Co/n-GaN SDs has been prepared by magnetron DC sputtering technique. The Co/n-GaN SDs have annealed at 600 °C after a post-deposition. The diode parameters such as the ideality factor, barrier height and Richardson constant have been determined by thermionic emission (TE) equation within the measurement temperature range 60–320 K by the steps of 20 K in the dark. It has been seen that the parameters depend on the measurement temperature indicating the presence of a lateral inhomogeneity in the Schottky barrier. Therefore, it has been modified the experimental data by the thermionic emission (TE) mechanism with Gaussian distribution of the barrier heights by using Tung’s theoretical approach that the Schottky barrier consists of laterally inhomogeneous patches of different barrier heights. Thus, the modified Richardson plot according to Tung’s barrier inhomogeneity model [8] has given a Richardson constant of 27.66 A/(cm2 K2).

The role of laser assisted atom probe tomography (APT) in microelectronics is discussed on the basis of various illustrations related to SiGe epitaxial layers, bipolar transistors or MOS nano-devices including gate all around (GAA) devices that were carried out at the Groupe de Physique des Matériaux of Rouen (France). 3D maps as provided by APT reveal the atomic-scale distribution of dopants and nanostructural features that are vital for nanoelectronics. Because of trajectory aberrations, APT images are subjected to distortions and local composition at the nm scale may either be biased. Procedures accounting for these effects were applied so that to correct images.

Charge carrier trapping in thin films of lyotropic chromonic liquid crystals (LCLCs) based on ionic perylene diimide derivative and in chemically-similar neutral N,N′-dipentyl-3,4,9,10-perylene-dicarboximide (PTCDI-C5) films is investigated by thermally-stimulated luminescence (TSL) technique. The LCLC films comprise elongated molecular aggregates featuring a long-range orientational order. The obtained results provide direct evidence for the improved energetic ordering (smaller effective energetic disorder) in aggregated LCLC films as compared to conventional PTCDI-C5 films. The width of the density-of-state distribution of 0.09 eV and 0.13 eV was estimated for the LCLC and PTCDI-C5 films, respectively. Relatively small effective energetic disorder in LCLC films is ascribed to formation of macroscopically larger LCLC aggregates.

The capacitance between arbitrary two sites (vertices) in infinite triangular and honeycomb networks is studied by using Green’s function. Recurrence formulas for capacitance between arbitrary sites of the triangular lattice are obtained. The capacitance for the honeycomb lattice is shown to be expressed in terms of the one for the triangular lattice.

We present magnetotransport measurements on a high electron density AlGaN/GaN heterostructure with two subbands populated at T = 1.6 K. The transport scattering times, τtr, of each subband are first derived at low magnetic field by taking into account the magneto-intersubband scattering term. Then the quantum scattering times, τq, are extracted from independent Dingle plots, obtained at higher magnetic fields. All scattering times are studied as a function of the total electronic density, increased by the persistent photo-conductivity effect. A standard modelization, based on all common scattering mechanisms, reveals that the transport scattering time is governed by the short-range AlGaN/GaN interface roughness (IR) scattering, whereas the quantum scattering time is due to the smooth potential induced by remote ionized impurities (II) at the GaN surface. This intermediate situation of mixed disorder, where the τtr/τq ratio is greater than one, does not indicate that the mobility is limited by Coulomb scattering. It is due to the unusual condition, τtrII≫τtrIR≫τqII$ {\tau }_{\mathrm{t}r}^{\mathrm{II}}\gg {\tau }_{\mathrm{t}r}^{\mathrm{IR}}\gg {\tau }_{\mathrm{q}}^{\mathrm{II}}$.

In this paper, the hole carrier mobility of organic semiconductor N,N′-diphenyl-N,N′bis(1,1′-biphenyl)-4,4′-diamine (NPD) was researched by negative differential susceptance spectra (−ΔB = −w(C − Cgeo) ~ f). Under the condition of space charge limited current (SCLC), through solving the drift current equation and Poisson equation and simulating the spectra −ΔB = −w(C − Cgeo) ~ f, the relationship between the peak of −ΔB = −w(C − Cgeo) ~ f spectra (1/ƒp = τp) and the transfer time of carrier (τdc) could be achieved to be τdc = k × τp. So the hole-only device of ITO/NPD/Ag was fabricated to determine the capacitance spectra, and through which its −ΔB = −w(C − Cgeo) ~ f could be plotted. According to the relationship of τdc = k × τp, where k was determined to be 0.56, the transfer time and further the carrier mobility could be obtained. The carrier mobility depended on the electric field according to Poole-Frenkel model was further investigated in this report.

The influence of interfacial charges on the device characteristics of bi-layers structure LEDs with poly[5-methoxy-2-octyloxy-1,4-phenylenevinylene] (MO-PPV) as active polymer layer is investigated. The concept to improve device performance is presented using: a diacetate cellulose (DAC) and a new synthetized 5-{2-(2-chloroethoxy)ethoxy}-2-{(E)-(2-pyridyl)azo}phenol (PDEG) components. The DAC and mixed (DAC+PDEG) layers were inserted between indium tin oxide (ITO) and MO-PPV polymer. The optical properties (UV-Vis) of MO-PPV, PDEG and mixed (DAC+PDEG) in solutions were studied and compared to those on thin films. Detailed current-voltage measurements of the bi-layers devices showed improvements of the threshold voltage (Vth) of the ITO/(DAC+PDEG)/MO-PPV/Al device attributed to the enhancement of carriers injection and transport resulted from the modified electrode structures. Conduction mechanisms of structure LEDs were matched with space-charge-limited current (SCLC) one. The impedance spectra for all devices can be discussed in terms of an equivalent circuit model designed as a parallel resistor Rp and capacitor Cp network in series with resistor Rs. The ITO/(DAC+PDEG)/MO-PPV/Al device showed the lowest impedance attributed to the removal of contaminants and to changes in the work function of ITO. The frequency-dependent electrical properties of the ITO/(DAC+PDEG)/MO-PPV/Al structure is analyzed by impedance spectroscopy as function of bias. We have extracted numerical values of the equivalent circuit model parameters by fitting experimental data. Their evolution with bias voltages has shown that the SCLC mechanism is characterized by an exponential trap distribution.

In this work, we have investigated the structural, optical and electrical properties of rare earth co-doped zinc oxide thin films prepared by spray pyrolysis technique. X-ray diffraction has shown that the films are polycrystalline and textured with the c-axis of the wurtzite structure along the growth direction. Scanning electronic microscopy and transmission electronic microscopy were used to study the films composition and morphology. Photoluminescence measurements showed that all the films have a strong emission band at around 380 nm. Layers with electrical resistivity values as low as 5.7 × 10−2 Ω cm were obtained.

In order to study the influence of palladium atom on structural and hyperfine properties, Fe100–xPdx films (x = 15, 20 and 36 at.%) were deposited by evaporation method onto a Si (1 0 0) substrate. They were then characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS). X-ray diffraction analysis shows the presence of supersaturated solid solution with bcc structure for Pd concentration of 15% and 20%. However, for 36% of Pd, in addition to the supersaturated α-FePd (bcc) phase, another disordered FePd3 phase with fcc structure is present. The grain size did not change with Pd concentration and was about 11 nm, and the lattice parameter increased from 0.287 Å to 0.290 Å with an increasing Pd concentration. The adjustment of Mössbauer spectra confirms the results obtained by X-ray diffraction. Moreover, the Mössbauer spectra have shown that a magnetic texture is present for samples with 20 and 36%. For these Pd concentrations, we believe that a development of an out-of plane magnetic anisotropy occurs in our films.

In this paper, we present the fabrication and characterization of sputter deposited thin-film Cr-CrOx-Cr MIM diodes for application in millimeter wave detectors. The oxide layers were grown by thermal oxidation of the first deposited Cr electrode at 300 °C and at atmospheric pressure. The appreciable nonlinearity shown by these diodes confirms their viability in millimeter wave and infrared applications. The fabricated MIM structures exhibited sensitivity as high as 2.58 V−1 at Vbias of 0.3 V. Additionally, numerical integration of Simmons tunneling equations were utilized to extract the MIM diodes parameters. The correlation between the extracted parameters, the diodes performance and the fabrication conditions would be very valuable to effectively design and fabricate structures with improved performance.

First principles studies about the influence of electric field and anisotropic oxygen vacancy on the dielectric properties of rutile titanium dioxide (TiO2) are investigated. These results demonstrate that dielectric properties of perfect TiO2 presents dependent on the low electric field that less than 5.2 MV/cm. As a comparison, the dielectric properties of defected TiO2 in (1 1 0) plane and [1 1 0] direction show more sensitive to high electric field. Further more, considering the different positions of oxygen vacancy, the oxygen vacancy locates in (1 1 0) plane of defected TiO2 appears more active to high electric field than it does in [1 1 0] direction. The effect of electric field and oxygen vacancy induce the distorted supercell structure and broken bond between the nearer oxygen atoms and titanium atoms. Moreover, the oxygen vacancy locates in (1 1 0) plane of defected TiO2 can create more potential broken bond. These results account for the difference of dielectric properties in perfect TiO2 and defected TiO2.

PTFE-metal composites are promising candidates for use as sensor materials. In present study PTFE-Au composite layers were deposited by alternated ablation of pressed Teflon pellets and gold plates with focused beam of an ArF excimer laser at 6 J/cm2 fluence, while keeping the substrate at 150 °C temperature. The morphology and chemical composition of the ~3–4 μm average thickness layers was studied by electron microscopy and energy dispersive X-ray spectroscopy. The layers were mainly formed of PTFE gains and clusters which are covered by a conductive Au film. For testing the applicability of such layers as sensing electrodes, composite layers were prepared on one of the two neighbouring electrode of a printed circuit board. Cholesterol and glucose solutions were prepared using 0.1M NaOH solvent containing 10% Triton X-100 surfactant. The electrodes were immersed in the solutions and voltage between the electrodes was measured while a constant current was drawn through the sample. The influence of the analyte concentration on the power spectral density of the voltage fluctuation was studied.

We present calculation of critical voltage for AlGaN/GaN high electron mobility transistors (HEMTs) with GaN cap layer. The calculation includes mechanical stress and relaxable energy in the GaN/AlGaN barrier layer. Under high voltage conditions, the high electric field results in an increase in stored relaxable energy. If this exceeds a critical value, crystallographic defects are formed. This degradation mechanism is voltage driven and characterized by a critical voltage beyond which non-reversible degradation takes place. The dependence of the GaN cap layer’s thickness on the critical voltage has been discussed. The calculated results indicate that thicker GaN cap layer results in higher critical voltage.

Plasma processing is an approach to modify the surface structure for improved performance of nitride semiconductor using in light emitting diodes. In this work, RF sputtered GaN thin films were synthesized on Si (1 0 0) substrates and processed at two different plasmas (N2 and O2) at various flow rates. The surface nature of plasma processed thin films was characterized using atomic force microscope (AFM) and scanning electron microscope (SEM). Energy dispersive spectrum (EDS) of all samples was recorded to do elemental analysis. Noticeable changes on surface morphology were recorded for the plasma processed GaN thin films at high flow rate (>20 sccm). The roughness and particle size of thin film got decreased as the flow rate of gases increased. Low value in surface roughness (0.26 nm) and particles size (14 nm) was observed at 30 sccm flow rate of O2. SEM images also revealed the surface modification at high gas flow rates during plasma process. Nitrogen deficient GaN thin film was confirmed by EDS spectra and improved N2 concentration was achieved for N2 and O2 plasma processing upto 20 sccm flow rates. I-V characteristics showed the Schottky-contact behavior for all thin films and revealed the improved surface quality to make good ohmic contact for the film processed at high gas flow rate (>30 sccm).

Application of the radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) technique was studied to fabricate amorphous and nanocrystalline silicon (a-Si and nc-Si) thin films for photovoltaic devices at substrate temperature of 200 °C. Amorphous-crystalline transition of silicon thin films in working conditions of PECVD system was shown as a function of deposition parameters, i.e., dilution ratio of silane (SiH4) in hydrogen, total gas pressure during deposition and RF excitation power density. The crystalline volume as well as grain size of nanocrystalline silicon films could be successfully controlled by tuning those deposition parameters. Micro Raman scattering spectroscopy and spectroscopic ellipsometry (SE) methods were used to characterize the structure and crystallization of the deposited silicon thin films. We could make nc-Si thin films with various crystalline volumes. Nc-Si grain size was also controlled and was in the range of 3–5 nm.

A wide-angle broadband absorber which is realized by periodic structures containing graphene-based hyperbolic metamaterials (GHMM) and isotropic medium is theoretically investigated. The GHMM is composed of monolayer graphene and conventional dielectric, which the refractive index can be tuned by the chemical potential, the thickness of dielectric and phenomenological scattering rates, respectively. A periodic structure of GHMM can obtain a broadband absorption which is shown to absorb roughly 70% (relative bandwidth is larger than 45%) of all available electromagnetic wave in absorption bandwidth at normal incident angle. Compared with some previous designs, our proposed structure has a relative bandwidth over a broad frequency range in mid-infrared. This kind periodic structures offer additional opportunities to design novel optoelectronic devices.

Based on the finite-differences approach, we study the electronic properties of two-dimensional electron gas under an inhomogeneous magnetic field. Such structure can be realized by deposition of ferromagnetic strips on the surface of a semiconductor heterostructure. It is found that the system exhibits rich band structures. Many bound states are twofold degenerate for θ = π/2, which defines the magnetization direction in the ferromagnetic strips, while few degenerate state exist for θ = 0. Despite of this, there are three kinds of electronic states in our system: the extended, localized and intermediate ones, which is very different from the case of absence of magnetic field.

Hierarchical Zn0.5Cd0.5S nanohexagon dendrites were synthesized by a one-step hydrothermal method. The Zn0.5Cd0.5S nanohexagon dendrites were made up of nanohexagons with a side length of about 90 nm. The nanohexagons were regularly arranged forming as embranchments which were parallel to each other along certain hexagonal directions. Furthermore, these embranchments made up primary trunks shaping as dendrites. The growth mechanism of Zn0.5Cd0.5S nanohexagon dendrites was proposed in which molecular soft template and lowest energy principle played key roles. By adjusting the composition of the reactants, a series of ZnxCd1–xS solid solutions could be obtained. The morphology of the synthesized ZnxCd1–xS depended much on the x value. The UV-vis spectra absorb edges of the ZnxCd1–xS samples continuously shifted indicating the changes of the band gap.

The magnetic properties of Co thin films obliquely evaporated under silicon and glass substrates are investigated using alternating gradient field magnetometer (AGFM) and magnetic force microscopy (MFM) techniques. The effects of the magnetic layer thickness and the deposition angle are studied. As results, it is found a decrease of the coercive field from 250 Oe, for t = 20 nm, to 95 Oe, for t = 400 nm, and a decrease of the anisotropy field from 1.6 kOe for 20 nm Co thick film, to 0.95 kOe for 200 nm Co thick film. An increase of these fields with the increase of the deposition angle is also found. The easy axis of the saturation magnetization lies in the film plane, whatever is the substrate nature. MFM images reveal well-defined stripe patterns, particularly for the thickest films, where the magnetocrystalline anisotropy is dominant. These results, and others, are presented and discussed.

In this article, the vibrational behavior of a microcantilever (MC) with an extended piezoelectric layer in the air ambient undergoes examination. To model the vibrational motion of this type of cantilever, the Hamilton’s principle has been used. For this purpose, the MC vibrational equation has been derived by the assumption of the continuous beam based on the Euler-Bernoulli beam theory. By adopting the finite element method (FEM), the MC differential equation has been solved. In the present simulation not only van der Waals and contact forces but also the capillary forces resulting from the condensation of the water vapors in air on MC tip have been considered. The results illustrate that the force between the sample surface and the probe affects the MC amplitude; furthermore, it causes the reduction in the resonance frequency. In addition, to reduce the time delay during topography from the surface roughness, it is better to select MCs with larger width and length and smaller thickness. Furthermore, the results indicate that the best imaging takes place when the vibration is in its second vibrational mode. Finally, the effects of MC geometric parameters on the time delay between the starting moment of surface roughness and the moment of variation in the MC amplitude (surface roughness topography) have been analyzed.