acidic strontium oxalate hydrate(H[Sr(C2O4)1.5(H2O)]) in aqueous H2C2O4 solutions proceeds as a consecutive reaction. In the first step of the consecutive reaction, SrSO4 reacts with H2C2O4 and pseudomorphic conversion to SrC2 O4·H2O occurs. In the second step, SrC2 O4·H2O reacts with H2C2O4 to form H[Sr(C2 O4)1.5(H2O)]. Sr(HC2 O4)(C2 O4)0.5·H2 O crystallizes during cooling of the reaction mixture to room temperature if the solution reaches the saturation concentration of (H[Sr(C2O4)1.5(H2O)]. The aims of this study are the derivation of reaction rate equations and the determination of the kinetic parameters such as pre-exponential factor, apparent activation energy and order of H2C2O4 concentration for each reaction step.Fractional conversions of SrSO4 were calculated using the quantitative amounts of dissolved S and Sr. It was determined that the reaction rate increased at the initial time of reaction by increasing the temperature using solutions with approximately same H2C2O4 concentrations. The reaction extends very slowly after a certain time in solutions with low H2C2O4 concentration and ends by the formation of a protective layer of SrC2O4-H2O around the surfaces of solid particles. Fractional conversion of SrSO4 is increased by increasing concentration of H2C2O4 at constant temperature. Kinetic model equations were derived using shrinking core model for each step.

Solutions of Dirac Equation for Makarov Potential with Pseudospin Symmetry

The pseudospin symmetry in the Makarov potential is investigated systematically by solving the Diracequation.The analytical solution for the Makarov potential with pseudospin symmetry is obtained by Nikiforov-Uvarov(N-U)method.The eigenfunctions and eigenenergies are presented with equal mixture of vector and scalar potentials inopposite signs,for which is exact.

First-principles lattice stability of Fe, Ru and Os

Lattice constants, total energies and densities of states of transition metals Fe, Ru and Os with BCC, FCC and HCP structures were calculated by the GGA+PBE functional and the ultrasoft pseudo-potential plane wave method, and compared with those of the first-principles projector augmented wave (PAW) method, CALPHAD method and experimental data. The results show that the lattice stability of this work is △GBCC-HCP>△GFCC-HCP>0, agreeing well with those of PAW method in the first-principles and CALPHAD method except for BCC-Fe. And the densities of state of HCP-Ru and Os have an obvious character of stable phase, agreeing completely with the results of the total energy calculations. Further analyses of atomic population show that the transition rate of electrons from s to p state for HCP, FCC and BCC crystals increases from Fe to Os, and a stronger cohesion, a higher cohesive energy or a more stable lattice between atoms of heavier metals are formed.

First-Principles Study on Native Defect Complexes in InN

We present first-principles calculations of the formation energy of different native defects and their complexes in wurtzite InN using density-functional theory and the pseudopotential plane-wave method. Our calculations are aimed in the three cases： N/In = 1, N/In 〉 1 （N-rich）, and N/In 〈 1 （In-rich）. Our results indicate that the antisite defect has the lowest formation energy under N/In = 1. The formation energy of nitrogen interstitial （nitrogen vacancy） defect is significantly low under the N-rich （In-rich） condition. Thus the antisite defect is an important defect if N/In = 1, and the nitrogen interstitial （nitrogen vacancy） defect is a vital defect under the N-rich （In-rich） condition. The atomic site relaxation around the nitrogen interstitial and vacancy is investigated. Our calculations show that the nitrogen vacancy cannot be observed although it is one of the most important defects in InN. Our results are confirmed by experiments.

A PHEMT Based Wideband LNA for Wireless Applications

This work is about the development of a super low noise amplifier with minimum power consumption and high gain for several wireless applications.The amplifier operates at frequency bands of 0.9-2.4 GHz and can be used in many applications like Wireless local area network(WLAN),WiFi,Bluetooth,ZigBee and Global System for mobile communications(GSM).This new design can be employed for the IEEE 802.15.4 standard in industrial,scientific and medical(ISM) Band.The enhancement mode pseudomorphic high electron mobility transistor PHEMT is used here due to its high linearity,better performance and less noisy operation.The common source inductive degeneration method is employed here to enhance the gain of amplifier.The amplifier produces a gain of more than 17 dB and noise figure of about 0.5 dB.The lower values of S11 and S22 reflect the accuracy of impedance matching network placed at the input and output sides of amplifier.Agilent Advance Design System(ADS) is used for the design and simulation purpose.Further the layout of design is developed on the FR4 substrate.

A New Pseudospectral Method for Calculations of Hydrogen Atom in Arbitrary External Fields

A new pseudospectral method was introduced to calculate wavefunctions and energy levels of hydrogen atom in arbitrary potential. Some results of hydrogen atom in uniform magnetic fields were presented, high accuracy of results was obtained with simple calculations, and our calculations show very fast convergence. It suggests a new methodfor calculations of hydrogen atom in external fields.

The Production of Pseudo Goldstone Boson in Top Quark Rare Decay

We calculate the flavor changing decay in the framework of the topcolor assisted multiscale technicolor model. We find that (a) the branching ratio of is insensitive to and , while it increases quickly as increases; (b) for reasonable ranges of the parameters, the maximum of the branching ratio in this model may reach , seven orders larger compared to the one calculated in the standard model. This might provide an opportunity to detect the rare decay of the top quark in experiments.

Pseudopotentials,Lax Pairs and Bcklund Transformations for Generalized Fifth-Order KdV Equation

Based on the method developed by Nucci, the pseudopotentials, Lax pairs and the mngulanty mamtoia equations of the generalized fifth-order KdV equation are derived. By choosing different coefficient, the corresponding results and the Backlund transformations can be obtained on three conditioners which include Caudrey-Dodd-Cibbon- Sawada-Kotera equation, the Lax equation and the Kaup-kupershmidt equation.

Essence of Pseudogap and Oscillation in High-Temperature Cuprate Superconductor Junction of Pseudogap State

This paper gives methods to calculate the pairing temperature T＊, at which a pseudogap is opened, and the superconducting temperature Tc, at which superconductivity appears, in the high-Te cuprates, and demonstrates directly that at Tc 〈 T 〈 T＊ the pseudogap is the gap of Cooper pair without long-range phase coherence, and at T 〈 Tc there is long-range phase coherence between Cooper pairs. Based on the above clear physical picture on the pseudogap state and our mechanism for the ac Josephson effect, this paper proposes that there should he a novel oscillatory current in P-I-P junction, induced by a constant bias on the junction. Here, P represents the high-Tc curates in the pseudogap state, where Cooper pairs do not have long-range phase coherence, and I represents the thin insulating barrier. This paper conjectures that there is a possible high-temperature superconductivity in the heavily underdoped high-Tc cuprates.

First-principles calculation of structural and thermodynamic properties of titanium boride

The equilibrium lattice parameters, electronic structure, bulk modulus, Debye temperature, heat capacity and Gibbs energy of TiB and TiB2 were investigated using the pseudopotential plane-wave method based on density functional theory (DFT) and the improved quasi-harmonic Debye method. The results show that the total density of states (DOS) of TiB2 is mainly provided by the orbit hybridization of Ti-3d and B-2p states, and the total DOS of TiB is mainly provided by the hybrids bond of Ti-3d and B-2p below the Fermi level and Ti—Ti bond up to the Fermi level. The Ti—B hybrid bond in TiB2 is stronger than that in TiB. Finally, the enthalpy of formation at 0 K, heat capacity and Gibbs free energy of formation at various temperatures were determined. The calculated results are in excellent agreement with the available experimental data.