The fabrication and characterization of 4H SiC power UMOSFETs

The fabrication of 4H-SiC vertical trench-gate metal-oxide-semiconductor field-effect transistors(UMOSFETs) is reported in this paper.The device has a 15-μm thick drift layer with 3×1015 cm-3 N-type doping concentration and a 3.1μm channel length.The measured on-state source-drain current density is 65.4 A/cm2 at Vg = 40 V and VDS = 15 V.The measured threshold voltage(Vth) is 5.5 V by linear extrapolation from the transfer characteristics.A specific on-resistance(Rsp-on) is 181 mΩ·cm2 at Vg = 40 V and a blocking voltage(BV) is 880 V(IDS = 100 μA@880V) at Vg = 0 V.     

NMR study of the electric field gradient in the paramagnetic phase of M<Subscript>3</Subscript>V<Subscript>2</Subscript>O<Subscript>8</Subscript> (M = Co,Ni) compounds

The NMR spectra and the decay of a spin echo signal from ⁵¹V nuclei in Kagome-staircase Co₃V₂O₈ (CVO) and Ni₃V₂O₈ (NVO) single crystals are measured in the temperature range 30–300 K and a magnetic field H ₀ = 20 kOe. The orientation dependences of the ⁵¹V NMR line shape are used to determine the electric field gradient (EFG) parameters, namely, quadrupole frequency ν _Q and asymmetry parameter η. These parameters for NVO and CVO are ν _Q = 180(10) kHz, η = 0.5(1) and ν _Q = 130(10) kHz, η = 0.6(1), respectively. A comparison of the results of calculating EFG tensors with a point charge model and the NMR data indicates that the crystallographically equivalent vanadium atoms in the Ni₃V₂O₈ and Co₃V₂O₈ compounds differ in the EFG axis orientation. M₃V₂O₈ crystals are found to have vanadium positions (V1, V2) with different orientations of the z axis, which specifies the direction of the principal value of EFG (V _zz ): these orientations lie in the bc plane and make an angle of either +51(5)° (V1) or −51(5)° (V2) with axis c. In the temperature range 30–300 K, the EFG tensor components and the local symmetry of the charge surrounding of the vanadium positions in NVO and CVO oxides are found to change insignificantly.     

Cover Picture: Contrib. Plasma Phys. 10/2014

Spatio‐temporal evolution of electron density at 6 microseconds under f = 20 kHz, ε_r = 9.0, RC = 5.0 × 10^–6 cm³ s^–1 and V_appl = 1.7 kV with 50 ppm N₂ impurities in He‐N₂ gas. (Figure 3e of the paper by M.M. Iqbal and M.M. Turner)     

A novel high-voltage light punch-through carrier stored trench bipolar transistor with buried p-layer

A novel high-voltage light punch-through(LPT) carrier stored trench bipolar transistor(CSTBT) with buried p-layer(BP) is proposed in this paper.Since the negative charges in the BP layer modulate the bulk electric field distribution,the electric field peaks both at the junction of the p base/n-type carrier stored(N-CS) layer and the corners of the trench gates are reduced,and new electric field peaks appear at the junction of the BP layer/N drift region.As a result,the overall electric field in the N drift region is enhanced and the proposed structure improves the breakdown voltage(BV) significantly compared with the LPT CSTBT.Furthermore,the proposed structure breaks the limitation of the doping concentration of the N-CS layer(NN CS) to the BV,and hence a higher NN CS can be used for the proposed LPT BP-CSTBT structure and a lower on-state voltage drop(Vce(sat)) can be obtained with almost constant BV.The results show that with a BP layer doping concentration of NBP = 7 × 1015 cm-3,a thickness of LBP = 2.5 μm,and a width of WBP = 5 μm,the BV of the proposed LPT BP-CSTBT increases from 1859 V to 1862 V,with NN CS increasing from 5 × 1015 cm-3 to 2.5 × 1016 cm-3.However,with the same N-drift region thickness of 150 μm and NN CS,the BV of the CSTBT decreases from 1598 V to 247 V.Meanwhile,the Vce(sat) of the proposed LPT BP-CSTBT structure decreases from 1.78 V to 1.45 V with NN CS increasing from 5 × 1015 cm-3 to 2.5 × 1016 cm-3.     

Cover Picture: Contrib. Plasma Phys. 9/2014

Spatio‐temporal evolution of electron density at 6 microseconds under f = 20 kHz, ε_r = 9.0, RC = 5.0 × 10^–6 cm³ s^–1 and V_appl = 1.7 kV with 50 ppm N₂ impurities in He‐N₂ gas. (Figure 3e of the paper by M.M. Iqbal and M.M. Turner)     

Principle of limiting absorption for N-body Schrödinger operators — A remark on the commutator method

We consider a N-body Schrödinger operator H=H ₀+V. The interaction V is given by a sum of pair potentials V _jk(y)(=V _jk ^s +V _jk ^l ), y R³. We assume that: V _jk ^s =O(|y|^-(1+p)), p>0, as |y| for the short-range part V _jk ^s ; for the long-range part V _jk ^l . Under this assumption, we prove the principle of limiting absorption for H. The obtained result is essentially as good as those obtained in the two-body case. The proof is done by a slight modification of the remarkable commutator method due to Mourre.     

Electrical transport in ferroelectric Pb[(Fe1/3Sb2/3) x Ti y Zr z ]O3 ceramics

In this article, the studies of the polarization currents and current–voltage characteristics (J–V) are presented. The measurements of the J–V in low and high temperatures as well as at low and high voltages have permitted to recognize certain details of local energy levels in forbidden gap. It has been possible to calculate energy trap levels and their concentration. Calculated trap energy and concentration, under the condition of single trap energy levels, are equal: E _t = 0.55 eV, N _t = 2.97 · 10²³ m^?3 for the sample y = 0.44 and E _t = 0.59 eV, N _t = 1.5 · 10²³ m^?3 for the sample y = 0.47. Knowing the J–V characteristic and the Seebeck coefficient the carriers concentration and their mobility can also be calculated. The carriers concentration and their mobility are equal: n = 3.8 · 10¹⁸ m^?3, µ = 1.4 · 10^?12 m² V^?1 · s^?1 for sample y = 0.44 and n = 6.9 · 10¹⁶ m^?3, µ = 1.3·10^?11 m² V^?1 · s^?1 for the sample y = 0.47.     

微晶硅薄膜晶体管稳定性研究

对有源区处于结构过渡区的微晶硅底栅薄膜晶体管，测试其偏压衰退特性时，观察到一种“自恢复”的衰退现象.当栅和源漏同时施加10 V的偏压时，测试其源-漏电流随时间的变化，发现源-漏电流先衰减、而后又开始恢复上升的反常现象.而当采用栅压为10 V、源-漏之间施加零偏压的模式时，源-漏电流随时间呈先是几乎指数式下降、随之是衰退速度减缓的正常衰退趋势.就此现象进行了初步探讨. 关键词： 过渡区硅材料 微晶硅薄膜晶体管 稳定性 自恢复衰退     

Equation of state and thermal expansivity of LiF and NaF

The high-pressure and high-temperature behaviors of LiF and NaF have been studied up to 37 GPa and 1000 K. No phase transformations have been observed for LiF up to the maximum pressure reached. The B1 to B2 transition of NaF at room temperature was observed at ～28 GPa, this transition pressure decreases with temperature. Unit-cell volumes of LiF and NaF B1 phase measured at various pressures and temperatures were fitted using a P–V–T Birch–Murnaghan equation of state. For LiF, the determined parameters are: α₀ = 1.05 (3)×10^?4 K^?1, dK/dT = ?0.025 (2) GPa/K, V ₀ = 65.7 (1) Å³, K ₀ = 73 (2) GPa, and K′ = 3.9 (2). For NaF, α₀ = 1.34 (4)×10^?4 K^?1, dK/dT = ?0.020 (1) GPa/K, V ₀ = 100.2 (2) Å³, K ₀ = 46 (1) GPa, and K′ = 4.5 (1).     

TDPAD measurements with highly oriented pyrolytic graphite using the19F(p,p′)19F* and19F(α, n)22Na* reactions

The TDPAD technique has been used to investigate quadrupole interactions of¹⁹F*(E _x =197 keV,J ^π=5/2⁺,T _1/2=88.5 ns) and²²Na*(E _x =583 keV,J ^π=1⁺,T _1/2=243 ns) in highly oriented pyrolytic graphite (HOPG). For¹⁹F* a single static quadrupole interaction was found with field gradientV _ZZ =3.24(19) × 10¹⁸ V/cm². For the case of²²Na* no quadrupole interaction was detected, leading to the conclusion that |QV _ZZ |<5.2(5) × 10¹⁵ b V/cm². TakingQ=0.06 b for the 583 keV state on the basis ofB(E2) measurements and theoretical estimates, we find that |V _ZZ | <8.7(8) × 10¹⁶ V/cm². The data demonstrate the advantages of using HOPG as a host material for the study of quadrupole interactions. Former Central Bureau for Nuclear Measurements (CBNM).     

A Note on the Koszul Complex in Deformation Quantization

The aim of this short note is to present a proof of the existence of an A _∞-quasi-isomorphism between the A _∞-S(V ^*)-ù(V){\wedge(V)} -bimodule K, introduced in Calaque et al. (Bimodules and branes in deformation quantization, 2009), and the Koszul complex K(V) of S(V ^*), viewed as an A _∞-S(V ^*)-ù(V){\wedge(V)} -bimodule, for V a finite-dimensional (complex or real) vector space.     

Microscopic magnetic properties of nonstoichiometric V2O3+x—NMR and inelastic spin-flip neutron scattering measurements

The local magnetic properties of the V sites in the nonstoichiometric V₂O_3+x (0 ? x <0.08) have been examined by nuclear magnetic resonance and inelastic spin-flip neutron scattering techniques. The samples with x = 0.01 and 0.02 show a paramagnetic metal (PM)-antiferromagnetic insulator (AFI) transition. In the AFI phase, two distinct ⁵¹V NMR signals with hyperfine fields H_n = 184.9±0.5 kOe and 71±1 kOe were observed at 1.8 K, which were assigned as due to V³⁺ and V³⁺ sites, respectively. On the other hand, the samples with x = 0.04 and 0.06 were metallic down to 1.4K, and showed a paramagnetic (PM)-antiferromagnetic (AFM) transition at about 10 K. In these samples, a ⁵¹V NMR signal with H_n = 58±2 k0e and one with 〈H_n〉 = 9kOe were observed at 1.8 K, which were assigned as due to V³⁺-like sites and the matrix V sites, respectively. These results are entirely consistent with those obtained from the neutron experiment. We propose that in the metallic phase (0.04 ? x < 0.08) the minority V⁴⁺-like sites are magnetically localized in the delocalized V matrix and may be responsible for the antiferromagnetic long range order below 10 K.     

Structural phase transitions in Pd0.8 Si0.2 and Pd0.75 Si0.20 Ag0.05 alloys observed by pac

The phase transition in the alloys Pd_0.8 Si_0.2 and Pd_0.75 Si_0.20 Ag_0.05 have been investigated through the quadrupole interaction of¹¹¹Cd impurities. The quadrupole interactions were measured by means of the TDPAC technique from room temperature up to about 870 K. The variation of the quadrupole interaction with temperature in the alloy PdSiAg shows aT ^3/2 dependence below and above 629 K, with coefficientsB=5.43(25)·10⁻⁵ K^−3/2 andB=3.70(15)·10⁻⁵ K^−3/2, respectively. This demonstrates that the alloy undergoes a phase transition around 629 K. The existence of two electric field gradients observed in the alloy PdSi,V _zz (1)=3.47(54)·10¹⁷ V/cm² andV _zz (2)=2.29(36)·10¹⁷ V/cm², indicates that there are two different¹¹¹Cd sites. The corresponding fractionsf ₁ andf ₂ strongly depend on temperature. Below 520 K, most¹¹¹Cd nuclei are subject to the higher EFGV _zz (1) (f ₁≈70%), whereas above 520 Kf ₁ falls rapidly to zero andV _zz (2) becomes dominant. The temperature dependences of thef ₁ andf ₂ reveal a picture of the phase transition between the two crystal structures.     

The theory and experiment of very-long-wavelength 256×1 GaAs/Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>As quantum well infrared detector linear arrays

The 256×1 linear array of multiple quantum wells infrared photodetector (QWIP) is designed and fabricated for the peak response wavelength at λ _P = 14.6 μm. The response spectral width is bigger than 2.2 μm. The two-dimensional (2D) diffractive coupling grating has been formed on the top QWIP photosensitive pixel for coupling the infrared radiation to the infrared detective layers. The performance of the device at V _B = 3 V and T = 45 K has the responsibility 4.28×10⁻² (A/W), the blackbody detectivity D _b* = 5.14×10⁹ (cm·Hz^1/2/W), and the peak detectivity D _λ * = 4.24× 10¹⁰ (cm·Hz^1/2/W). The sensor pixels are connected with CMOS read out circuit (ROC) hybridization by indium bumps. When integral time is 100 μs, the linear array has the effective pixel of QWIP FPA N _ef of 99.2%, the average responsibility (V/W) of 3.48×10⁶ (V/W), the average peak detectivity D _λ * of 8.29×10⁹ (cm·Hz^1/2/W), and the non-uniformity U_R of 5.83%. This device is ready for the thermal image application. Supported by the National Natural Science Foundation of China (Grant No. 10374095)     

A 20 nm gate-length ultra-thin body p-MOSFET with silicide source/drain

As the scaling of CMOS transistors extends to the sub-20 nm regime, the most challenging aspect of device design is the control of the off-state current. The traditional methods for controlling leakage current via the substrate doping profile will be difficult to implement at these dimensions. A promising method for controlling leakage in sub-20 nm transistors is the reduction in source-to-drain leakage paths through the use of a body region which is significantly thinner then the gate length, with either a single or a double gate. In this paper we present ultra-thin body PMOS transistors with gate lengths down to 20 nm fabricated using a low-barrier silicide as the source and drain. Calixarene-based electron-beam lithography was used to define critical device dimensions. These transistors show 260 μ A μ m ^{− 1}on-current and on/off current ratios of 10⁶, for a conservative oxide thickness of 40 Å and | V_g − V_t| = 1.2 V. Excellent short-channel effect, with only 0.2 V reduction in | V_t| is obtained in devices with gate lengths ranging from 100 to 20 nm.     

V替代Mn对La_(0.45)Ca_(0.55)MnO_3电荷有序相及自旋玻璃态的影响

用固相反应法制备了La0.45Ca0.55Mn1-xVxO3(x=0.00,0.10)多晶样品.通过X射线衍射谱、质量磁化强度-温度曲线、电子自旋共振谱,研究了V5+替代Mn3+/Mn4+对La0.45Ca0.55MnO3电荷有序相和自旋玻璃态的影响.实验结果表明,当x=0.10时,不仅母体的电荷有序相基本破坏,而且母体在40K左右出现的自旋玻璃态也被融化.电荷有序相被破坏的主要原因是用V5+替代Mn3+/Mn4+后,增加了Mn3+与Mn4+的比例,使铁磁双交换作用优于反铁磁超交换作用;自旋玻璃态的融化是由于V替代Mn后破坏了反铁磁背景下有少量铁磁成分的自旋玻璃态的形成条件.     

Optical and Photoelectric Inhomogeneity of CdTe:V Crystals

The optical and photoelectric properties of CdTe:V crystals with the doping impurity concentration N _V = 5·10¹⁸–5·10¹⁹ cm^–3 are investigated and the possibility of their use as a photorefractive material is considered. As is seen from the spectra of optical transmission, the crystals of both types possess high transparency (50–65%), which for CdTe:V specimens with N _V = 5·10¹⁹ cm^–3 decreases sharply and in the range 12–14 m does not exceed 5%, whereas for CdTe:V crystals with vanadium concentration of 5·10¹⁸ cm^–3 such a value of transmission remains unchanged up to 25 m, implying a good optical quality of the latter crystals and their possible application in the spectral range 1.06–1.25 m in modern fiber-optic communication lines.     

Changes produced in etching parameters of CR-39 by high-dose pre- and post-γ irradiation

The effect of post- and pre-high doses of γ–radiation in CR-39 plastic detectors has been studied in the dose range of 3×10¹?10⁶ Gy. Some properties like bulk-etch rate (V _B), track-etch rate (V _T), sensitivity (V _T/V _B) and efficiency have been found out for different gamma doses from a ⁶⁰Co source in CR-39. It is found that V _B and V _T remain almost invariant up to gamma doses of 10⁴ Gy. Then they start increasing slowly till 10⁵ Gy. Between 10⁵ Gy and 10⁶ Gy there is a sharp increase of V _B and V _T values for pre- and post-gamma exposed samples. The present data are compared with the previous literature.     

DPAC study of radiation damage in178W recoil implanted silicon

The annealing behaviour of radiation damage in¹⁷⁸W recoil implanted n-type Si is studied from 295 to 641 K by the differential perturbed angular correlation method (DPAC), using¹⁷⁸Hf as probe nuclei for the first time. Preliminary results suggest that oxygen-vacancy (O-V) pairs are observed, which give rise to a quadrupole interaction characterized by |V _zz|=5.41×10¹⁸ V/cm² (v _Q=2550 MHz). The probe nuclei also experience an electric field gradient (EFG) due to distant defects.     

Titanium Doping to Enhance Thermoelectric Performance of 19-Electron VCoSb Half-Heusler Compounds with Vanadium Vacancies

The 19-electron VCoSb compounds are actually composites of an off-stoichiometric half-Heusler phase and impurities. Here the compositional adjustment is systematically studied in V_1−xCoSb to obtain single-phase V_0.955CoSb. Hall measurements suggest that such a V vacancy, as well as Ti doping, can optimize the carrier concentration, which decreases from ≈11.3 × 10²¹ cm⁻³ for VCoSb to ≈6.3 × 10²¹ cm⁻³ for V_0.755Ti_0.2CoSb. Low sound velocity contributes to the intrinsically low lattice thermal conductivity for VCoSb-based materials. The high Ti-dopant content results in enhanced point-defect scattering, which further decreases the lattice thermal conductivity. Finally, the optimized n-type V_0.855Ti_0.1CoSb is found to reach a peak ZT of ≈0.7 at 973 K. The work demonstrates that the VCoSb-based half-Heuslers are promising thermoelectric materials.