Ion-activated interface adsorption of oxygen during silver deposition on silicon

The process of ion-activated oxygen adsorption on silicon has been investigated using an experimental concept with simultaneous deposition of silver films. Auger electron spectroscopy in combination with sputter depth profiling is subsequently performed to determine the amount of oxygen adsorbed at the Ag---Si interface. Noble gas ions (⁴He⁺, ²⁰Ne⁺ and ⁴⁰Ar⁺)with energies between 50 and 175 keV were used, and it was found that for substrate temperatures of 300–700 K the oxygen adsorption depends strongly on ion mass, ion energy and ion flux density. For flux densities of 5 × 10¹¹ cm⁻² s⁻¹ or less, adsorption dominates and, in particular, for light-ion bombardment the majority of adsorbed oxygen atoms form chemical bonds with the silicon surface atoms (Si---O). However, for heavy ions, physical sputtering starts to compete and limits the effective rate of adsorption. At sufficiently high ion fluxes the adsorption starts to decrease, and for all ions and energies used in this work it is found that, if the electronic energy deposition density exceeds a critical value of about 1.2 × 10²¹ eV cm⁻² s⁻¹, dissociation of the Si---O bonds prevails with a corresponding loss in the adsorbed oxygen quantity.     

Field-lowering carrier excitation in cadmium arsenide thin films

Cadmium arsenide is a II–V semiconductor which exhibits n-type intrinsic conductivity with high mobility up to μ_n=1.0–1.5 m²/V s. Potential applications include magnetoresistors and both thermal and photodetectors, which require electrical characterization over a wide range of deposition and measurement conditions. The films were prepared by vacuum evaporation with deposition rates in the range 0.5–6.0 nm/s and substrate temperatures maintained at constant values of 20–120°C. Sandwich-type samples were deposited with film thicknesses of 0.1–1.1 μm using evaporated electrodes of Ag and occasionally Au or Al. Above a typical electric field F_b of up to 5×10⁷ V/m all samples showed instabilities characteristic of dielectric breakdown or electroforming. Below this field they showed a high-field conduction process with logJ∝V^1/2, where J is the current density and V the applied voltage. This type of dependence is indicative of carrier excitation over a potential barrier whose effective barrier height has been lowered by the high electric field. The field-lowering coefficient β had a value of (1.2–5.3)×10⁻⁵ eV m^1/2/V^1/2 which is reasonably consistent with the theoretical value of β_PF=2.19×10⁻⁵ eV m^1/2/V^1/2 expected when the field-lowering occurs at donor-like centres in the semiconductor (Poole–Frenkel effect). For thinner films Schottky emission was more probable. The effects of the film thickness, electrode materials, deposition rate, and substrate temperature on the conductivity behaviour are discussed.     

Characterization of phosphorus oxinitride (PON) gate insulators for InP metal-insulator-semiconductor devices

A new gate-insulating film consisting of phosphorus oxinitride (PON) was formed on an (n)InP surface by vapour transport technique. The substrate temperature was in the range of 280–350°C. The deposited films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The interfacial properties of phosphorus oxinitride/(n)InP metal-insulator-semiconductor were investigated. The minimum value of the interface states density distribution (D_it), evaluated from high-frequency capacitance-voltage (C-V) measurement was 1.2 × 10¹¹ eV⁻¹ cm⁻² at about 0.48 eV below the conduction band edge of Inp.     

Physics and diagnostics of laser ablation plume propagation for high-Tc superconductor film growth

The formation, composition and propagation of laser-produced plasmas used for pulsed laser deposition (PLD) of Y₁Ba₂Cu₃O_7−x have been studied under film growth conditions. Four complementary spatially and temporally resolved in situ diagnostic techniques are applied to characterize the expansion of the laser plume into both vacuum and ambient gases: optical emission and absorption spectroscopy, fast ion probe measurements, and fast photography with a gated, image-intensified charge-coupled detector-array (ICCD) camera system. Transient optical absorption spectroscopy reveals large densities of ground state atoms, ions, and molecules in the plume as well as a slower component to the plume transport than is indicated by the plasma fluorescence and ion current.

Ablation into background gases results in scattering and attenuation of the laser plume. The exponential attenuation of the positive ion flux transmitted through 50–300 mTorr background oxygen is measured and used to define an overall ion-oxygen reaction cross-section σ_i−O2 = 2.3 × 10⁻¹⁶ cm² under the described film growth conditions.

The slowing of the laser plasma and formation of shock structures due to collisions with the ambient gas are described using ion probe measurements and ICCD photographic comparisons of expansion into vacuum and background oxygen. At the pressures used for PLD, distance-time R−t plots derived from the photographs and ion probe waveforms indicate that the higher pressure plume initially expands through the ambient gas in accordance with a drag model (where R = x_f[1 − exp( − βt)]), experiencing little slowing until a visible shock structure forms. Following a transition period, in which the plume appears to have two components, a single-component shock structure propagates in better agreement with a shock, or blast wave (R = ξ₀(E/₀)^1/5t^2/5) model.     

MBE growth and characterization of buried silicon oxide films on Si(100)

Silicon molecular beam epitaxy (Si-MBE) has been used to produce silicon oxide (SiO_x) films by evaporating Si on a heated Si(100) substrate in an ultra high vacuum system with an O₂ pressure of 10⁻⁶ to 10⁻⁴ mbar. Then the SiO_x films were overgrown with pure Si. The influence of the substrate temperature, the O₂ pressure and the Si deposition rate on the oxygen content in the SiO_x films and on the crystalline quality of the Si top-layer was investigated by Rutherford backscattering spectrometry and ion channeling. Epitaxial growth of the Si top-layer was observed up to a maximum concentration of ≈20 at.% oxygen content in the SiO_x film. Cross-sectional transmission electron microscopy shows that the structure of the SiO_x film changes duringa subsequent annealing procedure. Electron energy loss spectrometry proves that amorphous SiO₂ is formed and the development of holes indicates that the density of the as-grown SiO_x film is much lower than that of SiO₂. The specific for the as-grown SiO_x films was determined by I–V measurements.     

He+ 辐照对CLAM钢焊缝微观组织和性能的影响

在室温下用强度为70 keV的He⁺辐照CLAM钢焊缝,使用扫描电子显微镜(SEM)、透射电子显微镜(TEM)和连续刚度纳米压痕技术(CSM)对其表征,研究了He⁺辐照对CLAM钢焊缝的微观组织和性能的影响。结果表明,随辐照剂量的增大焊缝表面黑色孔洞的尺寸增大、密度提高;辐照剂量为1×10¹⁷ ions·cm^-2时,在两种焊缝中形成的位错环的尺寸分别约为18.97 nm、15.73 nm,数密度分别约为2.24×10²¹ m^-3、1.78×10²¹ m^-3,氦泡引起的辐照肿胀率分别约为1.7%和0.4%;辐照缺陷(位错环、氦泡)导致的辐照硬化率分别为49.0%和29.9%。与焊态焊缝相比,调质处理态焊缝的辐照损伤较弱,在一定程度上表明经调质处理后焊缝的抗辐照性能有所提高。     

Structural characterization of molecular beam epitaxy grown ZnSe-based layers on GaAs substrates for blue–green laser diodes

ZnSe films and fully developed p-on-n laser structures, including CdZnSe-active and ZnSSe-guiding layers were grown by molecular beam epitaxy (MBE) on lattice matched p-GaAs, p-AlGaAs and p-GaInP buffer layers. The structural characteristics of these layers were studied by combined cross-section and planar view transmission electron microscopy (TEM). The defect density of the ZnS_xSe_1−x epilayers was shown to be very low, <10⁵ cm⁻². However, on their interfaces with the GaAs substrate, a high density of small dislocation loops and clusters of the order of 3×10¹⁰ cm⁻² was observed. In situ TEM experiments revealed that dislocations and stacking faults (SFs) were generated under the electron beam influence. From them, the perfect dislocations were confined at the ZnSe/GaAs interface, while the SFs propagated to the ZnSe overgrowth or the GaAs substrate, having one of their partial dislocations at the interface. The generation of dislocations under the electron beam was not related to radiation damage but to thermal strain, which was developed by the heating effect due to differential thermal dilatation. Defects around the active zone of fully developed p-on-n laser structures were also studied. The nature of such defects was defined by Burgers vector determination experiments. The critical role of growth variations, such as compositional changes resulting in strain, in the MBE process of II–VI materials was demonstrated. The destructive role of the defected guiding layers in the laser structure was shown.     

On the formation of radiation-induced defects in fluoroaluminate glasses

The spectra of electron paramagnetic resonance (EPR) of fluoroaluminate glass (FAG-36) based on mineral usovite Ba₂CaMgAlF₁₄ were studied. The paramagnetic centers responsible for EPR signals were induced by ion bombardment of the substrates prepared from this glass. The N⁺, O⁺, Ar⁺ and Pb + ions with energy E = 150 keV were used. The integrated dose D was 2 × 10¹⁶ ions/cm². It is shown by means of isochronal anneal experiments and computer simulation of the EPR spectra that they contain four components: broad Gaussian line (GL) with g = 2.016 and σ oscillating in the range 30–40; two anisotropic spectra with g_z = 2.016, g_y = 2.009; g_x = 2.001 (FA₁) and g_z = 2.045; g_y = 2.010; g_x = 1.98 (FA₂) as well as narrow isotropic line of Lorentzian shape with g = 2.0025 and ΔH = 0.6 mT. The comparison of obtained results with literature data for γ-irradiated fluoride glasses and ion-implanted oxide glasses of different compositions permitted to conclude that GL is due to hole defects typical of fluoride glasses and localized on several anions (fluorines and oxygen(s)); anisotropic FA₁- and FA₂-spectra are attributed to molecular 0₂⁻-ions, and narrow isotropic signal is supposedly assigned to big molecular ions (O₂O⁻, 0₄⁻ , CO⁺, CO⁻) located in voids of damaged implantation layer.     

Low temperature UV/ozone oxidation formation of HfSiON gate dielectric

Physical and electrical properties of hafnium silicon oxynitride (HfSi_xO_yN_z) dielectric films prepared by UV ozone oxidation of hafnium silicon nitride (HfSiN) followed by annealing to 450 °C are reported. Interfacial layer growth was minimized through room temperature deposition and subsequent ultraviolet/ozone oxidation. The capacitance–voltage (C–V) and current–voltage (I–V) characteristics of the as-deposited and annealed HfSi_xO_yN_z are presented. These 4 nm thick films have a dielectric constant of 8–9 with 12 at.% Hf composition, with a leakage current density of 3×10⁻⁵ A/cm² at V_fb+1 V. The films have a breakdown field strength >10 MV/cm.     

Pulsed high energy density plasma processing silicon surface

Pulsed high energy density plasma (PHEDP) is a new material modification technique, which has the features of: high energy density (1–10 J/cm²), high plasma density (10¹⁴–10¹⁶ cm⁻³), high electron temperature (10–100 eV), high directed plasma velocity (10–100 km/s) and short pulse duration (10–100 μs). PHEDP interacting with material will result in rapid melting and re-solidification of surface layer with a quenching rate up to 10⁸ K/s; thus the material surface properties are modified. At the same time, PHEDP contains condensable ions or/and atoms, so a thin film layer can be formed on the modified surface and the deposited layer can be mixed with the substrate (or previous deposited layer) during following pulses. Therefore, this technique actually combines film deposition and mixing into one step. In this paper, we have reported the research results on the metallization of Si by PHEDP. The Ti---Si reactions under PHEDP are also discussed.     

Assessment of electrical and optical properties of heavily Fe-implanted semi-insulating InP

We report total compensation of InP layers n-doped to levels as high as n=2×10¹⁸ cm⁻³ by high temperature (>200°C) MeV Fe implantation and annealing. The electronic density and the active Fe (in the form of the Fe²⁺/Fe³⁺ deep acceptor states) profiles are obtained from the comparison between the current–voltage (I–V) characteristics and the outcome of a numerical simulation. These results are confirmed by photo-induced current transient spectroscopy (PICTS) experiments, which show a correlation between the Fe activation and the background doping concentration. A deeper insight into the properties of the Fe²⁺/Fe³⁺ centers is gained by Fourier transform infrared (FTIR) photoluminescence measurements, showing intense and sharp emission peaks at 3.5 μm, associated with Fe intracenter transitions. The corresponding lifetimes have been studied by time resolved integrated photoluminescence measurements.     

Molecular beam epitaxy of CdTe and CdxHg1−xTe on InSb

The crystalline quality of InSb substrates and their transparency in the 8–12 μm IR window compare favourably with those of CdTe. We report the first results obtained for Cd_xHg_1−xTe (CMT) layers grown using molecular beam epitaxy over a buffer layer of CdTe on InSb. The (100)-oriented InSb wafer is chemically cleaned prior to thermal treatment which may be accompanied by ion beam cleaning; this process leads to a (2x4) reconstructed surface. Characterization of the surface using Auger spectroscopy, UV photoemission spectroscopy and X-ray photoelectron spectroscopy shows that it is free from oxygen and carbon. CdTe is grown at a substrate temperature of 523 K using a single CdTe cell. When 0.5 μm of CdTe has grown, the substrate temperature is lowered and the CMT is deposited epitaxially using three different cells for cadmium, mercury and tellurium. The layers exhibit X-ray rocking curves 6' wide and n-type conductivity with n = 3× 10¹⁵ cm⁻³ and μ = 40 000 cm² V⁻¹ s⁻¹. Measurement of the strain in each layer shows that CMT is totally relaxed on the CdTe which in turn grows coherently on the InSb.     

High deposition rate of amorphous silicon thick layers using a gas mixture of 10% silane in hydrogen

The deposition rate of amorphous silicon of the order of 0.9 μm/h, has been obtained using a gas mixture of 10% silane (SiH₄) in hydrogen (H₂), with a RF source of 13.56 MHz. Best films were deposited at a total flow rate of 100–200 sccm, 300°C substrate temperature, 66.7 Pa, and RF power density of 150 mW/cm². The geometrical configuration of the reaction chamber included a gas injector that was specially designed for this purpose. Films were characterized by Fourier transform infrared (FTIR), secondary ion mass spectrometry (SIMS), and profilometer. In addition, thick p-i-n diodes were prepared and characterized, obtaining reverse current densities lower than 5×10⁻⁶ A/cm² at full depletion.     

Preparation of highly c-axis-oriented Bi4Ti3O12 thin films and their crystallographic, dielectric and optical properties

Bismuth titanate (Bi₄Ti₃O₁₂) thin films with a high c-axis orientation up to 99% were prepared on (100)-oriented silicon wafers by r.f. planar magnetron sputtering using a Bi₂TiO₅ ceramic target at a substrate temperature of 600 °C. From the Auger electron spectroscopy depth profile of the film, there is no evidence of interdiffusion of a specific element between the film and the substrate. Relative dielectric constant of these films depends on film thickness. The behavior was explained assuming a low-dielectric-constant interface layer. Using this assumption, the relative dielectric constant of Bi₄Ti₃O₁₂ film was estimated to be approximately 140. This value is close to that along the c axis in a bulk form. The remanent polarization and the coercive field were 0.8 μC cm⁻² and 20 kV cm⁻¹, respectively.     

Deposition and modification of titanium dioxide thin films by filtered arc deposition

Thin films of titanium dioxide have been deposited on glass substrates and conducting (100) silicon wafers by filtered arc deposition (FAD). The influence of the depositing Ti⁻ energy, substrate types and substrate temperature on the structure, density, mechanical and optical properties have been investigated. The results of X-ray diffraction (XRD) showed that with increasing substrate bias, the film structure on silicon substrates changes from anatase to amorphous and then to rutile phase without auxiliary heating, the transition to rutile occurring at a depositing particle energy of about 100 eV. However, in the case of the glass substrate, no changes in the structure and optical properties were observed with increasing substrate bias. The optical properties over the range of 300–800 nm were measured using spectroscopic elliosometery, and found to be strongly dependent on the substrate bias, film density and substrate type. The refractive index values of the amorphous, anatase and rutile films on Si were found to be 2.56, 2.62 and 2.72 at a wavelength of 550 nm, respectively. The hardness and elastic modulus of the films were found to be strongly dependent on the film density. Measurements of the mechanical properties and stress also confirmed the structural transitions. The hardness and elastic modulus range of TiO₂ films were found to be between 10–18 and 140–225 GPa, respectively. The compressive stress was found to vary from 0.7 to 2.6 GPa over the substrate bias range studied. The composition of the film was measured to be stoichiometric and no change was observed with increasing substrate bias. The density of the film varied with change in the substrate bias, and the density ranged between 3.62 and 4.09 g/cm³.     

Analysis of strain rate dependence of tensile elongation for a mechanical milling Al–1.1Mg–1.2Cu alloy tested at 748 K from a dislocation dynamics viewpoint

Tensile deformation was carried out for a mechanically milled and thermo-mechanically treated Al–1.1Mg–1.2Cu (at.%) alloy at 748 K and three nominal strain rates of 10⁻³, 10⁰, and 10² s⁻¹. Despite the prevailing belief that superplasticity occurs by grain boundary sliding which requires slow strain rates at high temperatures, the maximum elongation was observed at the intermediate strain rate of 10⁰ s⁻¹, neither at the lowest nor the highest strain rates. In order to explain this phenomenon, the true stress–true strain behaviors at these three nominal strain rates were analyzed from a viewpoint of dislocation dynamics by computer-simulation with four variables of the thermal stress component σ*, dislocation immobilization rate U, re-mobilization probability of unlocked, immobile dislocations Ω and dislocation density at yielding ρ₀. It can then be concluded that the large elongation (>400% in nominal strain) at the intermediate strain rate is produced by a combination of a very large Ω and a moderate U, resulting in a large strain rate sensitivity m value.     

Sc掺杂Nd:CaF2激光晶体的结构及其光谱性能参数

采用温度梯度法生长了0.5at% Nd、xat% Sc:CaF₂(x=0, 2, 5, 8)系列晶体, 测试了晶体的吸收光谱、荧光光谱和荧光寿命。研究发现发射强度和荧光寿命随着Sc³⁺离子浓度的增加而提高。通过改变Sc³⁺离子的浓度发现, 当掺杂5at% Sc³⁺时可以获得最大的吸收截面为1.42×10^-20 cm²。另外, 掺入Sc³⁺使共掺晶体在吸收光谱796 nm处产生新峰。综上, 通过调节Sc³⁺离子浓度, 可以改变Nd³⁺离子的局域结构, 优化晶体的光谱性能。     

Dielectric properties of AlN films prepared by laser-induced chemical vapour deposition

The dielectric properties and electrical conductivity of AlN films deposited by laser-induced chemical vapour deposition (LCVD) are studied for a range of growth conditions. The static dielectric constant is 8.0 ± 0.2 over the frequency range 10²−10⁷ Hz and breakdown electric fields better than 10⁶ V cm⁻¹ are found for all films grown at temperatures above 130°C. The resistivity of the films grown under optimum conditions (substrate temperature above 170°C, NH₃/TMA flow rate ratio greater than 300 and a deposition pressure of 1–2 Torr) is about 10¹⁴ Ω cm and two conduction mechanisms can be identified. At low fields, F < 5 × 10⁵ V cm⁻¹ and conductivity is ohmic with a temperature dependence showing a thermal activation energy of 50–100 meV, compatible with the presumed shallow donor-like states. At high fields, F > 1 × 10⁶ V cm⁻¹, a Poole-Frenkel (field-induced emission) process dominates, with electrons activated from traps at about 0.7–1.2 eV below the conduction band edge. A trap in this depth region is well-known in AlN. At fields between 4 and 7 × 10⁵ V cm⁻¹ both conduction paths contribute significantly. The degradation of properties under non-ideal growth conditions of low temperature or low precursor V/III ratio is described.     

SiC nanocrystals embedded in oligoetheracrylate photopolymer matrices; new promising nonlinear optical materials

Photoinduced optical phenomena in SiC nanocrystallites embedded within the photo-polymer oligoetheracrylate matrices have been studied using experimental nonlinear optics, particularly photoinduced optical second harmonic generation (SHG). The YAG-Nd-laser (λ=1.06 μm; W=30 MW; pulse duration within the 30–50 ps) was used as a source of pumping light and the nitrogen laser (λ=337 nm) has been applied as a source of the photoinducing light. With increasing intensity of the photoinducing beam, the SHG (λ=0.53 μm) signal increased and achieved a maximum (χ₂₂₂=10.1 ± 0.13 pm/V) at a photon flux of about 1.61 GW/cm². With decreasing temperature, the SHG signal strongly increases within the temperature range 25–30 K. Time-dependent probe–pump measurements indicate an existence of the SHG maximum for a pump–probe time delay of about 20 ps. The SiC hexagonal structural components play a key role in the observed photoinduced nonlinear optical effects. Large values of the nonlinear optical constants as well the good technological parameters open a possibility to enhance the nonlinear optical susceptibilities.     

Highly conducting indium tin oxide (ITO) thin films deposited by pulsed laser ablation

Highly conducting and transparent indium tin oxide (ITO) thin films were prepared on SiO₂ glass and silicon substrates by pulsed laser ablation (PLA) from a 90 wt.% In₂O₃-10 wt.% SnO₂ sintered ceramic target. The growths of ITO films under different oxygen pressures (P_O2) ranging from 1×10⁻⁴–5×10⁻² Torr at low substrate temperatures (T_s) between room temperature (RT) and 200°C were investigated. The opto-electrical properties of the films were found to be strongly dependent on the P_O2 during the film deposition. Under a P_O2 of 1×10⁻² Torr, ITO films with low resistivity of 5.35×10⁻⁴ and 1.75×10⁻⁴ Ω cm were obtained at RT (25°C) and 200°C, respectively. The films exhibited high carrier density and reasonably high Hall mobility at the optimal P_O2 region of 1×10⁻² to 1.5×10⁻² Torr. Optical transmittance in excess of 87% in the visible region of the solar spectrum was displayed by the films deposited at Po₂≥1×10⁻² Torr and it was significantly reduced as the P_O2 decreases.