Temperature dependent current-voltage and capacitance-voltage characteristics of chromium Schottky contacts formed by electrodeposition technique on n-type Si

The variations in the electrical properties of Cr Schottky contacts formed by electrodeposition technique on n-type Si substrate have been investigated as a function of temperature using current-voltage (I-V) and capacitance-voltage (C-V) measurements in the temperature range of 80-320 K by steps of 20 K. The basic diode parameters such as ideality factor (n) and barrier height (Φ_b) were consequently extracted from the electrical measurements. It has been seen that the ideality factor increased and the barrier height decreased with decreasing temperature, when the I-V characteristics were analyzed on the basis of the thermionic emission (TE) theory. The abnormal temperature dependence of the Φ_b and n and is explained by invoking two sets of Gaussian distribution of barrier heights at 320-200 K, and 180-80 K. The double Gaussian distribution analysis of the temperature-dependent I-V characteristics of the Cr/n-type Si Schottky contacts gave the mean barrier heights of 0.910 and 0.693 eV and standard deviations (σ_s) of 109 mV and 72 mV, respectively. Then, these values of the mean barrier height have been confirmed with the modified ln(I₀/T²) − q²/2k²T² versus 1/T plot which belongs the two temperature regions.     

Electronic properties of Al/DNA/p-Si MIS diode: Application as temperature sensor

The current-voltage (I-V) measurements were performed in the temperature range (200-300 K) on Al/DNA/p-Si Schottky barrier type diodes. The Schottky diode shows non-ideal I-V behaviour with ideality factors n equal to 1.34 ± 0.02 and 1.70 ± 0.02 at 300 K and 200 K, respectively, and is thought to have a metal-interface layer-semiconductor (MIS) configuration. The zero-bias barrier height Φ_b determined from the I-V measurements was 0.75 ± 0.01 eV at 300 K and decreases to 0.61 ± 0.01 eV at 200 K. The forward voltage-temperature (V_F-T) characteristics were obtained from the I-V measurements in the temperature range 200-300 K at different activation currents (I_F) in the range 20 nA-6 μA. The V_F-T characteristics were linear for three activation currents in the diode. From the V_F-T characteristics at 20 nA, 100 nA and 6 μA, the values of the temperature coefficients of the forward bias voltage (dV_F/dT) for the diode were determined as −2.30 mV K⁻¹, −2.60 mV K⁻¹ and −3.26 mV K⁻¹ with a standard error of 0.05 mV K⁻¹, respectively.     

On the mechanism of current-transport in Cu/CdS/SnO2/In-Ga structures

The structural and optical properties of CdS films deposited by evaporation were investigated. X-ray diffraction study showed that CdS films were polycrystalline in nature with zinc-blende structure and a strong (1 1 1) texture. The study has been made on the behavior of Cu/n-CdS thin film junction on SnO₂ coated glass substrate grown using thermal evaporation method. The forward bias current-voltage (I-V) characteristics of Cu/CdS/SnO₂/In-Ga structures have been investigated in the temperature range of 130-325 K. The semi-logarithmic lnI-V characteristics based on the Thermionic emission (TE) mechanism showed a decrease in the ideality factor (n) and an increase in the zero-bias barrier height (Φ_Bo) with the increasing temperature. The values of n and Φ_Bo change from 8.98 and 0.29 eV (at 130 K) to 3.42 and 0.72 eV (at 325 K), respectively. The conventional Richardson plot of the ln(I_o/T²) vs q/kT shows nonlinear behavior. The forward bias current I is found to be proportional to I_o(T)exp(AV), where A is the slope of ln(I)-V plot and almost independent of the applied bias voltage and temperature, and I_o(T) is relatively a weak function of temperature. These results indicate that the mechanism of charge transport in the SnO₂/CdS/Cu structure in the whole temperature range is performed by tunneling among interface states/traps or dislocations intersecting the space-charge region. In addition, voltage dependent values of resistance (R_i) were obtained from forward and reverse bias I-V characteristics by using Ohm's law for each temperature level.     

Electrical characterization of Au/n-GaN metal-semiconductor and Au/SiO2/n-GaN metal-insulator-semiconductor structures

In the present work, we have investigated the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of Au/SiO₂/n-GaN metal-insulator-semiconductor (MIS) Schottky diode and compared with Au/n-GaN metal-semiconductor (MS) Schottky diode. Calculations showed that the Schottky barrier height and ideality factor of the MS Schottky diode is 0.79 eV (I-V), 0.87 eV (C-V) and 1.45, respectively. It is observed that the Schottky barrier height increases to 0.86 eV (I-V), 0.99 eV (C-V) and ideality factor deceases to 1.3 for MIS diode. For the MS diode, the calculated doping concentration is 4.17 × 10¹⁷ cm⁻³. However, in the case of the MIS Schottky diode, the decrease in doping concentration is observed and the respective value is 2.08 × 10¹⁷ cm⁻³. The obtained carrier concentration of the MIS diode is reduced about 50% when compared to the MS diode. The interface state density as determined by Terman's method is found to be 3.79 × 10¹² and 3.41 × 10¹⁰ cm⁻² eV⁻¹ for the MS and MIS Schottky diodes, respectively. The calculated interface densities are 2.47 × 10¹¹ cm⁻² eV⁻¹, 3.35 × 10¹¹ cm⁻² eV⁻¹ and 3.5 × 10¹¹ cm⁻² eV⁻¹ for the sweep rates of 300, 450 and 600 mV/s from MOS C-V measurements for the MIS Schottky diode. The interface state density calculated from Terman's method is found to be increased with sweep rate. From the C-V measurement, it is noted that the decrease in the carrier concentration in MIS diodes as compared to MS diode may be due to the presence of oxide interfacial layer. DLTS measurements have also been performed on MIS Schottky diode and discussed.     

The studies of phase relation, microstructure, magnetic transition, magnetocaloric effect in (Gd1−xErx)5Si1.7Ge2.3 compounds

The phase relation, microstructure, Curie temperatures (T_C), magnetic transition, and magnetocaloric effect of (Gd_1−xEr_x)₅Si_1.7Ge_2.3 (x = 0, 0.05, 0.1, 0.15, and 0.2) compounds prepared by arc-melting and then annealing at 1523 K (3 h) using purity Gd (99.9 wt.%) are investigated. The results of XRD patterns and SEM show that the main phases in those samples are mono-clinic Gd₅Si₂Ge₂ type structure. With increase of Er content from x = 0 to 0.2, the values of magnetic transition temperatures (T_C) decrease linearly from 228.7 K to 135.3 K. But the (Gd_1−xEr_x)₅Si_1.7Ge_2.3 compounds display large magnetic entropy near their transition temperatures in a magnetic field of 0-2 T. The maximum magnetic entropy change in (Gd_1−xEr_x)₅Si_1.7Ge_2.3 compounds are 24.56, 14.56, 16.84, 14.20, and 13.22 J/kg K⁻¹ with x = 0, 0.05, 0.1, 0.15, and 0.2, respectively.     

Microstructure evolution of directionally solidified Ti-45Al-8.5Nb-(W, B, Y) alloys

Intermetallic Ti-45Al-8.5Nb-(W, B, Y) alloys were directionally solidified at constant growth rates (V) ranging from 10 to 400 μm/s under the temperature gradient G = 3.8 × 10³ K/m. Quenching was performed at the end of directional solidification (DS) experiments. Microstructure evolution was investigated by analyzing the microstructures formed at the quenching interfaces and in the DS regions. The primary dendritic arm spacing (λ) decreases with increasing growth rate according to the relationship λ ∝ V^−0.36. Both the width of columnar grain (λw) and the interlamellar spacing (λ_s) decrease with increasing growth rate according to the relationships λw∝V−1.13 and λ_s ∝ V^−0.32, respectively. Lamellar microstructure initially disappears from the dendrites at the growth rate of 100 μm/s and subsequently from the interdendritic regions when the growth rate is up to 200 μm/s. The B2 particles can precipitate in the interdendritic regions.     

Synthesis of the pyrrolo[3,2-b]pyrrole-based copolymer with enhanced open circuit voltage

A new accepter unit, pyrrolo[3,2-b]pyrrole-2,5-dione, was prepared and utilized for the synthesis of the conjugated polymer containing electron donor–acceptor pair for OPVs. Pyrrolo[3,2-b]pyrrole-2,5-dione unit, regioisomer of the known pyrrolo[3,4-c]pyrrole-1,4-dione, is originated from the structure of stable synthetic pigment. The new conjugated polymer with pyrrolo[3,2-b]pyrrole-2,5-dione, thiophene and carbazole was synthesized using Suzuki polymerization to generate P1. The solid thin film of P1 shows absorption band with maximum peaks at 374 and 548 nm, and the absorption onset at 679 nm, corresponding to band gap of 1.83 eV. The field-effect hole mobility of P1 is 2.2 × 10⁻⁵ cm²/Vs. The device based on the polymer:PCBM (1:2) blend without thermal treatment showed a V_OC of 0.82 V, a J_SC of 6.28 mA/cm², and an FF of 0.39, giving a PCE of 2.00%.     

Studies on the power factor of (Ba,Sr)Co2+xRu4−xO11 compounds

We have prepared polycrystalline single-phase ACo_2+xRu_4−xO₁₁ (A = Sr, Ba; 0 ≤ x ≤ 0.5) using the ceramic method and we have studied their structure, electrical resistivity and Seebeck coefficient, in order to estimate their power factor (P.F.). These layered compounds show values of electrical resistivity of the order of 10⁻⁵ Ωm and their Seebeck coefficients are positive and range from 1 μV K⁻¹ (T = 100 K) to 20 μV K⁻¹ (T = 450 K). The maximum power factor at room temperature is displayed by BaCo₂Ru₄O₁₁ (P.F.: 0.20 μW K⁻² cm⁻¹), value that is comparable to that shown by compounds such as SrRuO₃ and Sr₆Co₅O₁₅.     

Transport properties of sealed MgB2/Fe/Ni multifilamentary wires heat treated in air

Ni sheathed multifilamentary MgB₂ wires with Fe barrier and Cu stabilizer were prepared by the in situ Powder-In-Tube (PIT) method. After rolling, the ends of the wires were sealed by a simple capping technique and the wires were directly heat treated in air, without vacuum or any inert atmosphere. The quality of the wires was assessed by analysing the phase assemblage and measurement of superconducting properties such as R-T, J_C-T and J_C-H. Phase analysis revealed that only traces of MgO was formed in the superconductor core. Typical multifilamentary wires prepared by this method showed a T_C ≈ 38.5 K and ΔT_C ≈ 1 K and J_C of the order of 10⁵ A/cm² at 6 K (0 T) and 10⁴ A/cm² at 4.2 K (6 T) respectively. These values are quite comparable with the values obtained for wires heat treated in inert atmosphere.     

Synthesis and magnetic properties of nickel nanoparticles deposited on the silicon nanowires

Nickel (Ni) nanoparticles with sizes of ∼35 nm were deposited on the surface of silicon nanowires (SiNWs) by electroless plating technique. The magnetic properties of Ni/SiNWs were investigated. The blocking temperature (T_B) of 370 K was obtained and confirmed by field-cooled (FC) and zero-field-cooled (ZFC) plots. The M-H hysteresis loops from 5 K to 400 K were measured. The saturation magnetization value was ∼4.5 emu/g and the coercivity was ∼375.3 Oe for the loop at 5 K, respectively. While for the loop at 400 K, these values were of ∼2.6 emu/g and ∼33.3 Oe, respectively. The temperature dependence of coercivity followed by the relation H_C(T) = H_C0[1 − (T/T_B)^1/2], indicating a superparamagnetic behavior. The magnetization of superparamagnetic grains in a magnetic field H was better described by Langevin function at 400 K. These novel magnetic properties of Ni/SiNWs were possibly attributed to the paramagnetic defects on the surface of SiNWs.     

Coexistence of room temperature ferroelectricity and ferrimagnetism in multiferroic BiFeO3-Bi0.5Na0.5TiO3 solid solution

The structure, ferroelectric and magnetic properties of (1 − x)BiFeO₃-xBi_0.5Na_0.5TiO₃ (x = 0.37) solid solution fabricated by a sol-gel method have been investigated. X-ray diffraction and Raman spectroscopy measurements show a single-phase perovskite structure with no impurities identified. Compared with pure BiFeO₃, the coexistence of ferroelectricity and ferrimagnetism have been observed at room temperature for the solution with remnant polarization P_r = 1.41 μC/cm² and remnant magnetization M_r = 0.054 emu/g. Importantly, a magnetic transition from ferrimagnetic (FM) ordering to paramagnetic (PM) state is observed, with Curie temperature T_C ∼ 330 K, being explained in terms of the suppression of cycloid spin configuration by the structural distortion.     

Electrical characterization of a-Si:H(n)/c-Si(p) structure

In this study, n-type hydrogenated amorphous silicon (a-Si:H) was fabricated on p-type crystalline silicon (c-Si) substrates to obtain heterojunction diodes. The amorphous films were obtained by the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. Temperature dependent current-voltage (I-V-T) measurements and investigation of the dc current injection mechanism of a-Si:H(n)/c-Si(p) device structure have been performed. The series resistance (4.6-8.2 Ω) values displayed nearly temperature independent behavior and the ideality factor varied between 2.7 and 1.6 in the temperature range 100-320 K. The forward bias I-V-T characteristics of c-Si/a-Si:H heterojunctions are found to behave like the Schottky junctions where carrier injection is especially influenced by the carrier generation-recombination in the junction interface formed on the amorphous side. The temperature dependent ideality factor behavior shows that tunneling enhanced recombination is valid rather than thermionic emission theory. In the frame of this model, characteristic tunneling energy and characteristic temperature are found to be 9 meV and 1900 K, respectively. It is concluded that fabricate n-type hydrogenated amorphous silicon is a preferable semiconductor material layer with low interface state density because the temperature dependent interface state density calculations give values of the order of 10¹⁴ eV⁻¹ cm⁻².     

Near room temperature magnetic entropy changes in as-cast Gd100−xMnx (x = 0, 5, 10, 15, and 20 at.%) alloys

A series of Gd_100−xMn_x (x = 0, 5, 10, 15, and 20 at.%) alloys were prepared by arc-melting. The Curie temperature (T_C) associated with the ferromagnetic-paramagnetic transitions, derived from M-T curves, show decrease in T_C for as-cast alloys (∼279 K) as compared to as-cast Gd (∼292 K). No appreciable decrease in the |ΔS_M|_max values ∼4.6 J/kg K (0-2 T) and ∼8.6 J/kg K (0-5 T) were observed upon alloying Gd with Mn up to x ≤ 15 at.%. Refrigerant capacity (q) showed negligible variation ∼195 J/kg (0-2 T) and ∼450 J/kg (0-5 T) with increasing Mn (up to x ≤ 15 at.%) content. Similar values of |ΔS_M|_max and q coupled with ∼13 K decrease in T_C for as-cast Gd_100−xMn_x (0 ≤ x ≤ 15) alloys as compared to Gd, suggests expansion of working temperature region of Gd upon alloying with Mn up to 15 at.%. Low cost, adjustable T_C, favorable magnetocaloric properties make Gd_100−xMn_x alloys potential candidates as second-order transition based magnetic refrigerants for near room temperature air-conditioning and magnetic refrigeration.     

Electrical, magnetic, and Hall properties of AlxCoCrFeNi high-entropy alloys

This investigation explores the electrical and magnetic properties of as-cast, -homogenized, and -deformed Al_xCoCrFeNi (C-x, H-x, and D-x, respectively) alloys at various temperatures from 4.2 to 300 K. Experimental results reveal that carrier density of the alloys is of 10^22-23 cm⁻³. H-x has a carrier mobility of 0.40-2.61 cm² V⁻¹ s⁻¹. The residual electrical resistivity of the alloys varies from 100 to 220 μΩ cm. The temperature coefficient of resistivity (TCR) of H-2.00 is small (82.5 ppm/K). Therefore, defects in the lattice dominate electrical transportation. Some compositions exhibit Kondo-like behavior. At 300 K, H-0.50, H-1.25, and H-2.00 are ferromagnetic, while H-0.00, H-0.25, and H-0.75 are paramagnetic. Al and AlNi-rich phases reduce the ferromagnetism of single FCC and single BCC H-x, respectively. Spin glass behavior of some compositions is also observed. Alloys H-x are of the hole-like carrier type, and ferromagnetic H-x exhibits an anomalous Hall effect (AHE).     

The current–voltage and capacitance–voltage characteristics of molecularly modified β-carotene/n-type Si junction structure with fluorescein sodium salt

β-Carotene–FSS organic semiconductor/n-type Si structure has been characterized by current–voltage and capacitance–voltage methods. A deviation in I–V characteristic of the diode is observed due to effect of series resistance and interfacial layer. Cheung's functions were used to calculate diode parameters. The ideality factor, series resistance and barrier height values of the diode are n = 1.77, R_s = 10.32 (10.39) kΩ and 0.78 eV. The obtained ideality factor suggests that Au/β-carotene–FSS/n-Si Schottky diode has a metal–SiO₂ oxide layer plus organic layer–semiconductor (MIOS) configuration. The capacitance–voltage characterizations of Au/β-carotene–FSS/n-Si diode at different temperatures were performed. The capacitance of the diode changes with temperature. The barrier height and ideality factor obtained from C–V curves are 0.67 eV and 1.68. The interface density properties of the diode are analyzed and the shape of the density distribution of the interface states is in the range of E_c −0.49 to −0.62 eV. It is evaluated that the FSS organic layer controls electrical charge transport properties of Au/β-carotene/n-Si diode by excluding effects of the β-carotene and SiO₂ residual oxides on the hybrid diode.     

Electrical properties of Al/conducting polymer (P2ClAn)/p-Si/Al contacts

Al/P2ClAn/p-Si/Al structure was obtained by the evaporation of the polymer P2ClAn on the front surface of p-type silicon substrate. The P2ClAn emeraldine salt was chemically synthesized by using propionic (C₂H₅COOH) acid. The current–voltage (I–V) characteristic of the structure was measured at room temperature. The capacitance–voltage–frequency (C–V–f) in terms of interface states over the frequency range of 10 kHz to 3 MHz has been investigated. The capacitance has decreased with increasing frequency, due to the interface states distribution. From the forward bias I–V plot for the sample, the ideality factor (n) and zero-bias barrier height (Φ_bp,0) were obtained as 4.84 and 0.787 eV, respectively. Under forward bias, the high value of the ideality factor and the dispersion in capacitance could be due to the interface state distribution, the interfacial insulator layer, the conducting polymer on the interface and inhomogeneity of the barrier height. The energy distributions and the relaxation times of the interface states were determined in the energy range of (0.387 − E_v) to (0.787 − E_v) eV.     

Ferromagnetism in ZnTe:Cr film grown on Si(1 0 0)

Zn_1−xCr_xTe (x = 0.0 and 0.05) films were grown on Si(1 0 0) substrate by using thermal evaporation method. The structure of the films was investigated by X-ray diffraction and it showed the formation of ZnCrTe phase with an amorphous background, which indicated poor crystallinity. Composition analysis by XPS disclosed the presence of antiferromagnetic Cr₂O₃ and Cr precipitates. Magnetic domains were observed by using magnetic force microscopy at ambient temperature and the result showed anisotropic domains with an average size of 3.5 nm. Magnetic field dependence of magnetic moment measurements showed obvious hysteresis loop with a coercive field of 121 Oe at 300 K. Temperature dependence of magnetic moment showed short-range ferromagnetic order. The Curie temperature was estimated to be 354.5 K.     

Moderate temperature and high-speed synthesis of α-Al2O3 films by laser chemical vapor deposition using Nd:YAG laser

Al₂O₃ films were prepared at deposition temperatures (T_dep) from 980 to 1230 K by laser chemical vapor deposition (LCVD) using the continuous wave of a Nd:YAG laser with laser power (P_L) up to 260 W. γ-Al₂O₃ films were obtained at T_dep < 1100 K, whereas α-Al₂O₃ films were obtained at T_dep > 1100 K. γ-Al₂O₃ films were morphologically characterized by a cone-like structure, while α-Al₂O₃ films had hexagonal faceted grains. The highest deposition rate (R_dep) of γ-Al₂O₃ film was 570 μm h^− 1, while that of α-Al₂O₃ film was 250 μm h^− 1. α-Al₂O₃ films in a single phase were obtained at 170 K lower in T_dep and 100 times higher in R_dep than those by conventional thermal CVD.     

Hydrogen embrittlement of duplex stainless steel under cathodic protection in acidic artificial sea water in the presence of sulphide ions

By slow strain rate technique, hydrogen embrittlement (HE) of a 2205 duplex stainless steel was studied in deaerated acidic (pH 6.5) artificial sea water, in the absence and in presence of sulphide ions (1-30 ppm). Strain rate tests (1 × 10⁻⁶ s⁻¹) were performed on specimens polarized at −0.9; −1.0 and −1.2 V_SCE at 25 ± 0.1 °C. HE was evaluated by R, the ratio between the % elongation to fracture in the aggressive solution and in air.Duplex stainless steel were subjected to HE in acidic artificial sea water at −0.9 V_SCE. HE increased at −1.0 V_SCE but it was reduced at −1.2 V_SCE. This decrease was attributed to the influence of a calcareous deposit.Sulphide ions at 1 ppm were sufficient to stimulate HE of duplex stainless steel. The higher the sulphide amount and the more negative the cathodic potential, the higher HE was. In the presence of S²⁻, the shielding effect of the calcareous deposit was not evident.     

Effect of the sintering temperature on the properties of nanocrystalline Ca1−xSmxMnO3 (0 ≤ x ≤ 0.4) powders

Nanocrystalline Ca_1−xSm_xMnO₃ (0 ≤ x ≤ 0.4) manganites were prepared by a soft chemical method (Pechini method) followed by auto-combustion and sintering in air at 1073 or 1473 K. Single-phase powders with general composition Ca_1−xSm_xMnO₃ were obtained after 18 h annealing. The particle and grain sizes of the substituted Sm-manganites did not exhibit variation with samarium content, but increase with increasing the sintering temperature. All manganites show two active IR vibrational modes near 400 and 600 cm⁻¹ characteristic of the BO₆ octahedron vibrations.For the samples sintered at T_s = 1473 K, the partial substitution of calcium by samarium in the CaMnO₃ phase induces a marked decrease in the electrical resistivity, in the temperature range of 300-900 K, and at the same time a metal-to-insulator transition occurs; for T_s = 1073 K all the samples present semiconductor behaviour. With the increase of the annealing temperature the grain size increases and a metal-semiconductor transition appears. The results can be ascribed to the Mn⁴⁺/Mn³⁺ ratio and particle grain size. The effects of particle size on the electrical properties can be attributed to the domain status, changes in the Mn-O-Mn bond angle and Mn-O bond length.