Temperature and field dependence of stress induced leakage currents in very thin (<5 nm) gate oxides

We have studied the electric field and temperature dependence of stress induced leakage currents that appear in 3.8 and 4.7 nm thick SiO₂ oxides of metal oxide semiconductor structures after Fowler–Nordheim (FN) electron injections from the poly-Si gate and localized hot-hole injections from the p-Si substrate. Constant voltage or constant current stressing modes were used, which did not produce any difference in stress induced leakage currents (SILC) increase. A Schottky law apparently fits the field dependence of such currents in 4.7 nm samples, but the slope found in 3.8 nm thick oxides disagrees with the theoretical prediction. Moreover, the field dependence of the thermal activation energy found is much less than the Schottky prediction, which rules out the possibility of a thermoionic process to fully explain such currents in our samples. We show that a direct tunneling law, modified to account for a mechanism assisted by stress induced baricentric neutral defects, does correctly fit the oxide field dependence of these currents and is consistent with the observed thermal activation energy.     

Non-equilibrium gate tunneling current in ultra-thin (<2 nm) oxide MOS devices

The modeling of the electrical properties of ultra-thin (<2 nm thick) oxide metal–oxide–semiconductor (MOS) structures requires the self-consistent solution of the Schrödinger and the Poisson equations. To calculate the change density profile required by the Poisson equation, the occupancy of the quantum electronic states solution of the Schrödinger equation is a key issue. The most widely used approximation consists in assuming that the states that impinge from cathode and anode are occupied according to the Fermi–Dirac distribution with a quasi-Fermi (imref) level equal to that of the corresponding reservoir. The cathode and anode quasi-Fermi levels differ in the applied bias. In this work, we study the failure of this quasi-equilibrium approximation in the case of a MOS structure biased in accumulation. Our approach consists in considering the balance between inelastic scattering of electrons in the accumulation layer and the tunneling through the oxide. Using this procedure, we estimate that this quasi-equilibrium approximation fails for oxide thickness between 1 and 2 nm. Finally, we argued that kinetic treatments of transport are required for thinner oxides.     

Structure and optical properties of multilayer X-ray mirrors for long wave part (3.1–4.4 nm) of “water window”

Structure and optical properties (at λ - 0.154 nm and λ - 3.16 nm) of W Ti, W TiN, W Sc, and Cr Sc multilayer X-ray mirrors for long wave part of “water window”' wavelength range (3.1–4.4 nm) were studied by methods of X-ray diffractometry and cross-sectional electron microscopy. The reflectivities at λ - 0.154 nm are increased going from W TiN, Cr Sc, W Ti to W Sc multilayers. Cr Sc mirrors have highest reflectivity and resolution at λ - 3.16 nm. Influence of the ambient atmosphere on optical properties of multilayer mirrors is shown.     

Growth and characterization of a novel organic NLO crystal: 4 – ethoxy benzaldehyde – n – methyl 4 – stilbazolium tosylate

The organic material 4‐Ethoxybenzaldehyde‐N‐methyl 4‐Stilbazolium Tosylate (EBST) is a new NLO material and new derivative in Stilbazolium Tosylate family. In this work we synthesized the EBST, the derivative of DAST. By slow evaporation method, we have grown the EBST crystal. Powder XRD confirms the crystalline property, the lattice parameters are calculated from single crystal XRD data and the molecular structure also revealed. The crystal system is found as monoclinic. The crystalline perfection is assessed by the high‐resolution X‐ray diffractometry. A single and reasonably sharp peak observed in the diffraction curve indicates that the quality of the crystal is quite good without having any internal structural grain boundaries. The FTIR and proton NMR study confirm the presence of functional groups. From the UV – Vis Far IR absorption spectra the good transparency is revealed. The Kurtz Perry SHG test confirms the NLO property of the EBST crystal grown and it is 11 times greater than urea. The melting point of the grown crystal is found to be 237°C from the DSC curve. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation,structure and photoluminescence properties of SiO2–coated ZnS nanowires

It is essential to passivate one‐dimensional (1D) nanostructures with insulating materials to avoid crosstalking as well as to protect them from contamination and oxidation. The structure and influence of thermal annealing on the photoluminescence properties of ZnS‐core/SiO₂‐shell nanowires synthesized by the thermal evaporation of ZnS powders followed by the sputter deposition of SiO₂ were investigated. Transmission electron microscopy and X‐ray diffraction analyses revealed that the cores and shells of the core‐shell nanowires were single crystal zinc blende‐type ZnO and amorphous SiO₂, respectively. Photoluminescence (PL) measurement showed that the core‐shell nanowires had a green emission band centered at around 525 nm with a shoulder at around 385 nm. The PL emission of the core‐shell nanowires was enhanced in intensity by annealing in an oxidative atmosphere and further enhanced by subsequently annealing in a reducing atmosphere. Also the origin of the enhancement of the green emission by annealing is discussed based on the energy‐dispersive X‐ray spectroscopy analysis results. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The double phosphates MIMIIPO4 (MI – Na,K; MII – Mg,Mn, Co,Ni, Zn) – synthesis from chloride melts and characterization

The particularities of the chemical interaction in systems M^IPO₃‐M^IIO(or Mn₂O₃)‐M^ICl (M^I – Na, K; M^II – Mg, Co, Ni, Zn) have been investigated at the temperature 1073 K and molar ratios P/M^x = 1 or 2 and M^ICl/(M^IPO₃ + M^IIO(or Mn₂O₃)) = 30. The conditions of formation of complex phosphates M^ІM^IIPO₄ and Na₄Ni₃(PO₄)₂P₂O₇ have been found. Influences of the nature of alkali and bivalent metals on the products composition were discussed. The advantages of chloride melts using (synthesis time reduction and temperature reducing) for preparing of complex phosphates were shown. The synthesized compounds have been characterized using the powder X‐ray diffraction, Fourier transform infrared and diffuse reflectance spectroscopies.     

Wave-mechanical study of gate tunneling leakage reduction in ultra-thin (<2 nm) dielectric MOS and H-MOS devices

The downsizing of the metal oxide semiconductor field effect transistor (MOSFET) to dimensions <0.1 μm in the next years requires the adoption of <2 nm thick gate oxides, which unfortunately give rise to a significant direct tunneling current. We apply in this paper a self-consistent one-dimensional Schrödinger–Poisson model to study MOSFET channel architectures likely to reduce this leakage. They consist in either increasing the insulator thickness using a larger permittivity nitride/oxide stack or burying the channel thanks to a tensile strained IV–IV heterostructure. It is shown that both solutions yield separately a reduction, and that the combination of these two strategies offers promising opportunities to fulfill ultimate complementary metal oxide semiconductor technology (0.1 μm) requirements regarding gate oxide downsizing.     

Optical properties of Ga1–xInxAs LPE-layers and p-n structures

The multiple layer structure nGaAs(n Ga_1–xIn_xAs) p Ga_1–xIn_xAs (0 ≦ × ≦ 0.18) was realized by liquid phase epitaxy from In–Ga–As-melts on (111)-oriented GaAs substrates. The InAs-content of the mixed crystal layers was found to be dominating for crystal perfection and growth rate. The cathodoluminescence spectra of p-and n-type Ga_1–xIn_xAs and spectral distribution of the electroluminescence from pn-junctions were measured at T = 77 K and 300 K. The external quantum efficiency wa found to have a maximum for diodes with x ≈ ≈ 0.006. This is caused by the decrease of the optical absorption with increasing x and increasing dislocation density on the other hand.     

Nucleation-growth process of scale electrodeposition – influence of the magnesium ions

Electrodeposition of CaCO₃ was studied under the influence of magnesium ions present in a carbonically pure water. The investigation was performed using electrochemical, gravimetric and optical methods. The chronoamperometric measurements confirmed the inhibiting property of Mg²⁺ when its concentration is higher than 120 mg L⁻¹ in a solution containing 160 mg L⁻¹ of Ca²⁺. The optical technique led the nucleation-growth process to be accessed by means of an optical microscope positioned behind a transparent electrode. The increase of Mg²⁺ concentration changed drastically the calcite morphology. At 360 mg L⁻¹ of Mg²⁺, the calcite morphology was optically amorphous but the Raman spectrum confirmed its structure. The crystal growth was recorded in situ and the image analysis software characterised the nucleation process as well as the growth rate of the crystals. It allowed the influence of the Mg²⁺ ions on the crystallisation process of CaCO₃ to be quantified.     

Phase Interaction in the Systems Sodium Selenate – Copper Selenate – Water and Sodium Selenate – Zinc Selenate – Water at 25 °C

The phase equilibrium in the systems Na₂SeO₄–CuSeO₄–H₂O and Na₂SeO₄–ZnSeO₄–H₂O were studied and it was established that new phases were obtained – double salts with a composition: Na₂Cu(SeO₄)₂ · 2 H₂O and Na₂Zn(SeO₄)₂ · 2 H₂O. The fields of phase equilibrium of the double salts in the triple systems were determined. The composition of the new phases was investigated by the Schreinemackers' method of physico-chemical analysis, and the number of the water molecules of crystallization – by thermogravimetrical analysis. An X-ray diffraction analysis of the new phases obtained was done.