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.     

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.     

Effects of post-annealing on Schottky contacts of Pt/ZnO films toward UV photodetector

The Schottky contact of Pt/ZnO was formed by depositing ZnO films oriented along c-axis by pulsed-laser deposition on Pt/Ti buffer layer supported by SiO₂/Si substrate. Effects of the post-annealing on the crystallinity, uniformity and native defects of ZnO film as well as Schottky contacts of Pt/ZnO films were investigated. Results show that the annealing can improve the crystallinity of ZnO film, suppress the native defects, and enhance the performance of Pt/ZnO Schottky contacts dramatically. The best Schottky diode shows the largest barrier height of 0.8 eV with reverse leakage current of 1.5 × 10⁻⁵ A/cm². The zero-biased photodetector based on the best Schottky diode possesses responsivity of 0.265 A/W at 378 nm, fast photo-response component with rise time of 10 ns and fall time of 17 ns. This report demonstrates possibility of ZnO films/Pt hetero-junction with large area Schottky contact, and establishes the potential of this material for use in UV photodetector devices.     

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.     

Temperature dependent admittance spectroscopy of GaAs/AlGaAs single-quantum-well laser diodes (SQWLDs)

In this study, the main electrical parameters, such as doping concentration (N_D), barrier height (Φ_CV), depletion layer width (W_D), series resistance (R_s) and Fermi energy level (E_F), of GaAs/Al_xGa_1−xAs single quantum well (SQW) laser diodes were investigated using the admittance spectroscopy (C-V and G/ω-V) method in the temperature range of 80-360 K. The reverse bias C⁻² vs. V plots gives a straight line in a wide voltage region, especially in weak inversion region. The values of Φ_CV at the absolute temperature (T = 0 K) and the temperature coefficient (α) of barrier height were found as 1.22 eV and −8.65 × 10⁻⁴ eV/K, respectively. This value of α is in a close agreement with α of GaAs band gap (−5.45 × 10⁻⁴ eV/K). Experimental results show that the capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the diode are affected by not only temperature but also R_s. The capacitance-voltage-temperature (C-V-T) and conductance-voltage-temperature (G/ω-V-T) characteristics confirmed that temperature and R_s of the diode have effects on the electronic parameters in SQW laser diodes.     

Effects of illumination on capacitance characteristics of Au/3C-SiC/p-Si/Al diode

Au/3C-SiC/p-Si/Al Schottky barrier diode was prepared using atmospheric pressure chemical vapor deposition technique. The device parameters such as barrier height, ideality factor, and series resistance were calculated using current-voltage characteristics, and were found to be 0.44 eV, 1.55, and 1.02 × 10⁴ Ω, respectively. The photocapacitive properties of the diode were studied under various illumination intensities. The transient photocapacitance measurements indicate that the capacitance of the Au/3C-SiC/p-Si/Al Schottky diode is very sensitive to illumination. The photocapacitance of the diode increases with increase in illumination intensity. The increase in photocapacitance with increase in illumination intensity suggests that these devices could be utilized as a photocapacitive sensor for optical sensors.     

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.     

Fabrication and characterization of ITO thin films on heat-resistant transparent flexible clay films

Transparent conductive indium tin oxide (ITO) thin films were deposited on transparent flexible clay films with heat resistant and high gas barrier properties by rf magnetron sputtering. The electrical, structural, and optical properties of these films were examined as a function of deposition temperature. A lowest resistivity of 4.2 × 10^− 4 Ωcm and an average transmittance more than 90% in the visible region were obtained for the ITO thin films fabricated at deposition temperatures more than 300 °C. It was found that ITO thin films with low resistivity and high transparency can be achieved on transparent flexible clay film using conventional rf magnetron sputtering at high temperature, those characteristics are comparable to those of ITO thin films deposited on a glass substrate.     

Investigating behaviors of H in a W single crystal by first-principles: From solubility to interaction with vacancy

We have investigated structure and solubility of H, as well as H-vacancy interaction in tungsten (W) single crystal employing a first-principles method. Single H atom is shown to be energetically favorable sitting at the tetrahedral interstitial site (TIS). The solubility of H is estimated in W according to the Sieverts’ law. We found that the solution concentrations are 2.3 × 10⁻¹⁰ and 1.8 × 10⁻⁷ at the typical temperatures of 600 K and 1000 K, respectively. The calculated results are basically consistent with the experiments. The vacancy can be found to play a key role on the trapping of H in W. There exists a very strong binding between single H and vacancy with the binding energy of 1.18 eV. With the H atoms added, the H_nV complexes can be easily formed in the vacancy. A monovacancy is shown to be capable of trapping as many as 7 H atoms. Kinetically, we show that the H jumps into the vacancy from the first nearest neighboring TIS into vacancy with a much reduced barrier of 0.02 eV, which indicates a down-hill “drift” diffusion of H towards vacancy. The physical mechanism underlying H assisted vacancy formation is originated from that H atoms can stimulate the formation and growth of vacancy or void by binding with vacancy to decrease the effective formation energy of vacancy in W.     

Analysis of electrical and photoelectrical properties of ZnO/p-InP heterojunction

A ZnO/p-InP heterojunction has been fabricated by dc sputtering of ZnO on p-InP. It has been observed that the device has a good rectification. The electrical properties of the device such as ideality factor, barrier height, series resistance have been calculated using its current-voltage (I-V) measurements between 300 and 380 K with 20 K intervals. The short current density (J_sc) and open circuit voltage (V_oc) parameters have been determined between 40 and 100 mW/cm². The photovoltaic parameters of the device have been also determined under 100 mW/cm² and AM1.5 illumination condition.     

Thermal expansion and lattice parameters of shaped metal deposited Ti-6Al-4V

Thermal expansion and lattice parameters are investigated up to 1100 °C for Ti-6Al-4V components, fabricated by shaped metal deposition. This is a novel additive layer manufacturing technique where near net-shape components are built by tungsten inert gas welding.The as-fabricated SMD Ti-6Al-4V components exhibit a constant coefficient of thermal expansion of 1.17 × 10⁻⁵ K⁻¹ during heating up to 1100 °C, not reflecting the α to β phase transformation. During cooling a stalling of the contraction is observed starting at the β transus temperature. These high temperature experiments denude the α phase of V and enrich the β phase.The development of the lattice parameters in dependence on temperature are observed with high temperature X-ray diffraction. The unit cell volumes derived from these parameters are at room temperature larger for the α than for the β phase. With increasing temperature the unit cell volume of the β phase increases stronger than the one of the α phase resulting in a similar unit cell volume at the β transus temperature.These observations are interpreted as an indication for as-fabricated the SMD components being in a non-equilibrium state and reaching equilibrium during the slow heating and cooling during of the two different high temperature experiments.     

Structural, optical and electrical properties of CuIn5S8 thin films grown by thermal evaporation method

Stoichiometric compound of copper indium sulfur (CuIn₅S₈) was synthesized by direct reaction of high purity elemental copper, indium and sulfur in an evacuated quartz tube. The phase structure of the synthesized material revealed the cubic spinel structure. The lattice parameter (a) of single crystals was calculated to be 10.667 Å. Thin films of CuIn₅S₈ were deposited onto glass substrates under the pressure of 10⁻⁶ Torr using thermal evaporation technique. CuIn₅S₈ thin films were then thermally annealed in air from 100 to 300 °C for 2 h. The effects of thermal annealing on their physico-chemical properties were investigated using X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM), optical transmission and hot probe method. XRD studies of CuIn₅S₈ thin films showed that as-deposited films were amorphous in nature and transformed into polycrystalline spinel structure with strong preferred orientation along the (3 1 1) plane after the annealing at 200 °C. The composition is greatly affected by thermal treatment. From the optical transmission and reflection, an important absorption coefficient exceeds 10⁴ cm⁻¹ was found. As increasing the annealing temperature, the optical energy band gap decreases from 1.83 eV for the as-deposited films to 1.43 eV for the annealed films at 300 °C. It was found that CuIn₅S₈ thin film is an n-type semiconductor at 300 °C.     

Strong correlation between structural, magnetic and transport properties of non-stoichiometric Sr2FexMo2−xO6 (0.8 ≤ x ≤ 1.5) double perovskites

Sr₂Fe_xMo_2−xO₆ (x = 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 and 1.5 wt.%) (SFMO) double perovskite oxides of different compositions have been prepared by sol-gel method. These materials were subjected to X-ray diffraction and found that crystal structure changes from tetragonal to cubic around x = 1.2 wt.%. Lattice parameters and unit cell volume have been calculated using X-ray diffraction data. Magnetization studies have been carried out using Vibrating Sample Magnetometer ranging from −15 kOe to +15 kOe and saturation magnetization (M_s) has been determined. Electrical resistivity and magnetoresistance studies have been carried out in the magnetic field range of −40 kOe to +40 kOe keeping the temperature constant at 5, 150 and 300 K using standard four-probe method. Resistivity studies have also been carried out in the temperature ranging from 5 to 300 K keeping the magnetic field constant at 0, 10, 20 and 40 kOe. Maximum degree of Fe/Mo ordering (η_max) of SFMO has been calculated and compared with magnetic and transport properties. It has been found that there is a strong correlation between 3 parameters η_max, M_s and MR (%), i.e. all of them show a maximum at x = 1.0 wt.% and decreases as x deviates from 1.0 in SFMO. It has been also found that there is a different resistivity behavior between x ≤ 1.2 wt.% and x > 1.2 wt.% samples of SFMO. Semiconductor metal transition temperature was found to be maximum at x = 1.0 wt.%.     

Temperature- and excitation-dependent photoluminescence in TlGaSeS layered crystals

Photoluminescence (PL) spectra of TlGaSeS layered single crystals have been studied in the wavelength region of 695-1010 nm and in the temperature range of 20-56 K. Two PL bands centered at 773 (1.605 eV, A-band) and 989 nm (1.254 eV, B-band) were observed at T = 20 K. Variations of both bands have been investigated as a function of excitation laser intensity in the range from 4.2 to 111.4 mW cm⁻². These bands are attributed to recombination of charge carriers through donor-acceptor pairs located in the band gap of the crystal. Radiative transitions from deep donor levels located at 0.721 and 1.069 eV below the bottom of conduction band to shallow acceptor levels located at 0.008 and 0.011 eV above the top of the valence band are suggested to be responsible for the observed A- and B-bands in the PL spectra, respectively.     

Thermoelectric properties of Cu1−xPtxFeO2 (0.0 ≤ x ≤ 0.05) delafossite-type transition oxide

The samples of Cu_1−xPt_xFeO₂ (0 ≤ x ≤ 0.05) delafossite were synthesized by solid state reaction method for studying thermoelectric properties. The properties of Seebeck coefficient, electrical conductivity and thermal conductivity were measured in the high temperature ranging from 300 to 960 K. The results of Seebeck coefficient, electrical conductivity and power factor were increased with increasing Pt substitution and temperature. The thermal conductivity was decreased from 5.8 to 3.5 W/mK with increasing the temperature from 300 to 960 K. An important results, the highest value of power factor and ZT is 2.0 × 10⁻⁴ W/mK² and 0.05, respectively, for x = 0.05 at 960 K.     

Solvent extraction of molybdenum blue from alkaline leaching solution of the Ni-Mo ore

Molybdenum in the Ni-Mo ore was leached by air oxidation in an alkaline solution. Due to the high concentrations of SO₄²⁻, S₂O₃²⁻, SO₃²⁻ and AsO₄³⁻ in the solution, it was difficult to efficiently extract Mo by chemical precipitation or ion exchange process. So the extraction of Mo from the solution with the mixture of tertiary amine (N-235) and secondary caprylic alcohol dissolved in kerosene was investigated. The effects of several process parameters such as extractant concentration, feed solution pH, O/A ratio, temperature of extraction, and contact time were studied. Results proved that the extraction efficiency of Mo was 99.4% at pH 3, time 2 min and O/A ratio 1:4 with 15 v% N-235. Stripping of Mo with a 15 m% ammonia solution was essentially completed (99.9%) in a single stage at an O/A ratio of 3. Comparison of the chemical oxygen demand (COD) concentration of the feed solution (12,400 mg/L) and raffinate (8600 mg/L) indicated that the separation of Mo and reductive substances, such as S₂O₃²⁻ and SO₃²⁻, was achieved after solvent extraction. The Mo concentration in the strip liquor obtained in a single stage can be increased by contacting a new loaded organic phase. After repeated stripping, the concentration of Mo, As, P, W and V in the strip liquor were 125.82 g/L, 15.63 g/L, 0.73 g/L, 0.09 g/L, and 0.074 g/L respectively.     

Optical spectra and excited state relaxation dynamics of Nd in CaF2 single crystal

Nd-doped CaF₂ crystal with high optical quality was obtained by a temperature gradient technique (TGT). Energies of the crystal field levels of Nd³⁺ multiplets relevant to laser operation were determined based on optical spectra recorded at T = 10 K. Room temperature absorption spectra were analyzed in the framework of the Judd-Ofelt theory to calculate radiative transition rates and luminescence branching ratios for the ⁴F_3/2 level. The ⁴F_3/2 radiative lifetime was calculated to be 1295 μs whereas a monotonous decrease of the ⁴F_3/2 luminescence lifetime value from 1.45 ms to 0.9 ms was observed when the temperature increased from 10 K to 300 K. The stimulated emission cross-section of 1.48 × 10⁻²⁰ cm² at 1061 nm was determined using the Fuchtbauer-Ladenburg relation. All the results showed that Nd:CaF₂ would be a promising gain media in solid-state lasers.     

Aluminum alloy pistons reinforced with SiC fabricated by centrifugal casting

Hypereutectic Al-Si alloy-based composite pistons reinforced with SiC particles locally at the head were fabricated by centrifugal casting. The effects of various technique parameters, i.e., the slurry temperature of the alloy, the mold temperature and the rotation speed of the mold, on the particle segregation were investigated, and the macromorphologies and microstructures of pistons were observed. The mechanical properties, such as hardness and wear resistance along the axis of the piston and the thermal expansion coefficient at the piston head, were measured. The results showed that, (1) centrifugal casting can be used as a new and effective method in manufacturing pistons, and reasonable parameters were 850 °C, 600 °C and 800 rpm for the slurry temperature of the alloy, the mold temperature and the rotation speed of the mold, respectively; (2) the hardness values of pistons fabricated by centrifugal casting gradually increased from the piston skirt to the piston head, and the average hardness value in piston heads was improved by 23.7HRB over that of pistons fabricated by gravity permanent mold casting; (3) the piston heads showed excellent wear resistance, and the wear rate of piston heads decreased by 70.3% over that of the piston fabricated by gravity permanent mold casting; and (4) the average linear expansion coefficient of the piston head was 15.3 × 10⁻⁶ K⁻¹ and decreased by 23.1% over that of pistons fabricated by gravity permanent mold casting.     

Thermoelectric properties of Sc- and Y-doped Mg2Si prepared by field-activated and pressure-assisted reactive sintering

Sc- and Y-doped-Mg₂Si samples were reactively sintered by the field-activated and pressure-assisted synthesis (FAPAS) method. The incorporation of these rare-earth elements in this silicide resulted in an n-type semiconductor. The addition of Sc and Y had no discernable effect on the lattice constant of Mg₂Si. The average grain size of the Y-doped Mg₂Si was about 2 μm, which was smaller than that of the sintered pure Mg₂Si. The power factor of samples doped with 2500 ppm Sc was consistently higher than that of pure Mg₂Si in the temperature range of 300-550 K. Similarly, the power factor of 2000 ppm Y doped Mg₂Si samples was higher than that of pure Mg₂Si over the temperature range of 300-675 K; the highest value being about 2.2 × 10⁻³ W m⁻¹ k⁻² at 468 K. This value is about two times that of the undoped Mg₂Si at the same temperature. The thermal conductivity of Mg₂Si doped with 2000 ppm Y was 80% of that of pure Mg₂Si. The highest figure of merit (ZT) for the Y doped (2000 ppm) samples was 0.23 at 600 K which was higher by a factor of 1.6 than the corresponding value of pure Mg₂Si at the same temperature. The results demonstrate the benefits of doping of Mg₂Si with Sc and Y in enhancing its thermoelectric properties.