High-performance 4H-SiC junction barrier Schottky diodes with double resistive termination extensions

4H-SiC junction barrier Schottky (JBS) diodes with a high-temperature annealed resistive termination extension (HARTE) are designed, fabricated and characterized in this work. The differential specific on-state resistance of the device is as low as 3.64 m ·cm2 with a total active area of 2.46×10-3 cm2 . Ti is the Schottky contact metal with a Schottky barrier height of 1.08 V and a low onset voltage of 0.7V. The ideality factor is calculated to be 1.06. Al implantation annealing is performed at 1250℃ in Ar, while good reverse characteristics are achieved. The maximum breakdown voltage is 1000 V with a leakage current of 9×10-5 A on chip level. These experimental results show good consistence with the simulation results and demonstrate that high-performance 4H-SiC JBS diodes can be obtained based on the double HARTE structure.     

Non-ideal effect in 4H-SiC bipolar junction transistor with double Gaussian-doped base

The non-ideal effect of 4H–Si C bipolar junction transistor(BJT) with a double Gaussian-doped base is characterized and simulated in this paper.By adding a specific interface model between Si C and Si O2,the simulation results are in good agreement with the experiment data.An obvious early effect is found from the output characteristic.As the temperature rises,the early voltage increases,while the current gain gradually decreases,which is totally different from the scenario of silicon BJT.With the same effective Gummel number in the base region,the double Gaussian-doped base structure can realize higher current gain than the single base BJT due to the built-in electric field,whereas the early effect will be more salient.Besides,the emitter current crowding effect is also analyzed.Due to the low sheet resistance in the first highlydoped base epilayer,the 4H–BJT with a double base has more uniform emitter current density across the base-emitter junction,leading to better thermal stability.     

Effect of emitter layer doping concentration on the performance of a silicon thin film heterojunction solar cell

A novel type of n/i/i/p heterojunction solar cell with a-Si:H(15nm)/a-Si:H(10nm)/ epitaxial c-Si(47μm)/epitaxial c-Si(3μm) structure is fabricated by using the layer transfer technique, and the emitter layer is deposited by hot wire chemical vapour deposition. The effect of the doping concentration of the emitter layer S d (Sd =PH3 /(PH3 +SiH4 +H2 )) on the performance of the solar cell is studied by means of current density-voltage and external quantum efficiency. The results show that the conversion efficiency of the solar cell first increases to a maximum value and then decreases with S d increasing from 0.1% to 0.4%. The best performance of the solar cell is obtained at S d = 0.2% with an open circuit voltage of 534 mV, a short circuit current density of 23.35mA/cm2 , a fill factor of 63.3%, and a conversion efficiency of 7.9%.     

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.     

Modeling of 4H--SiC multi-floating-junction Schottky barrier diode

This paper develops a new and easy to implement analytical model for the specific on-resistance and electric field distribution along the critical path for 4H-SiC multi-floating junction Schottky barrier diode. Considering the charge compensation effects by the multilayer of buried opposite doped regions, it improves the breakdown voltage a lot in comparison with conventional one with the same on-resistance. The forward resistance of the floating junction Schottky barrier diode consists of several components and the electric field can be understood with superposition concept, both are consistent with MEDICI simulation results. Moreover, device parameters are optimized and the analyses show that in comparison with one layer floating junction, multilayer of floating junction layer is an effective way to increase the device performance when specific resistance and the breakdown voltage are traded off. The results show that the specific resistance increases 3.2 mΩ·cm 2 and breakdown voltage increases 422 V with an additional floating junction for the given structure.     

Thermal resistance matrix representation of thermal effects and thermal design of microwave power HBTs with two-dimensional array layout

Based on the thermal network of the two-dimensional heterojunction bipolar transistors(HBTs) array, the thermal resistance matrix is presented, including the self-heating thermal resistance and thermal coupling resistance to describe the self-heating and thermal coupling effects, respectively.For HBT cells along the emitter length direction, the thermal coupling resistance is far smaller than the self-heating thermal resistance, and the peak junction temperature is mainly determined by the self-heating thermal resistance.However, the thermal coupling resistance is in the same order with the self-heating thermal resistance for HBT cells along the emitter width direction.Furthermore, the dependence of the thermal resistance matrix on cell spacing along the emitter length direction and cell spacing along the emitter width direction is also investigated, respectively.It is shown that the moderate increase of cell spacings along the emitter length direction and the emitter width direction could effectively lower the self-heating thermal resistance and thermal coupling resistance,and hence the peak junction temperature is decreased, which sheds light on adopting a two-dimensional non-uniform cell spacing layout to improve the uneven temperature distribution.By taking a 2 × 6 HBTs array for example, a twodimensional non-uniform cell spacing layout is designed, which can effectively lower the peak junction temperature and reduce the non-uniformity of the dissipated power.For the HBTs array with optimized layout, the high power-handling capability and thermal dissipation capability are kept when the bias voltage increases.     

点接触放大器的放大作用

For an n-type transistor, with copper and phosphor-bronze whiskers respectively for its emitter and collector, as the result of electrical forming, the emitter should have a metal-p-n structure. In the first part of this paper, the forward characteristics of such a structure is analized for the whole range of current, with special reference to the variation of the emission ratio γ with the current. The design requirement of a flat γ-I_e curve is discussed. The second part of the paper contains an analysis of current amplification of the collector. The structure assumed is a metal-p-n junction, the diffusion of phosphorus into the structure causing a high barrier for holes at the metal contact. By combining the result of the two parts, a resultant a-I_e, relation is calculated for a typical case. The main factors affecting the performance of the transistor and means of its improvement are discussed in some detail.     

Effect of the annealing temperature on the long-term thermal stability of Pt/Si/Ta/Ti/4H–SiC contacts

The Pt/Si/Ta/Ti multilayer metal contacts on 4H–Si C are annealed in Ar atmosphere at 600°C–1100°C by a rapid thermal processor(RTP). The long-term thermal stability is evaluated by aging the annealed contact at 600°C in air. The contact's properties are determined by current–voltage measurement, and the specific contact resistance is calculated based on the transmission line model(TLM). Transmission electron microscope(TEM) and energy-dispersive x-ray spectrometry(EDX) are used to characterize the interface morphology, thickness, and composition. The results reveal that a higher annealing temperature is favorable for the formation of an Ohmic contact with a lower specific contact resistance, and causes the rapid degradation of the Ohmic contact in the aging process.     

Characteristics of Nb/Al superconducting tunnel junctions fabricated using ozone gas

To improve the energy resolution(?E) of Nb/Al superconducting tunnel junctions(STJs), an ozone(O3) oxidation process has been developed to fabricate a thin defect-free tunnel barrier that simultaneously shows high critical current JC 1000 A/cm2 and high normalized dynamic resistance RDA 100 M?·μm2, where A is the size of the STJ. The 50-μm2 STJs produced by O3 exposure of 0.26 Pa·min with an indirect spray of O3 gas, which is a much lower level of exposure than the O2 exposure used in a conventional O2 oxidation process, exhibit a maximum JC= 800 A/cm2 and a high RDA = 372 M? ·μm2. The 100-pixel array of the 100-μm2STJs produced using the same O3 oxidation conditions exhibits a constant leak current I leak= 14.9 ± 3.2 n A at a bias point around ? /e(where e is half the energy gap of an STJ),and a high fabrication yield of 87%. Although the I leak values are slightly larger than those of STJs produced using the conventional O2 oxidation process, the STJ produced using O3 oxidation shows a ?E = 10 eV for the C-Kα line, which is the best value of our Nb/Al STJ x-ray detectors.     

A Base-Emitter Self-Aligned Multi-Finger Sil-xGex/Si Power Heterojunction Bipolar Transistor

With a crystal orientation dependent on the etch rate of Si in KOH-based solution, a base-emitter self-Migned large-area multi-finger configuration power SiGe heterojunction bipolar transistor （HBT） device （with an emitter area of about 880μm^2） is fabricated with 2μm double-mesa technology. The maximum dc current gain is 226.1. The collector-emitter junction breakdown voltage BVcEo is 10 V and the collector-base junction breakdown voltage BVcBo is 16 V with collector doping concentration of 1 × 10^17 cm^-3 and thickness of 400nm. The device exhibited a maximum oscillation frequency fmax of 35.5 GHz and a cut-off frequency fT of 24.9 GHz at a dc bias point of Ic = 70 mA and the voltage between collector and emitter is VCE = 3 V. Load pull measurements in class-A operation of the SiGe HBT are performed at 1.9 GHz with input power ranging from OdBm to 21 dBm. A maximum output power of 29.9dBm （about 977mW） is obtained at an input power of 18.SdBm with a gain of 11.47dB. Compared to a non-self-aligned SiGe HBT with the same heterostructure and process, fmax and fT are improved by about 83.9% and 38.3%, respectively.     

Zeeman spectroscopy of the 4 Eu → 2 B 1g phosphorescence of copper porphin in an n-alkane single crystal

The phosphorescence spectrum of the metastable ⁴ E_u state of copper porphin in single crystals of n-octane (C₈) and n-decane (C₁₀) has been studied between 2·3 and 35 K, with and without a magnetic field B. The crystal field splitting between the orbital components observed at 35 K is δ = 30·3 ± 0·3 (C₈), 13·8 ± 0·2 cm^-1 (C₁₀). From the Zeeman shifts we derive the effective orbital angular momentum Λ′ = 0·8 ± 0·2 (C₁₀), the spin-orbit coupling parameter |Z′| = 1·5 ± 1·0 cm^-1 (C₁₀), the spin-spin dipolar interaction parameters D = -0·1 ± 0·2 cm^-1 (C₈, C₁₀) and |E| = 0·31 ± 0·03 cm^-1 (C₈, C₁₀), and the g-factors g _∥ = 2·14 ± 0·04 (C₈, C₁₀) and g _⊥ = 2·00 ± 0·03 (C₈, C₁₀).     

The ground-state rotational constants of silane

From thirty-nine combination difference equations we have determined three significant ground-vibronic state constants of silane: β ⁰/hc=2·85941 cm^-1, γ ⁰/hc=-3·82×10^-5 cm^-1 and ε ⁰/hc=-7·97×10^-7 cm^-1 or in Hecht's notation B ₀=2·85941 cm^-1, D _s=3·82×10^-5 cm^-1 and D _t=2·436×10^-6 cm^-1.     

A high resolution FTIR spectroscopic study of the hydrogen-bonded heterodimer H3N−HCN

The spectrum of the symmetric top, hydrogen-bonded heterodimer H₃N?HCN has been recorded between 2900 and 3200cm^?1 using a high resolution FTIR spectrometer. The more intense bands are associated with the ν₂ (H?CN stretch) vibration and include hot bands associated with the low frequency modes ν₅, ν₂ and ν₁₀. Weaker difference bands of the type ν₂+(n?1) ν5?nν₅ are also observed. Analysis of the bands yields values for the band origins: ν2/0=3110·5±0·2cm^?1 and ν5/0=140±5cm^?1 and the anharmonicity constants: x _2,10=12·7±0·5cm^?1, x _2,9≈x _2,5=23±3cm^?1 and x _5,10=?5±2cm^?1. The lifetime in ν₂ with respect to vibrational predissociation, estimated from the width of the sharpest observed feature, is 100?200 ps but there is some indication that this lifetime may decrease at high J.     

Anharmonic force constants of GaSb from the measured third order elastic constants at 300°K

The third-order elastic constants of single crystal GaSb are determined using ultrasonic pulse interferometer at 10 MHz. The constants at 300°K, in units of 10¹¹ N.m.⁻², are C_l11 = ™ 4 ·75 ± 0·06 C₁₄₄ = + 0·50 ± 0·25 C₁₁₃ = ™ 3 ·08 ± 0·02 C₁₆₆ = ™ 2·16 ± 0·13 C₁₂₃ = ™ 0 ·44 ± 0·29 C₄₅₆ = ™ 0·25 ± 0·15 These constants are used to evaluate the three anharmonic first and second neighbour force constants based on modified Keating’s model. The constants are (in units of 10¹¹ N.m⁻²)γ=− 2·406;δ=0·407;ε=−0·222.     

High-resolution infrared spectrum of acetylene in the region of the bending fundamental v 5

The infrared spectrum of C₂H₂ in the region of the bending fundamental v ₅ has been studied at a resolution of about 0·015 cm^-1. The molecular constants G ₀(v ₅=1) = 730·3341 (1) cm^-1 and B ₀ = 1·176641 (2) cm^-1 have been derived. In addition to the fundamental, all the hot bands starting from the levels v ₄ and v ₅ have been investigated. The vibrational, vibration-rotation coupling and centrifugal constants for the excited vibrational states v ₅ = 2 and v ₄ = v ₅ = 1 have been derived using the vibration-rotation energy matrix.     

E.S.R. and ENDOR of an α-chloro radical in X-irradiated 5-chlorodeoxyuridine single crystals

The most prominent radical formed from X-irradiation of the nucleic acid constituent analogue 5-chlorodeoxyuridine at room temperature is shown to be an α-chloro radical formed by hydrogen addition to C₆. The E.S.R. analysis of the ³⁵Cl hyperfine interaction combined with theoretical simulation of the spin hamiltonian yields tensor components a_xx =46·98 MHz, a_yy =-10·98 MHz and a_zz =-17·01 MHz with a quadrupole coupling constant of eqQ=72 MHz. The principal g-tensor values are g_xx =2·0012, g_yy =2·00862 and g_zz =2·00687. Three additional hyperfine interactions in the radical are observed combining E.S.R. and ENDOR spectroscopy. Besides the two nearly equivalent β-protons on C₆ with principal values of 103·39 MHz and 110·12 MHz, there is hyperfine interaction with the ¹⁴N nucleus of nitrogen N₃ (a_xx =9·81 MHz, a_yy =a_zz ? 0 MHz) and with the proton of the hydrogen bonded to N₃. The latter interaction has tensor components of 2·65 MHz, -10·80 MHz and -8·09 MHz as obtained from ENDOR data. The chlorine hyperfine coupling parameters are related to those observed in other α-chloro radicals. The mechanism of the formation of the radical in 5-chlorodeoxyuridine is discussed briefly.     

A new molecular C60 complex with bis(methylenedithio)tetrathiafulvalene (BMDT-TTF): Synthesis, crystal structure, and properties

A new molecular C₆₀ complex of the composition (BMDT-TTF) · C₆₀ · 2CS₂ (I) with the bis(methylenedithio)tetrathiafulvalene (BMDT-TTF) organic donor is synthesized. The molecular and crystal structures of this complex are determined by x-ray diffraction. The (BMDT-TTF) · C₆₀ · 2CS₂ (I) compound crystallizes in a monoclinic crystal system. The main crystal data are as follows: a=13.550(5) Å, b=9.964(7) Å, c=17.125(8) Å, β=99.52(4)°, V=2280(2) ų, M=1229.45, and space group P2₁/m. Crystals of I have a layered structure: layers consisting of C₆₀ molecules alternate with layers composed of BMDT-TTF and CS₂ molecules. It is found that, in complex I, the donor and C₆₀ molecules are linked through the shortest contacts, which leads to a change in the molecular geometry of BMDT-TTF. The donor molecules in a crystal layer are characterized by the shortest S...S contacts. The IR data indicate the electroneutrality of the fullerene molecule. The electrical conductivity of (BMDT-TTF) · C₆₀ · 2CS₂ single crystals is measured using the four-point probe method at room temperature: σ_RT=2×10^?5 Ω^?1 cm^?1.     

EPR study of Fe3+ and Mn2+ in CeO2 and ThO2

Attempts were made to grow CeO₂ and ThO₂ single crystals doped with transition metal ions. Only Fe³⁺ and Mn²⁺ could be detected by the EPR technique. The EPR spectrum of Fe³⁺ in CeO₂ exhibits the well-known fine structure in cubic fields. The parameters areg=2.0044(1) anda=15.6(1)·10^?4 cm^?1. The hyperfine constantA for⁵⁷Fe in hexahedral coordination was found to be 8.9(1)·10^?4 cm^?1. The EPR spectrum of Mn²⁺ in CeO₂ reveals two cubic Mn²⁺ centers. The parameters for center 1 areg=1.9999(1) andA=86.9(1)·10^?4 cm^?1 and for center 2g=1.9984(1) andA=87.0(1)·10^?4 cm^?1. Heating the Mn doped CeO₂ samples in hydrogen, the Mn²⁺ centers transform from cubic into trigonal centers with approximate values ofg=1.9988(2),A=84.5(6)·10^?4 cm^?1 andD=203(1)·10^?4 cm^?1. The two observed Mn²⁺ centers in ThO₂ exhibita priori axial symmetry with approximate values ofg=2.0006(2),A=88.9(4)·10^?4 cm^?1 andD=33(3)·10^?4 cm^?1.     

Crystal structure of N-m-tolyl phthalimide

N-m-tolyl phthalimide, C₁₅NO₂H₁₁ crystallizes in the space group Cc with unit cell dimensions,a=8·54(1),b=19·89(2),c = 7·59(1)A, β=114·53(1)° andZ=4.V=1173(2)A³,D _m =1·35(1),D _c = 1·344 mg.m⁻³,M _r =237 λCoK_a=1·7903A. The structure was solved byMULTAN and refined to an R-factor of 0·116 for 632 counter reflections. The molecules are held together by van der Waal’s forces. The angle between the tolyl plane and the plane through the phthalimide group is 53·4(4)°. Contribution No. 607.