Substrate temperature influenced physical properties of silicon MOS devices with TiO2 gate dielectric

DC reactive magnetron sputtering technique was employed for deposition of titanium dioxide (TiO₂) films. The films were formed on Corning glass and p‐Si (100) substrates by sputtering of titanium target in an oxygen partial pressure of 6×10^?2 Pa and at different substrate temperatures in the range 303 – 673 K. The films formed at 303 K were X‐ray amorphous whereas those deposited at substrate temperatures ≥ 473 K were transformed into polycrystalline nature with anatase phase of TiO₂. Fourier transform infrared spectroscopic studies confirmed the presence of characteristic bonding configuration of TiO₂. The surface morphology of the films was significantly influenced by the substrate temperature. MOS capacitor with Al/TiO₂/p‐Si sandwich structure was fabricated and performed current–voltage and capacitance–voltage characteristics. At an applied gate voltage of 1.5 V, the leakage current density of the device decreased from 1.8 × 10^?6 to 5.4 × 10^?8 A/cm² with the increase of substrate temperature from 303 to 673 K. The electrical conduction in the MOS structure was more predominant with Schottky emission and Fowler‐Nordheim conduction. The dielectric constant (at 1 MHz) of the films increased from 6 to 20 with increase of substrate temperature. The optical band gap of the films increased from 3.50 to 3.56 eV and refractive index from 2.20 to 2.37 with the increase of substrate temperature from 303 to 673 K. Copyright © 2012 John Wiley & Sons, Ltd.     

Interpreting the conductive atomic force microscopy measured inhomogeneous nanoscale surface electrical properties of Al‐doped ZnO films

In this work, conductive atomic force microscopy is used to study the inhomogeneous surface electrical conductivity of Al‐doped ZnO thin films at a nanoscale dimension. To this end, Al‐doped ZnO films were deposited onto the soda lime glass substrates at substrate temperature (T_s) varying from 303 to 673 K in radio frequency magnetron sputtering. The obtained local surface electrical conductivity values are found to be influenced by their bulk electrical resistivity, surface topography and tip geometry. Further, the average (local) surface conductivity from the film surface is found to increase with increasing T_s from 303 to 623 K, beyond which they decrease until 673 K. Copyright © 2016 John Wiley & Sons, Ltd.     

Dielectric properties and I-V characteristics of (Pb<Subscript>0.4</Subscript>Sr<Subscript>0.6</Subscript>)TiO<Subscript>3</Subscript> thin films improved by TiO<Subscript>2</Subscript> buffer layers

A TiO₂ thin buffer layer was introduced between the (Pb_0.4Sr_0.6)TiO₃ (PST) film and the Pt/Ti/SiO₂/Si substrate in an attempt to improve their electrical properties. Both TiO₂ and PST layers were prepared by a chemical solution deposition method. It was found that the TiO₂ buffer layer increased the (100)/(001) preferred orientation of PST and decreased the surface roughness of the films, leading to an enhancement in electrical properties including an increase in dielectric constant and in its tunability by DC voltage, as well as a decrease in dielectric loss and leakage current density. At an optimized thickness of the TiO₂ buffer layer deposited using 0.02 mol/l TiO₂ sol, the 330-nm-thick PST films had a dielectric constant, loss and tunability of 1126, 0.044 and 60.7% at 10 kHz, respectively, while the leakage current density was 1.95 × 10⁻⁶ A/cm² at 100 kV/cm.     

Fabrication of sol–gel derived ZrO2 thin film for HR coatings via rapid thermal annealing process

The properties of sol–gel derived ZrO₂ thin films heated via a novel method of rapid thermal annealing process were studied. We investigated the effects of heat-treatment schedules with different ramp rates on the refractive index and thickness of ZrO₂ thin films as well. By controlling the heating treatment parameter, the refractive index of the ZrO₂ coatings can be adjusted from 1.69 up to 1.9 continuously, which can meet different requirement for high reflectance well. The thickness of crack-free ZrO₂ coatings can be easily controlled by employing different experimental parameters. The result of X-ray diffraction shows that as-deposited film is amorphous, and it remains stable up to the heating temperature of 400 °C. However, it begins to crystallize as the temperature increases further attaining 500 °C. Meanwhile, the surface morphology was evaluated by atomic force microscopy and the result shows that the surface of the ZrO₂ coating is smooth and uniform with root means square of 0.63 nm for the measured area of 5 × 5 μm. As a typical example, ZrO₂ thin films with refractive index of 1.9 are chosen for highly reflective coatings. Nearly full reflective mirror at 1,064 nm was fabricated on fused silica substrate. The laser induced damage thresholds of 22 J/cm² (1,064 nm, 10 ns) and 14.6 J/cm² (1,064 nm, 10 ns) are obtained for ZrO₂ coating and ZrO₂/SiO₂ multilayer coatings respectively.     

The Metallic Zintl Phase Ba3Si4 – Synthesis,Crystal Structure,Chemical Bonding,and Physical Properties

The Zintl phase Ba₃Si₄ has been synthesized from the elements at 1273 K as a single phase. No homogeneity range has been found. The compound decomposes peritectically at 1307(5) K to BaSi₂ and melt. The butterfly‐shaped Si₄⁶⁻ Zintl anion in the crystal structure of Ba₃Si₄ (Pearson symbol tP28, space group P4₂/mnm, a = 8.5233(3) Å, c = 11.8322(6) Å) shows only slightly different Si‐Si bond lengths of d(Si–Si) = 2.4183(6) Å (1×) and 2.4254(3) Å (4×). The compound is diamagnetic with χ ≈ −50 × 10⁻⁶ cm³ mol⁻¹. DC resistivity measurements show a high electrical resistivity (ρ(300 K) ≈ 1.2 × 10⁻³ Ω m) with positive temperature gradient dρ/dT. The temperature dependence of the isotropic signal shift and the spin‐lattice relaxation times in ²⁹Si NMR spectroscopy confirms the metallic behavior. The experimental results are in accordance with the calculated electronic band structure, which indicates a metal with a low density of states at the Fermi level. The electron localization function (ELF) is used for analysis of chemical bonding. The reaction of solid Ba₃Si₄ with gaseous HCl leads to the oxidation of the Si₄⁶⁻ Zintl anion and yields nanoporous silicon.     

Effect of 120 MeV Au9+ ion irradiation on the structure and surface morphology of ZnO/NiO heterojunction

ZnO/NiO thin films, each of thickness 100 nm, were deposited on Si(100) substrate by pulsed laser deposition method. The resulting heterojunction, ZnO/NiO/Si, was irradiated by 120 MeV Au⁹⁺ ions and characterized by grazing incidence X‐ray diffraction (GIXRD), Raman spectroscopy, and atomic force microscopy (AFM). The GIXRD confirmed the presence of both NiO and ZnO in the samples. Ion irradiation induced suppression of crystalline nature, and the recrystallization of the same occurred at the fluence of 1 × 10¹³ ions cm⁻². The occurrence of most intense band at 302 cm⁻¹ in Raman spectra corresponds to the symmetric stretching vibration of ZnO. The linear shift of stretching mode of ZnO with ion fluence could be associated with the effect of compressive stress in the material. AFM analysis of the films indicated that the rms roughness increased when the film is irradiated at a fluence of 1 × 10¹² ions cm⁻². Beyond this fluence, the value of roughness decreased up to fluence of 1 × 10¹³ ions cm⁻² and increased thereafter. To see the effect of the stress of buffer layer on the surface layer, we calculated the stress for NiO layer with ion fluence form the lattice parameter. Comparing the stress of buffer layer with roughness of surface layer at the given fluence, we can say that the compressive stress in the buffer layer could possibly control the roughness of the surface layer.     

Dielectric properties of tetragonal tungsten bronze films deposited by RF magnetron sputtering

Tetragonal tungsten bronze (TTB) films have been synthesised on Pt(111)/TiO₂/SiO₂/Si substrates from Ba₂LnFeNb₄O₁₅ ceramics (Ln = La, Nd, Eu) by RF magnetron sputtering. X-ray diffraction measurements evidenced the multi-oriented nature of films with some degrees of preferential orientation along (111). The dependence of the dielectric properties on temperature and frequency has been investigated. The dielectric properties of the films are similar to those of the bulk, i.e., ε ∼150 and σ ∼10⁻⁶ Ω⁻¹ cm⁻¹ at 1 MHz and room temperature. The films exhibit two dielectric anomalies which are attributed to Maxwell Wagner polarization mechanism and relaxor behaviour. Both anomalies are sensitive to post-annealing under oxygen atmosphere and their activation energies are similar E_a ∼0.30 eV. They are explained in terms of electrically heterogeneous contributions in the films.     

Temperature‐Dependence of the Rates of Reaction of Trifluoroacetic Acid with Criegee Intermediates

The rate coefficients for gas‐phase reaction of trifluoroacetic acid (TFA) with two Criegee intermediates, formaldehyde oxide and acetone oxide, decrease with increasing temperature in the range 240–340 K. The rate coefficients k(CH₂OO + CF₃COOH)=(3.4±0.3)×10⁻¹⁰ cm³ s⁻¹ and k((CH₃)₂COO + CF₃COOH)=(6.1±0.2)×10⁻¹⁰ cm³ s⁻¹ at 294 K exceed estimates for collision‐limited values, suggesting rate enhancement by capture mechanisms because of the large permanent dipole moments of the two reactants. The observed temperature dependence is attributed to competitive stabilization of a pre‐reactive complex. Fits to a model incorporating this complex formation give k [cm³ s⁻¹]=(3.8±2.6)×10⁻¹⁸ T² exp((1620±180)/T) + 2.5×10⁻¹⁰ and k [cm³ s⁻¹]=(4.9±4.1)×10⁻¹⁸ T² exp((1620±230)/T) + 5.2×10⁻¹⁰ for the CH₂OO + CF₃COOH and (CH₃)₂COO + CF₃COOH reactions, respectively. The consequences are explored for removal of TFA from the atmosphere by reaction with biogenic Criegee intermediates.     

Magnetische Suszeptibilität von Calcium,Strontium und Barium zwischen 295 und 3 K

The magnetic susceptibilities of calcium, strontium and barium (purified by fractional sublimation, purity at least 99.9%) have been determined in the temperature range 295-3 K. The samples are free from ferro- and paramagnetic impurities. The data of calcium are temperature independent between 295 and 45 K at 58(2) × 10⁻⁶ cm³ mol⁻¹ and then increase to 63(2) × 10⁻⁶ cm³ mol⁻¹ at 3.3 K. The susceptibility of strontium increases almost linearly from 98(2) × 10⁻⁶ to 136(2) × 10⁻⁶ cm³ mol⁻¹ in the temperature range 295-3.3 K. The data in the case of barium decrease linearly between 295 and 60 K from 31.0(5)× 10⁻⁶ to 25.5(5) × 10⁻⁶ cm³ mol⁻¹ before remaining constant down to 3 K.     

Temperature-Dependence of the Rates of Reaction of Trifluoroacetic Acid with Criegee Intermediates

The rate coefficients for gas-phase reaction of trifluoroacetic acid (TFA) with two Criegee intermediates, formaldehyde oxide and acetone oxide, decrease with increasing temperature in the range 240–340 K. The rate coefficients k(CH₂OO + CF₃COOH)=(3.4±0.3)×10⁻¹⁰ cm³ s⁻¹ and k((CH₃)₂COO + CF₃COOH)=(6.1±0.2)×10⁻¹⁰ cm³ s⁻¹ at 294 K exceed estimates for collision-limited values, suggesting rate enhancement by capture mechanisms because of the large permanent dipole moments of the two reactants. The observed temperature dependence is attributed to competitive stabilization of a pre-reactive complex. Fits to a model incorporating this complex formation give k [cm³ s⁻¹]=(3.8±2.6)×10⁻¹⁸ T² exp((1620±180)/T) + 2.5×10⁻¹⁰ and k [cm³ s⁻¹]=(4.9±4.1)×10⁻¹⁸ T² exp((1620±230)/T) + 5.2×10⁻¹⁰ for the CH₂OO + CF₃COOH and (CH₃)₂COO + CF₃COOH reactions, respectively. The consequences are explored for removal of TFA from the atmosphere by reaction with biogenic Criegee intermediates.     

Growth behavior of Cu/Al intermetallic compounds in hot‐dip aluminized copper

Hot‐dipped aluminum copper with plating auxiliary KF is introduced in this work. In this study, the intermetallic layer thickness varies with dipping temperature and time in a linear relationship. The main phases are identified to be CuAl₂ and K₃AlF₆ by means of X‐ray diffraction. The reaction equations are deduced according to the elements concentration gradient in cross section. The copper diffusion rate in liquid Al is calculated to be 1.13 × 10⁻¹² m²/s by Fick's second law in semi‐infinite solid model, and the obtained conductivity is 1.758–1.767 × 10⁻² Ω mm²/m. The results indicate that the interfacial bonding is in a good state and plating auxiliary KF aqueous solution. can significantly improve the substrate wettability. The appropriate hot‐dipping condition for the samples is 953–973 K for 4–8 s. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of post-deposition annealing temperature on RF-sputtered HfO2 thin film for advanced CMOS technology

Structural and electrical properties of HfO₂ gate-dielectric metal-oxide-semiconductor (MOS) capacitors deposited by sputtering are investigated. The HfO₂ high-k thin films have been deposited on p-type <100> silicon wafer using RF-Magnetron sputtering technique. The Ellipsometric, FTIR and AFM characterizations have been done. The thickness of the as deposited film is measured to be 35.38 nm. Post deposition annealing in N₂ ambient is carried out at 350, 550, 750 °C. The chemical bonding and surface morphology of the film is verified using FTIR and AFM respectively. The structural characterization confirmed that the thin film was free of physical defects and root mean square surface roughness decreased as the annealing temperature increased. The smooth surface HfO₂ thin films were used for Al/HfO₂/p-Si MOS structures fabrication. The fabricated Al/HfO₂/p-Si structure had been used for extracting electrical properties such as dielectric constant, EOT, interface trap density and leakage current density through capacitance voltage and current voltage measurements. The interface state density extracted from the G–V measurement using Hill Coleman method. Sample annealed at 750 °C showed the lowest interface trap density (3.48 × 10¹¹ eV⁻¹ cm⁻²), effective oxide charge (1.33 × 10¹² cm⁻²) and low leakage current density (3.39 × 10⁻⁹ A cm⁻²) at 1.5 V.     

Parametric simulation of the back-surface field effect in the silicon solar cell

Recombination of minority carriers in the solar cell is a major contributing factor in the loss of quantum efficiency and cell power. While the surface recombination is dealt with by depositing a passivation layer of SiO₂ or SiN_x, the bulk recombination is minimized by use of nearly defect-free monocrystalline substrate. In addition, the back-surface field (BSF) effect has been very useful in aiding the separation of free electrons and holes in the bulk. In this study, the key BSF parameters and their effect on the performance of a typical p-type front-lit Si solar cell are investigated by use of Medici, a 2-dimensional device simulator. Of the parameters, the doping concentration of the BSF layer is found to be most significant. That is, for a p-type substrate of 1 × 10¹⁴ cm⁻³ acceptor concentration, the optimum doping concentration of the BSF layer is 1 × 10¹⁸ cm⁻³ or more, and the maximum cell power can be increased by 24%, i.e., 25.4 mW cm⁻² vs. 20.5 mW cm⁻², by using a BSF layer with optimum doping. With regards to the BSF layer thickness, the impact is less. That is, the maximum cell power is about 11% higher at 100 μm than at 5 μm, which translates to an increase of 1.2% μm⁻¹. In practice, therefore, it would be better to rely on the control of the doping concentration than the thickness in maximizing the BSF effect in real Si solar cells.     

Preparation of palladium membranes from the reaction of Pd(C3H3)(C5H5) with H2: wet-impregnated deposition

A new technique to prepare a palladium membrane for high-temperature hydrogen permeation was developed: Pd(C₃H₃)(C₅H₅) an organometallic precursor reacted with hydrogen at room temperature to decompose into Pd crystallites. This reaction together with sintering treatment under hydrogen and nitrogen in sequence resulted in the formation of dense films of pure palladium on the surface of the mesoporous stainless steel (SUS) support. Under H₂ atmosphere the palladium membrane could be sintered at 823 K to form a skin layer inside the support pores. The hydrogen permeance was 5.16×10⁻² cm³ cm⁻² cm Hg⁻¹ s⁻¹ at 723 K. H₂/N₂ selectivity was 1600 at 723 K.     

Study of thermal recrystallisation in Si implanted by 0.4-MeV heavy ions

A Si crystal layer on SiO₂/Si was implanted using 0.4-MeV Kr⁺, Ag⁺, and Au⁺ at ion fluences of 0.5 × 10¹⁵ to 5.0 × 10¹⁵ cm⁻². Subsequent annealing was performed at temperatures of 450° and 800° for 1 hour. The structural modification in a Si crystal influences ion beam channelling phenomena; therefore, implanted and annealed samples were investigated by Rutherford backscattering spectrometry under channelling (RBS-C) conditions using an incident beam of 2-MeV He⁺ from a 3-MV Tandetron in random or in aligned directions. The depth profiles of the implanted atoms and the dislocated Si atom depth profiles in the Si layer were extracted directly from the RBS measurement. The damage accumulation and changes in the crystallographic structure before and after annealing were studied by X-ray diffraction (XRD) analysis. Lattice parameters in modified silicon layers determined by XRD were discussed in connection to RBS-C findings showing the crystalline structure modification depending on ion implantation and annealing parameters.     

SNMS and XRD investigations of laser deposited YSZ buffer layers

Summary Secondary Neutral Mass Spectrometry (SNMS) and X-Ray Diffraction (XRD) were used to find optimum parameters for the in-situ pulsed laser deposition of ZrO₂/Y₂O₃ (YSZ) buffer layers on silicon (100) substrates. Homogeneous and nearly stoichiometric concentration depth profiles were found by SNMS for the laser deposited YSZ films. A peak of the SiO intensity during profiling of the YSZ/Si interface points to a SiO₂ intermediate layer. An increasing Y-deficit of the YSZ films was found by decreasing the laser energy density at the target. Epitaxial growth of the YSZ thin films was observed at an oxygen partial pressure lower than 10^–3 mbar, a substrate temperature of 600–800°C and a laser energy density at the target of about 8 J/cm².     

Pyroelectric and piezoelectric properties of new lead-free ceramics with composition Ba1-xNaxTi1-xO3

Ceramics with composition Ba_1-xNa_xTi_1-xNb_xO₃ are of either classical ferroelectric (0 ≤ × < 0.075) or relaxor ferroelectric types (0.075 ≤ x ≤0.55), and ferro- or antiferroelectric for compositions 0.55 < × ≤ 1. The dielectric study of ceramics with compositions close to NaNbO₃ showed a sharp peak of ε'_r without frequency dispersion. The value of T_c is decreasing as composition deviates from NaNbO₃. Ceramic samples are tetragonal at room temperature; they could be polarized and then show pyroelectric and piezoelectric properties up to 400K (p = 25nC.cm⁻².K⁻¹ and d₃₁30pC.N⁻¹ at 300K). This study aims at the preparation of environment-friendly lead-free relaxor ceramics which present a transition temperature close to room temperature.     

Structural and electrical characteristics of ALD-HfO2/n-Si gate stack with SiON interfacial layer for advanced CMOS technology

We report the fabrication of an ultra-thin silicon oxynitride (SiON) as an interfacial layer (IL) for n-Si/ALD-HfO₂ gate stack with reduced leakage current. The XRD, AFM, FTIR, FESEM and EDAX characterizations have been performed for structural and morphological studies. Electrical parameters such as dielectric constant (K), interface trap density (D_it), leakage current density (J), effective oxide charge (Q_eff), barrier height (Φ_bo), ideality factor (ƞ), breakdown-voltage (V_br) and series resistance (R_s) were extracted through C-V, G-V and I-V measurements. The determined values of K, D_it, J, Q_eff, Φ_bo, ƞ, V_br and R_s are 14.4, 0.5 × 10 ¹¹ eV⁻¹ cm⁻², 2.2 × 10⁻⁹ A/cm², 0.3 × 10¹³ cm⁻², 0.42, 2.1, −0.33 and 14.5 MΩ respectively. SiON growth prior to HfO₂ deposition has curtailed the problem of high leakage current density and interfacial traps due to sufficient amount of N₂ incorporated at the interface.     

A diode laser study of the Cl + CH3CO reaction

Real-time kinetic measurements are reported for the Cl + CH₃CO → CH₂CO + HCl reaction. The experiments utilize infrared spectroscopy to determine the time dependence of the ketene formed via this reaction and of the CO produced from the subsequent rapid reaction between chlorine atoms and ketene. The reaction is investigated over a pressure range of 10–200 torr and a temperature range of 215–353 K. Within experimental error the rate constant under these conditions is k_5a = (1.8 ± 0.5) × 10⁻¹⁰ cm³ s⁻¹. We have also examined the Cl + CH₂CO reaction and found it to have a rate constant of k₆ = (2.5 ± 0.5) × 10⁻¹⁰ cm³ s⁻¹ independent of temperature. © John Wiley & Sons, Inc. Int J Chem Kinet 29: 421–429, 1997.     

CdIn2S2Se2: A new semiconducting compound

The optical and electrical properties of CdIn₂S₂Se₂, a new layered semiconducting compound, were examined in the temperature range 10–300 K. The absorption edge at room temperature is observed at 1.95 eV, with a temperature shift of about 4.6 × 10⁻⁴ eV/K. Electrical transport is due to electrons, whose temperature independent density is about 3 × 10¹⁷ cm⁻³. The room-temperature mobility is 130 cm²/Vs, independent of the conduction direction. However, measurements parallel and perpendicular to c-axis show different linear decreases of the mobility with reciprocal temperature. Au/CdIn₂S₂Se₂/In Schottky diodes were produced.