Influence of oxygen concentration on optical properties of semi-insulating polycrystalline silicon films

Optical properties of semi-insulating polycrystalline silicon (SIPOS) films were investigated over the wide region of wavelengths. The vibrational modes of Si-O-Si and Si-Si bonds were studied by IR and Raman spectroscopy. A pronounced effect of oxygen content on the measured spectra was observed. Optical constants of SIPOS films have been compared with those of amorphous silicon and glassy silicon dioxide and their values have been successfully interpreted in terms of the theory of effective medium. The results have shown that the amorphous character prevails in the as-deposited SIPOS films.     

具有半绝缘多晶硅完全三维超结横向功率器件

为了突破传统LDMOS (lateral double-diffused MOSFET)器件击穿电压与比导通电阻的硅极限的2.5 次方关系, 降低LDMOS器件的功率损耗, 提高功率集成电路的功率驱动能力, 提出了一种具有半绝缘多晶硅SIPOS (semi-insulating poly silicon)覆盖的完全3 D-RESURF (three-dimensional reduced surface field)新型Super Junction-LDMOS结构(SIPOS SJ-LDMOS). 这种结构利用SIPOS的电场调制作用使SJ-LDMOS的表面电场分布均匀, 将器件单位长度的耐压量提高到19.4 V/μupm; 覆盖于漂移区表面的SIPOS使SJ-LDMOS沿三维方向均受到电场调制, 实现了LDMOS的完全3 D-RESURF效应, 使更高浓度的漂移区完全耗尽而达到高的击穿电压; 当器件开态工作时, 覆盖于薄场氧化层表面的SIPOS的电场作用使SJ-LDMOS的漂移区表面形成多数载流子积累, 器件比导通电阻降低. 利用器件仿真软件ISE分析获得, 当SIPOS SJ-LDMOS的击穿电压为388 V时, 比导通电阻为20.87 mΩ·cm², 相同结构参数条件下, N-buffer SJ-LDMOS的击穿电压为287 V, 比导通电阻为31.14 mΩ·cm²; 一般SJ-LDMOS 的击穿电压仅为180 V, 比导通电阻为71.82 mΩ·cm².     

Electronic properties of Semi-Insulating Polycrystalline-Silicon (SIPOS) doped with oxygen atoms

The temperature dependence of the electrical conductivity of SIPOS shows that there are two kinds of conduction mechanisms, conduction in extended states and hopping conduction through localized states dominant above and below room temperature, respectively. The change in the conductance of a SIPOS film due to a transverse electric field can well be understood by the CFO model of amorphous semiconductors and indicates that the Fermi level in the thermal equilibrium is near the midgap, and the results show the density of localized states at the Fermi level to be about 10²⁰ cm^?3 eV^?1.     

Erbium doping of crystalline and amorphous silicon for optoelectronic applications

Summary In this work we demonstrate that efficient light emission at 1.54 μm can be achieved when Er ions are incorporated into crystalline Si or in heavily oxygen-doped amorphous and polycrystalline Si films (SIPOS). We have found that temperature quenching of photo- and electroluminescence, which is the major limitation towards the achievement of room temperature luminescence, can be strongly reduced by codoping these films with oxygen. This impurity is already present in as-prepared SIPOS and it is introduced by ion-implantation in crystalline Si. Er luminescence is obtained under both optical and electrical excitation and we demonstrate that excitation occurs through a carrier-mediated process. Electrical excitation is obtained by incorporating Er in properly designed device structures. It is found that this excitation can occur both through the recombination of hole-electron pairs and through impact excitation of the Er ions by hot electrons. These two mechanisms have different efficiencies and impact excitation is shown to prevail at room temperature. These data are presented and possible future developments are discussed. Paper presented at the III INSEL (Incontro Nazionale sul Silicio Emettitore di Luce), Torino, 12–13 October 1995.     

Optical properties of TlGaxIn1-xSe2-layered mixed crystals (0.5 ≤ x ≤ 1) by spectroscopic ellipsometry,transmission, and reflection measurements

The layered semiconducting TlGa_xIn_1-xSe₂-mixed crystals (0.5?≤?x?≤?1) were studied for the first time by spectroscopic ellipsometry measurements in the 1.2–6.2?eV spectral range at room temperature. The spectral dependence of the components of the complex dielectric function, refractive index, and extinction coefficient were revealed using an optical model. The interband transition energies in the studied samples were found from the analysis of the second-energy derivative spectra of the complex dielectric function. The effect of the isomorphic cation substitution (indium for gallium) on critical point energies in TlGa_xIn_1-xSe₂ crystals was established. Moreover, the absorption edge of TlGa_xIn_1-xSe₂ crystals have been studied through the transmission and reflection measurements in the wavelength range of 500–1100?nm. The analysis of absorption data revealed the presence of both optical indirect and direct transitions. It was found that the energy band gaps decrease with the increase of indium content in the studied crystals.     

Studying the Concentration Dependences of IR Spectra for Aqueous Solutions of Alkali Metal Chlorides at a Negative Temperature

In this work, the concentration dependences of IR spectra were studied for aqueous LiCl, NaCl, RbCl, and CsCl solutions within the range from 4 to 0.2 M and an aqueous KCl solution within the range from 3 to 0.2 M at a temperature of –3.5°C in the middle IR region. The wavenumbers of the absorption band maxima were determined for stretching (ν₁, ν₃), combined (ν₂ + ν_L), and bending ν₂ vibrations at these concentrations. The established trends of the shift in the considered absorption bands provided a basis to make several conclusions about the structural transformations of the studied solutions with a decrease in concentration within the studied range. The calculations demonstrated an increase in the energy of hydrogen bonds between water molecules and their reduction in length with decreasing concentration for all of the studied solutions.     

Wigner and Weyl functions for <Emphasis Type="Italic">p</Emphasis>-adic quantum mechanics

A quantum system with positions in Z_p and momenta in Q_p/Z_p is studied. The displacement operators and also the displaced parity operators in the Z_p × Q_p/Z_p phase space of this system, are studied. The Weyl functions (which are intimately related to the displacement operators) and the Wigner functions (which are intimately related to the displaced parity operators) are discussed.     

On the Urbach rule in sulphur-implanted Cu6PS5I superionic conductors

Cu₆PS₅I superionic crystals, grown using chemical vapour transport, were implanted by sulphur ions. The ion implantation effect on the phase transitions is studied by temperature isoabsorption investigation of the optical absorption edge. For the implanted crystals the optical absorption edge shape is studied in the temperature range 77-320 K, the parameters of exciton-phonon interaction, resulting in the Urbach behaviour of the optical absorption edge, are determined, the temperature dependences of the optical pseudogap and Urbach energy are obtained. The implantation effect on the ordering-disordering processes in Cu₆PS₅I superionic conductors is studied.     

Crystalline structure of a C60/C70 membrane

The crystalline structure of a C₆₀/C₇₀ membrane prepared by an original technique has been studied by x-ray diffraction and Raman spectroscopy. The effects of purification of the starting C₆₀/C₇₀ mixture to C₇₀ composition and of spatial separation of the C₆₀ and C₇₀ phases in the membrane have been revealed. The samples studied were established to have a composition gradient from C₆₀ to C₇₀. The main structure of the membrane is shown to be an fcc lattice with a=14.308 Å.     

Temperature dependence of the critical current of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−δ</Subscript> films

The temperature dependence of the critical current of YBa₂Cu₃O_7?δ films is studied experimentally. The performed analysis allows separating two components of the critical current owing to pinning of vortices both on defects in the volume of the superconductor and on oxygen vacancies in the CuO₂ planes. The established temperature dependences of components make it possible to correctly describe the behavior of the total critical current in the studied temperature range from 4.2 K to the irreversibility temperature.     

Interesting normal state and superconducting properties of the intermediate valence compound CeRu2

Superconductivity in CeRu₂ was discovered 40 years ago, and was extensively studied because alloying with magnetic elements showed the coexistence of superconductivity and magnetic order. The normal state of CeRu₂ has been of interest because of its intermediate valuence character. The superconducting state has been studied extensively because of its paramagnetic nature and anomalous pinning properties. This review presents the present status of knowledge, and discusses the puzzling features of CeRu₂.     

Role of exciton-phonon interactions and disordering processes in the formation of the absorption edge in Cu<Subscript>6</Subscript>P(S<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>x</Subscript>)<Subscript>5</Subscript>Br crystals

The absorption edge in Cu₆P(S_1?x Se_x)⁵Br crystals has been studied for strong absorption in the temperature range of 77–330 K. The parameters of the Urbach absorption edge and exciton-phonon interactions in Cu₆P(S_1-x Se_x)₅Br crystals are determined and their effect on the composition disorder is studied.     

Thermally stimulated luminescence studies of undoped,Cu- and Mn-doped CaSO4 compounds

Thermally stimulated luminescence (TSL) of undoped and doped CaSO₄ with activators such as Cu and Mn has been investigated. The polycrystalline samples of undoped and doped CaSO₄ are prepared by the melting method. The formation of CaSO₄ compound is confirmed by X-ray diffraction and Fourier transform infrared studies. Scanning electron microscopic studies of CaSO₄ are also carried out.

The TSL glow curves of undoped CaSO₄, Cu- and Mn-doped CaSO₄ are studied. Comparison of the thermoluminescence (TL) intensity of the most intensive glow peak of Cu-doped CaSO₄ compound with that of undoped CaSO₄ shows that addition of Cu impurity in CaSO₄ compound enhances the TL intensity by about four times. However, the addition of Mn impurity to undoped CaSO₄ increases the TL intensity by about three times when compared with that of undoped CaSO₄. The TL-dose dependence of all three samples was studied and was observed to be almost linear in the studied range of irradiation time. Among the samples studied, namely undoped CaSO₄ and Cu- and Mn-doped CaSO₄, Cu-doped CaSO₄ is found to be the most sensitive. The trap parameters, namely order of kinetics (b), activation energy (E) and frequency factor (s) associated with the most intensive glow peaks of CaSO₄:Mn, CaSO₄:Cu and CaSO₄ phosphors were determined using the glow curve shape (Chen's) method.     

Phase composition and properties of superconducting ceramics based on Bi1.7Pb0.3Sr2Ca2Cu3Oy precursors fabricated by melt quenching in a solar furnace

Production of superconducting ceramics based on precursors with rated composition Bi_1.7Pb_0.3Sr₂Ca₂Cu₃O _y is studied. The precursors are synthesized in a solar furnace by melt rapid quenching. The phase composition of the samples is examined by microstructural and X-ray analyses. The temperature dependences of the resistance and magnetic susceptibility are measured. The influence of the composition and crystal structure of the substrate on texturing in the Bi-Sr-Ca-Cu-O system is studied. It is found that the type of quenching plays a significant role, while the type of substrate is of minor significance.     

Magnetic properties of the ternary hydrides of Nd6Mn23 and Sm6Mn23

The intermetallic compounds Nd₆Mn₂₃ and Sm₆Mn₂₃ and their ternary hydrides were studied by X-ray diffraction. The crystal structure (Th₆Mn₂₃ type) is preserved after hydrogen absorption. From the change in lattice constants a volume increase of about 14% was deduced. The temperature dependence of the magnetization of Nd₆Mn₂₃, Sm₆Mn₂₃ and their hydrides was studied in the range 4–500 K. The uncharged compounds have magnetic ordering temperatures above 400 K while in the hydrides magnetic ordering occurs close to 200 K. Indications were obtained of a substantial weakening of the magnetic coupling between the rare earth and manganese sublattice magnetization.     

Soot-visualization strategies using laser techniques

Strategies for spatially resolved soot volume-fraction measurements have been investigated in sooting laboratory flames with known soot characteristics. Two techniques were compared: Laser-Induced Fluorescence in C₂ from Laser-Vaporized Soot (LIF(C₂)LVS), and Laser-Induced Incandescence of soot (LII). The LII signal is the increased temperature radiation from soot particles which have been heated to temperatures of several thousand degrees as a consequence of absorption of laser radiation. The LIF(C₂)LVS technique is based on the production of C₂ radicals from laser-vaporized soot which occurs for laser intensities ≥10⁷ W/cm². A laser wavelength is chosen such that besides vaporizizng the soot, it also excites the C₂ radicals, and the subsequent C₂ fluorescence signal is detected. The signals from both techniques showed good correlation with soot volume fractions in the studied flame. The dependence of the signals on experimental parameters was studied, and the influence of interfering radiation, such as background flame luminosity and fluorescence from polyaromatic hydrocarbons, on studied signals was established. The potential of the two techniques for imaging of soot volume fractions in laboratory flames was demonstrated. Advantages and disadvantages of the studied techniques are discussed.     

Optical properties of chalcogenide glasses in the terahertz spectral region

Optical properties of chalcogenide glasses of three different compositions (As₂S₃, As₂S₃ × As₂Se₃, and As₂Se₃) are studied via terahertz pulsed spectroscopy. Absorption coefficients and refractive indices are measured in a frequency range of 0.2–1.6 THz. The results show that the phonon modes of the studied materials vary with the composition of the glasses.     

The anodization of ZK60 magnesium alloy in alkaline solution containing silicate and the corrosion properties of the anodized films

The anodization of ZK60 magnesium alloy in an alkaline electrolyte of 100 g/l NaOH + 20 g/l Na₂B₄O₇·10H₂O + 50 g/l C₆H₅Na₃O₇·2H₂O + 60g/l Na₂SiO₃·9H₂O was studied in this paper. The corrosion resistance of the anodic films was studied by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques and the microstructure and composition of films were examined by SEM and XRD. The influence of anodizing time was studied and the results show that the anodizing time of 60 min is suitable for acquiring films with good corrosion resistance. The influence of current density on the corrosion resistance of anodizing films was also studied and the results show that the film anodized at 20 mA/cm² has the optimum corrosion resistance. The film formed by anodizing in the alkaline solution with optimized parameters show superior corrosion resistance than that formed by the traditional HAE process. The XRD pattern shows that the components of the anodized film consist of MgO and Mg₂SiO₄.     

Dissociative excitation of the singly charged manganese ion in collisions of electrons with manganese diiodide molecules

The dissociative excitation of the singly charged manganese ion in collisions of electrons with MnI₂ molecules is experimentally studied. At exciting electron energy of 100 eV, 16 dissociative excitation cross sections were measured. The studied transitions occur within the quintet and septet term systems in the absence of intercombination transitions. The measured values of the cross sections are compared to similar values obtained previously in studies of e–MnCl₂ and e–MnBr₂ collisions.     

IR multiphoton absorption of SF6 in flow with Ar at moderate energy fluences

6 in flow with Ar (SF₆: Ar=1:100) in conditions of a large vibrational/rotational temperature difference (T_V≃230 K, T_R≃60 K) was studied at moderate energy fluences from ≃0.1 to ≃100 mJ/cm², which are of interest for isotope selective two-step dissociation of molecules. A 50 cm Laval-type slit nozzle for the flow cooling, and a TEA CO₂-laser for excitation of molecules were used in the experiments. The laser energy fluence dependences of the SF₆ MPA were studied for several CO₂-laser lines which are in a good resonance with the linear absorption spectrum of the ν₃ vibration of SF₆ at low temperature. The effect of the laser pulse duration (intensity) on MPA of flow cooled SF₆ with Ar was also studied. The results are compared with those obtained in earlier studies. Received: 4 September 1995/Revised version: 15 February 1996