Physical simulations and experimental results of 4H—SiC MESFETs on high purity semi-insulating substrates

In this paper we report on DC and RF simulations and experimental results of 4H--SiC metal semiconductor field effect transistors (MESFETs) on high purity semi-insulating substrates. DC and small-signal measurements are compared with simulations. We design our device process to fabricate n-channel 4H--SiC MESFETs with 100~μm gate periphery. At 30~V drain voltage, the maximum current density is 440~mA/mm and the maximum transconductance is 33~mS/mm. For the continuous wave (CW) at a frequency of 2~GHz, the maximum output power density is measured to be 6.6~W/mm, with a gain of 12~dB and power-added efficiency of 33.7％. The cut-off frequency (f_T) and the maximum frequency (f_max) are 9~GHz and 24.9~GHz respectively. The simulation results of f_T and f_max are 11.4~GHz and 38.6~GHz respectively.     

Investigation of SOI Substrates Incorporated with Buried MoSi2 for High Frequency SiGe HBTs

Highly arsenic-doped Si-on-insulator （SOI） substrate incorporated with buried MoSi2 layers is fabricated aiming at decreasing the collector series resistance of SiGe heterojunction bipolar transistors （HBTs） on SOI, thereby enhancing cutoff frequency （fT） performance and increasing the maximum value of fT （fTMAX ）. The .fT performance at medium current is enhanced and current required for fT = 15 GHz is reduced by half The value of fTMAX is improved by 30%.     

Electrical Studies on Pentacene Thin Film Transistors with Different Channel Widths

In order to conduct electrical studies on organic thin film transistors, top-contact devices are fabricated by growing polycrystalline films of freshly synthesized pentacene over Si/SiO2 substrates with two different channel widths under identical conditions. Reasonable field effect mobilities in order of 10^-2-10^-3 cm^2V^-1s^-1 are obtained in these devices. An elaborative electrical characterization of all the devices is undertaken to study the variance in output saturation current, field effect mobility, and leakage current with aging under ambient conditions. As compared to the devices with longer channel width, the devices with shorter channel width exhibit better electrical performance initially. However, the former devices sustain the moderate performance much longer than the latter ones.     

Influence of the size of the interpolated cation upon the CMR properties of the perovskites Nd0.7Ca0.3−xSrxMnO3−δ

The systematic study of the manganese perovskite Nd_0.7Ca_0.3-xSr_xMnO_3-' has allowed colossal magnetoresistance effects (CMR) with resistance ratios (RR), R_B=0/R_B=5T, up to 10⁴ at 60rK in a field of 5 tesla to be evidenced. The influence of the mean size of the interpolated cation (Nd, Ca, Sr), on the magnitude of the RR ratios, has been demonstrated for the first time: RR goes through a maximum for a particular value of the mean radius of the interpolated cation. This effect seems to be correlated with the evolution of the cell volume that exhibits a singular point around x=0.085. A second important feature deals with the irreversibility of the CMR effect at low temperature that decreases as T increases and disappears at T_max. It is also remarkable that for A(T) curves characterized by a maximum, T_max not only increases as the size of the interpolated cation increases, but also as the magnitude of the applied magnetic field increases.     

Ultraviolet Phototransistors on AlGaN/GaN Heterostructures

We report on the fabrication and characterization of phototransistors based on AIGaN/GaN heterostructure grown over 6H-SiC substrates. The device has two functions： as a high electron mobility transistor （HEMT） and an ultraviolet photodetector at the same time. As an HEMT, its maximum transconductance is 170mS/ram, while the minimum cutoff frequency fT and the maximum oscillation frequency fm are 19 and 35 GHz, respectively. As a photodetector, the device is visible blind, with an ultraviolet/green contrast of three orders of magnitude, and a responsivity as high as 1700 A/W at the wavelength of 362nm.     

ANALYSIS OF QUASI-△33 DOORWAY STATE MODEL IN π NUCLEUS SCATTERING

Under Quasi-△₃₃ Doorway state model of π nucleus scattering, the differential cross sections and total cross sections of elastic π-⁴He and π-⁴⁰Ca at the different incident energies, (T_x^lab=110, 150, 180, 220, 260 MeV for π-⁴He, T_x^lab=115.5, 163.3, 241.0 MeV for π-⁴⁰Ca) are calculated. The approximate agreement between the theoretical results and experimential data is arrived at.We evaluate further the correction of spin-orbite coupling effects for π-⁴He, and the better agreements with experimential data are obtained.     

Polarized Micro-Raman Study of the Temperature-Induced Phase Transition In 0.67 Pb（Mg1/3Nb2/3）O3-0.33PbTiO3

Polarized Raman spectra of ferroelectric relaxor 0.67Pb（Mg1/3Nb2/3）O3-0.33PbTiO3 （0.67PMN-0.33PT） single crystal are systematically investigated in a wide temperature range from -196 to 600℃ by micro-Raman scattering technique. The results clearly reveal that there are two structural phase transitions in such composite ferroelectric relaxor： the rhombohedral-tetragonal （R- T） phase transition and the tetragonal-cubic （T- C） phase transition. The former occurs at about TR-T =34℃, corresponding to the vanishing of the soft A1 mode at 106cm^-1 recorded in the parallel polarization. The latter appears at about TT-C = 144℃, which can be verified with the vanishing of mode at 780cm^-1 measured in the crossed polarization.     

压力对GdoBr:Eu晶场参数的影响

 在室温下测量了GdoBr:Eu的常压和高压荧光谱，光谱范围在13 000~21 500 cm^-1之间，压力至12 GPa。由光谱数据得到了Eu³⁺晶场能级随压力的变化曲线。⁷F_0～5能级随压力的变化规律比较复杂，而⁵D_0~2各能均随压力的升高几乎线性地降低。在基态谱项⁷F的49个状态上进行了晶场拟合计算，所得常压下的5个非零晶场参数分别为：B₀²＝-1 124.0 cm^-1，B₀⁴＝-969.6 cm^-1，B₄⁴＝827.9 cm^-1，B₀⁶＝889.6 cm^-1，B₄⁶＝377.0 cm^-1。高压下的计算结果表明，B₀⁴、B₀⁶这两个晶场参数随压力的增加而增大，B₄⁶随压力的增加而减小，而B₀²、B₄⁴随压力的变化有些起伏。晶场强度在8 GPa以下随压力增加而减小，其后开始变强。     

Fabrication of 160-nm T-gate metamorphic AlInAs/GaInAs HEMTs on GaAs substrates by metal organic chemical vapour deposition

The fabrication and performance of 160-nm gate-length metamorphic AlInAs/GaInAs high electron mobility tran-sistors (mHEMTs) grown on GaAs substrate by metal organic chemical vapour deposition (MOCVD) are reported. By using a novel combined optical and e-beam photolithography technology, submicron mHEMTs devices have been achieved. The devices exhibit good DC and RF performance. The maximum current density was 817 mA/mm and the maximum transconductance was 828 mS/mm. The non-alloyed Ohmic contact resistance Rc was as low as 0.02 Ω- mm. The unity current gain cut-off frequency (fT) and the maximum oscillation frequency (fmax) were 146 GHz and 189 GHz, respectively. This device has the highest fT yet reported for a 160-nm gate-length HEMTs grown by MOCVD. The output conductance is 28.9 mS/mm, which results in a large voltage gain of 28.6. Also, an input capacitance to gate-drain feedback capacitance ratio, Cgs/Cgd, of 4.3 is obtained in the device.     

COULOMB EFFECT IN π-NUCLEUS SCATTERING AT LOW ENERGY

The importance of Coulomb effect for π-¹²C, ¹⁶O scatterings is studied at incidentenergy T_π=80, 70, 50, MeV. Results show that the discrepancy between the data andthe calculation that appears in differential cross section for T_π=50 MeV in referenceis not attributed to ignoring Coulomb effect. The Coulomb effect in such energy regionis negligible, except small angle region in the differential cross sections at. T_π=50 MeV.     

Improved Performance of Organic Thin Film Transistor with an Inorganic Oxide/Polymer Double-Layer Insulator

We employ the Ta2Os/PVP （poly-4-vinylphenol） double-layer gate insulator to improve the performance of pentacene thin-film transistors. It is found that the double-layer insulator has low leakage current, smooth surface and considerably high capacitance. Compared to Ta205 insulator layers, the device with the Ta2Os/PVP doublelayer insulator exhibits an enhancement of the field-effect mobility from 0.21 to 0.54 cm2/Vs, and the decreasing threshold voltage from 4.38 V to -2.5 V. The results suggest that the Ta2Os/PVP double-layer insulator is a potential gate insulator for fabricating OTFTs with good electrical performance.     

Chiral Lagrangian Treatment of 0^＋＋ Mesons and 0^＋＋ Glueballs

Within the framework of a nonlinear chiral Lagrangian the mass spectra and the decay properties of 0^＋＋ states below 2 GeV are studied. Assuming that f0（980）, a0（980）, K0（1430）, and f0（1500） comprise an SU（3） nonet, we make a detailed prediction about the static properties of the 0^＋＋ mesons. The substructure analysis of these states in terms of two- and four-quark components as well as a glueball component is carried out. We also consider the interaction Lagrangian and provide a preliminary study of the strong and radiative decays of the 0＋＋ mesons. The scalar glueball masses and partial widths are also presented. In view of the fact that few data of 0＋＋ mesons are clearly given in the present PDG （Particle Data Group） list and that the four-quark content of mesons is a hot issue both experimentally and theoretically, the predicted results of the paper may be helpful for upcoming experimental and theoretical studies of these mesons.     

Experimental Study of Resonance f2(1270) in the J/ψ Hadronic Decay

Based on the 2.5 million J/ψ's collected by the BES at BEPC,through the hadronic decay J/ψ→ωf₂(1270),f₂(1270)→π⁺π^－,ω→π⁺π^－π⁰,the properties of the resonance f₂(1270) are studied:its mass,width,and branching ratio.the angular distribution is fitted with maximum likelihood methood,determining its.J^PC=2⁺⁺ and giving in the first time the helicity amplitude ratios of this process as:x=0.99±0.29; y=－0.24±0.17; z₁=0.90±0.57;z₂=0.56±0.22.     

水绿矾的状态方程和高压熔化

 用阻抗匹配法和压电探针技术测量了初始密度为1.714 g/cm³（孔隙率α=ρ₀/ρ₀₀=1.898/1.714=1.107）的水绿矾（FeSO₄·7H₂O）的冲击压缩线,发现其在0～100 GPa范围内存在两个明显相区：含有部分熔融的低压相和完全熔化的高压相。在两个相区内,冲击波速度D和波后粒子速度u可分别描述为：D=0.59+2.06u（u<3.12 km/s）和D=3.18+1.223u（u≥3.12 km/s）。从冲击压缩数据出发,用欧拉有限应变理论得到了其等熵状态方程。其熔化方程可用p_m(GPa) =0.159(T_m(K)/1000)^6.3371+0.69来近似描述。     

A novel double-recessed 4H-SiC MESFET with partly undoped space region

In this paper, a novel double-recessed 4H-SiC metal semiconductor field effect transistor (MESFET) with partly undoped space region (DRUS-MESFET) is introduced. The key idea in this work is to improve the DC and RF characteristics of the device by introducing an undoped space region. Using two-dimensional and two-carrier device simulation, we demonstrate that breakdown voltage (V_BR) increases from 109 V in conventional double recessed MESFET (DR-MESFET) structure to 144.5 V in the DRUS-MESFET structure due to the modified channel electric field distribution of the proposed structure. The maximum output power density of the DRUS-MESFET structure is about 25.4% larger than that of the DR-MESFET structure. Furthermore, lower gate-drain capacitance (C_GD), higher cut-off frequency (f_T), larger maximum available gain (MAG), and higher maximum oscillation frequency (f_max) are achieved for the DRUS-MESFET structure. The results show that the f_max and f_T of the proposed structure improve 95.6% and 13.07% respectively, compared with that of the DR-MESFET structure. Also, the MAG of the DRUS-MESET is 4.5 dB higher than that of the DR-MESFET structure at 40 GHz. The results show that the DRUS-MESFET structure has superior electrical characteristics and performances in comparison with the DR-MESFET structure.     

Simultaneous Generation of Multi-Wavelength Laser from Nd:YAG Crystals in a Cruciform Cavity

A cruciform cavity is presented for multi-wavelength laser generation. On the basis of considering the optimal power ratio and good spatial overlap of the two fundamental beams, the maximum output power of 589 nm laser reaches 3.5 W when the pumping power of Nd：YAG A and Nd：YAG B are 311.5 W and 261.8 W, respectively. At the same time, the other wavelength lasers are also obtained with the output power distribution of 2.5 W at 66Onto, 15 W at 532nm, lOOmW at 1319nm and 240mW at 1064nm. The corresponding beam quality factors are M^2 x = 4.93, M^2 y = 5.01 at 589nm, M^2z = 4.51, M^2 y = 4.85 at 660hm, and M^2 x = 4.12, M^2 y = 3.96 at 532nm, respectively. The instabilities of the three visible lights are measured, which are also less than 2% within three hours.     

Raman and X-Ray Investigation of Pyrope Garnet （Mg0.76Fe0.14Ca0.10）3Al2Si3O12 under High Pressure

The compressional behavlour of natural pyrope garnet is investigated by using angle-dlspersive synchrotron radiation x-ray diffraction and Raman spectroscopy in a diamond anvil cell at room temperature. The pressureinduced phase transition does not occur under given pressure. The equation of state of pyrope garnet is determined under pressure up to 25.3 GPa. The bulk modulus KTO is 199 GPa, with its first pressure derivative K′TO fixed to 4. The Raman spectra of pyrope garnet are studied. A new Raman peak nearly at 743 cm^-1 is observed in a bending vibration of the SiO4 tetrahedra frequency range at pressure of about 28 GPa. We suggest that the new Raman peak results from the lattice distortion of the SiO4 tetrahedra. All the Raman frequencies continuously increase with the increasing pressure. The average pressure derivative of the high frequency modes （650-1000 cm^-1） is larger than that of the low frequency （smaller than 650 cm^-1）. Based on these data, the mode Grǖneisen parameters for pyrope are obtained.     

Fabrication and Characterization of SmCo5/Fe65Co35 and SmCo5/Fe Composite Spring Exchange Magnets

SmCo5/Fe65Co35 and SmCo5/Fe spring exchange magnets are fabricated by dc magnetron sputtering on MgO substrates and 100-nm-thick Si3N4 membranes, respectively. The base pressure of sputtering chamber is kept below 10^-7 Tort, and Ar pressure is 3 to 8mTorr. The samples are characterized by an x-ray diffractometer, a superconducting quantum interference magnetometer, and high resolution magnetic soft x-ray microscopy. We obtain the complete exchange coupling and single phase behaviour of composite magnets. The （BH）max value achieved is 28.8 MGOe.     

Dielectronic Recombination of Sn^10＋ Ions and Related Satellite Spectra

Based on the multi-configuration Dirac-Fock method, theoretical calculations are carried out for the dielectronic recombination （DR） rate coefficients and the collision excitation rate coefficients of Sn^10＋ ions. It is found that the total DR rate coefficient has its maximum value between 10eV and 100eV and is greater than either the radiative recombination or three-body recombination rate coefficients （the number of free electrons per unit is 10^21 cm^3） for the ease of Te 〉 1 eV. Therefore, DR can strongly influence the ionization balance of laser produced multi-charged tin ions. The related dieleetronie satellite cannot be ignored at low temperature Te 〈 5 eV.     

MEASUREMENTS OF ANGULAR MOMENTUM EFFECT OF FISSION BARRIER

The fission cross sections and the evaporation residue cross sections for ¹²C+²⁰⁹Bi and ¹⁴N+Pb reactions were measured with the gold surface barrier silicon detectors and the mica nuclear track detectors.The critical angular momentum l_er was deduced from the measured evaporation residue cross section σ_er on the basis of the sharp-off model.The fission barrier with the particular angular momentum i derived from the condition Γ_f/Γ_n=1 at l=l_e The angular momentum effect of the fission barrier was studied experimentally.