Effect of cobalt substitution on the optical properties of bismuth ferrite thin films

Effect of cobalt substitution on the band gap and absorption coefficient of the BiFeO₃ thin films formed on quartz substrate by low cost spin coating method have been investigated. BiFe_1−xCo_xO₃ (x=0, 0.03, 0.06 and 0.10) thin films are polycrystalline and it retains the rhombohedral distorted perovskite structure up to 10 mole % of Co substitution. Smooth and compact surface morphology with uniform size particles are observed in SEM micrographs. Narrowing and broadening of band gap is observed as a function of Co content. Two strong emission peaks at ~2.51 eV and ~2.38 eV are recorded for all films with noticeable change in intensity. Results obtained from the optical absorption and photoluminescence spectroscopy experiments have shown that there exists an inverse correlation between the variation in the band gap and the concentration of oxygen vacancies. Band gap decreased by ~100 meV and absorption coefficient increased by 28% at the wavelength of 375 nm in 6 mole % Co substituted thin film and these observations are necessary requirements to improve the efficiency of photovoltaic devices.     

Distributed phase shifter with pyrochlore bismuth zinc niobate thin films

A monolithic Ku-band phase shifter employing voltage tunable Bi/sub 1.5/Zn/sub 1.0/Nb/sub 1.5/O/sub 7/ (BZN) thin film parallel plate capacitors is reported. BZN films were deposited by radio frequency magnetron sputtering on single-crystal sapphire substrates. A nine-section distributed coplanar waveguide loaded-line phase-shifter structure was designed. A differential phase shift of 175/spl deg/ was achieved with a maximum insertion loss of 3.5 dB at 15 GHz, giving a figure of merit /spl sim/50/spl deg//dB. To the best of our knowledge, this is the first demonstration of a monolithic tunable microwave circuit using BZN thin films.     

Physical properties of sprayed antimony doped tin oxide thin films: Role of thickness

Transparent conducting antimony doped tin oxide (Sb:SnO₂) thin films have been deposited onto preheated glass substrates using a spray pyrolysis technique by varying the quantity of spraying solution. The structural, morphological, X-ray photoelectron spectroscopy, optical, photoluminescence and electrical properties of these films have been studied. It is found that the films are polycrystalline in nature with a tetragonal crystal structure having orientation along the (211) and (112) planes. Polyhedrons like grains appear in the FE-SEM images. The average grain size increases with increasing spraying quantity. The compositional analysis and electronic behaviour of Sb:SnO₂ thin films were studied using X-ray photoelectron spectroscopy. The binding energy of Sn3d_5/2 for all samples shows the Sn⁴ bonding state from SnO₂. An intensive violet luminescence peak near 395 nm is observed at room temperature due to oxygen vacancies or donor levels formed by Sb⁵ ions. The film deposited with 20 cc solution shows 70% transmittance at 550 nm leading to the highest figure of merit (2.11 × 10^-3 Ω^-1). The resistivity and carrier concentration vary over 1.22 × 10^-3 to 0.89 × 10^-3Ωcm and 5.19 × 10²⁰ to 8.52 × 10²⁰ cm^-3, respectively.     

Physical properties of sprayed antimony doped tin oxide thin films:The role of thickness

Transparent conducting antimony doped tin oxide（Sb:SnO₂） thin films have been deposited onto preheated glass substrates using a spray pyrolysis technique by varying the quantity of spraying solution.The structural, morphological,X-ray photoelectron spectroscopy,optical,photoluminescence and electrical properties of these films have been studied.It is found that the films are polycrystalline in nature with a tetragonal crystal structure having orientation along the（211） and（112） planes.Polyhedrons like grains appear in the FE-SEM images. The average grain size increases with increasing spraying quantity.The compositional analysis and electronic behaviour of Sb:SnO₂ thin films were studied using X-ray photoelectron spectroscopy.The binding energy of Sn3d_5/2 for all samples shows the Sn⁴⁺ bonding state from SnO₂.An intensive violet luminescence peak near 395 nm is observed at room temperature due to oxygen vacancies or donor levels formed by Sb⁵⁺ ions.The film deposited with 20 cc solution shows 70%transmittance at 550 nm leading to the highest figure of merit(2.11×10^-3Ω^-1). The resistivity and carrier concentration vary over 1.22×10^-3 to 0.89×10^-3Ω·cm and 5.19×10²⁰ to 8.52×10²⁰ cm^-3,respectively.     

硒化锑薄膜光伏性能调控研究进展

硒化锑太阳能电池具有较高的理论转换率,是近年来颇受关注的太阳能电池之一。人们在研究过程中发现硒化锑薄膜性能受到多重因素影响。本文从退火工艺、组成和微结构等方面阐述关于它们对硒化锑薄膜光伏性能的影响的最新研究进展,并分析原因,提出了增强硒化锑薄膜光伏效应的建议及研究方向。     

Influence of bismuth on the optical properties of Ge2Sb2Te5 thin films

Chalcogenide alloys in the Ge-Sb-Te system are promising for application in phase-change memory devices. We investigated the influence of bismuth on the optical properties of Ge₂Sb₂Te₅ thin films and established that the bismuth doping in them allows the optical contrast of the thin films to be increased by about 30% at a wavelength of 400 nm. The experimental results are explained in an assumption on the impurity substitution of bismuth for antimony.     

Numerical prediction of mechanical properties of Pb-Sn solder alloys containing antimony, bismuth and or silver ternary trace elements

Solder joint interconnects are mechanical means of structural support for bridging the various electronic components and providing electrical contacts and a thermal path for heat dissipation. The functionality of the electronic device often relies on the structural integrity of the solder. The dimensional stability of solder joints is numerically predicted based on their mechanical properties. Algorithms to model the kinetics of dissolution and subsequent growth of intermetallic from the complete knowledge of a single history of time-temperature-reflow profile, by considering equivalent isothermal time intervals, have been developed. The information for dissolution is derived during the heating cycle of reflow and for the growth process from cooling curve of reflow profile. A simple and quick analysis tool to derive tensile stress-strain maps as a function of the reflow temperature of solder and strain rate has been developed by numerical program. The tensile properties are used in modeling thermal strain, thermal fatigue and to predict the overall fatigue life of solder joints. The numerical analysis of the tensile properties as affected by their composition and rate of testing, has been compiled in this paper. A numerical model using constitutive equation has been developed to evaluate the interfacial fatigue crack growth rate. The model can assess the effect of cooling rate, which depends on the level of strain energy release rate. Increasing cooling rate from normalizing to water-quenching, enhanced the fatigue resistance to interfacial crack growth by up to 50% at low strain energy release rate. The increased cooling rates enhanced the fatigue crack growth resistance by surface roughening at the interface of solder joint. This paper highlights salient features of process modeling. Interfacial intermetallic microstructure is affected by cooling rate and thereby affects the mechanical properties.     

Thick films or thin?

It is sometimes difficult to decide between thick-film and thin-film technologies in the fabrication of hybrid integrated circuits consisting of a ceramic substrate with deposited passive components and attached active devices. In the case of thick films, the deposited pattern of conductors, resistors, capacitors, and inductors is applied to the substrate by screen-printing and firing special conductive, resistive, or dielectric pastes. Thin-film layers, on the other hand, are deposited in vacuum by evaporation or cathode-sputtering of appropriate source materials. This article discusses the advantages and disadvantages of both technologies as well as their application ranges.     

Effect of doping concentration on the properties of bismuth doped tin sulfide thin films prepared by spray pyrolysis

Bismuth doped tin sulfide (SnS:Bi) thin films were deposited onto glass substrates by the spray pyrolysis technique at the substrate temperature of 350 °C. The effect of doping concentration [Bi/Sn] on their structural, optical and electrical properties was investigated as a function of bismuth doping between 0 and 8 at%. The XRD results showed that the films were polycrystalline SnS with orthorhombic structure and the crystallites in the films were oriented along (111) direction. Atomic force microscopy revealed that the particle size and surface roughness of the films increased due to Bi-doping. Optical analysis exhibited the band gap value of 1.40 eV for SnS:Bi (6 at%) which was lower than the band gap value for 0 at% of Bi (1.60 eV). The film has low resistivity of 4.788×10⁻¹ Ω-cm and higher carrier concentration of 3.625×10¹⁸ cm⁻³ was obtained at a doping ratio of 6 at%.     

Properties of antimony doped ZnO thin films deposited by spray pyrolysis technique

Antimony (Sb) doped zinc oxide (ZnO) thin films were deposited on the glass substrate at 450°C using spray pyrolysis technique. Effect of Sb doping on surface morphology structural, optical and electrical properties were studied. X-ray diffraction (XRD) analysis showed that both the undoped and doped ZnO thin films are polycrystalline in nature with (101) preferred orientation. SEM analysis showed a change in surface morphology of Sb doped ZnO thin films. Doping results in a marked increase in conductivity without affecting the transmittance of the films. ZnO films prepared with 3 at % Sb shows the lowest resistivity of 0.185 Ohm cm with a Hall mobility of 54.05 cm² V^–1 s^–1, and a hole concentration of 6.25 × 10¹⁷ cm^–3.     

Optical properties of PbS thin films

The complex dielectric function of PbS thin films is studied by spectroscopic ellipsometry in the spectral range from 0.74 to 6.45 eV at a temperature of 293 K. The critical energies are determined to be E ₁ = 3.53 eV and E ₂ = 4.57 eV. For both energy regions, the best fit is attained at the critical point 2D (m = 0). In addition, the Raman spectra and the optical-absorption spectra of PbS thin films are studied. From the dependence of the quantity (αhν)² on the photon energy hν, the band gap is established at E _g = 0.37 eV.     

Optoelectronic properties of ZnSe thin films

ZnSe/Si Schottky diodes were fabricated by the vacuum evaporation technique at different substrate temperatures (303 and 483 K) and the results are discussed. Compositions of the deposited films were measured by Rutherford backscattering analysis. The atomic percentages of Zn and Se were evaluated as 0.50 and 0.50, respectively. Structural analysis shows that deposited films posses good crystalline nature with a cubic structure oriented along the (1 1 1) direction. In the Raman analysis, the presence of the LO mode confirms that the deposited films have the crystalline nature. Photoconduction analyses were performed on the prepared device. The prepared device exhibits a strong photoresponse in the visible region.     

半导体氮化物AlInN的光学性质

测量了AlInN薄膜(包括InN和AIN)的透射和反射光谱,结合四层透射和反射模型得到AlInN的一系列变温光学性质,包括吸收系数、能带带隙、乌尔巴赫带尾参数、折射率等等.采用一套经验公式,描述InN薄膜在本征吸收区和乌尔巴赫吸收区的吸收系数.发现带隙以下,AIN薄膜的折射率遵守Sellmeier经验公式.用基于态密度...     

Electrical properties of tellurium thin films

Semiconducting properties of evaporated tellurium thin films, in the thickness range of 100 to 400 Å, are studied and correlated with observed structural properties. It is found that less-than-monolayer gold films can act as nucleation sites and stimulate the growth of large crystallites in deposited Te films. The Au-nucleated Te films are preferentially oriented with the c axis in the substrate plane and have crystallite diameters ranging from 2 to 5 µm. Hall mobilities as high as 250 cm²/V ċ s are observed in 400-Å Au-nucleated films with 5-µm crystallites. These large-grain films exhibit a temperature dependence for mobility of the form µ ∼ T^3/2between 85°K and 250°K, while the carrier concentrations in the films do not change appreciably with temperature. Transconductances greater than 1000 µmhos are achieved for Au-nucleated Te thin-film transistors with 3-mil channels (operating with a saturated drain current of 1 mA). Several devices exhibit field-effect mobilities greater than 100 cm²/V ċ s, a value consistent with the observed Hall mobilities for similar films. Transconductance measurements indicate that Te thin-film transistor (TFT) instabilities result primarily from hole trapping at the Te-insulator interface. It is possible to alter the threshold voltage of Te TFTs by applying a gate bias at room temperature. Improved stability (changes in V0less than 50 mV in 1 h) is observed at 77°K. From the observed changes in threshold, a lower limit of the trapping-state density at the surface is inferred to be 5×10¹²traps/cm². The surface-state density at the Te-SiO interface is estimated to be less than 6×10¹²surface states/cm²ċ eV as determined from capacitance and conductance measurements.     

Optical and electrical properties of nickel oxide thin films synthesized by sol–gel spin coating

Nickel oxide thin films were prepared by the sol–gel technique combined with spin coating onto glass substrates. The as-deposited films were pre-heated at 275 °C for 15 min and then annealed in air at different temperatures. The effects of the annealing temperature on the structural and optical properties of the films are studied. The results show that 600 °C is the optimum annealing temperature for preparation of NiO films with p-type conductivity and high optical transparency. Then, by using these optimized deposition parameters, NiO thin films of various thicknesses were deposited at the same experimental conditions and annealed under different atmospheres. Surface morphology of the films was investigated by atomic force microscopy. The surface morphology of the films varies with the annealing atmosphere. Optical transmission was studied by UV–vis spectrophotometer. The transmittance of films decreased as the thickness of films increased. The electrical resistivity, obtained by four-point probe measurements, was improved when NiO layers were annealed in N₂ atmosphere at 600 °C.     

Oriented colloidal-crystal thin films of polystyrene spheres via spin coating

We developed a simple and inexpensive synthesis of a large-scale close-packed monolayer of polystyrene sphere arrays, which have a variety of applications. The influence of three step spin speeds, spinning time, solution quantity and relative humidity is studied in order to achieve a large area close-packed monolayer.A relatively high surface coverage and uniform monolayer of PS spheres in the range of 85%–90% are achieved by appropriate control of the preparative parameters. Also the effect of the oxygen plasma etching process on the reduction of PS spheres has been studied. We conclude that it can be useful in industrial applications, because of the fabrication speed, surface coverage, control over PS spheres and cost of the process.     

基于非晶态铌酸锌铋薄膜的新型反熔丝器件

本文提出了一种基于非晶态铌酸锌铋（a-BZN）介质材料的新型反熔丝器件并对其性能特征进行了研究。考察了a-BZN反熔丝器件的关态特性,选用从上至下的编程方向对反熔丝器件进行击穿,其击穿电压约为6.56V。获得了a-BZN反熔丝器件的关态电阻,约为1GΩ。表征分析了击穿后的a-BZN反熔丝器件的表面形貌。研究了a-BZN反熔丝器件的编程特性以及编程后的开态特性,结果表明a-BZN反熔丝器件所需编程时间约为0.46ms,编程后其开态电阻约为26.1Ω。对比分析了a-BZN反熔丝器件与结晶态铌酸锌铋（cp-BZN）反熔丝器件和栅氧反熔丝器件在性能特征等方面的差异。     

Thermoelectric properties of n-type Bi-Te thin films with various compositions

Bismuth-telluride-based materials have excellent room-temperature thermoelectric properties. In this study, the composition of Bi-Te thin films deposited by RF-magnetron sputtering was systematically varied across a single wafer. X-ray diffraction, field emission-scanning electron microscopy (FE-SEM, JEOL, JSM-7000F) and energy dispersive X-ray spectroscopy (EDS) were then used to investigate the thermoelectric properties of the Bi-Te films as a function of the Te fraction. The Te content of the films ranged from 38% to 81%, and their microstructure and crystal structure varied depending on the Te content. The Seebeck coefficients of the Bi-Te thin films were in the range −10 to 153 μV/K, and the maximum power factor of the films was 3.7 × 10⁻⁴ W/K² m, without post annealing.