The electrical characterization of Zn(Phen)q/p-type Si/Al diode with interfacial layer by current–voltage characteristics

The current–voltage characteristics of Zinc (II) [(8-hydroxyquinoline)(1,10-phenanthroline)] complex (Zn(phen)q)/p-type Si/Al diode with interfacial layer have been investigated. The barrier height and ideality factor of the diode were found to be 0.71 eV and 2.05. Zn(phen)q/p-type Si/Al diode shows a metal–insulator–semiconductor structure resulted from presence of series resistance and an interfacial layer. The n and φ_B values obtained the presence of interfacial layer are 1.02 and 0.70 eV, respectively. The effect of series resistance was evaluated using a method developed by Cheung. The R_s and n values were determined from the d ln(I)/dV plot and were found to be 30.43 kΩ and 2.16, respectively. The barrier height and R_s values were calculated from the H(I)–I plot and were found to be 0.70 eV and 30.99 kΩ. The density of the interface states of the Zn(phen)q/p-type Si/Al diode was calculated and was found to be an order of 10¹³ eV⁻¹ cm⁻².     

Electrical conductivity, optical and metal–semiconductor contact properties of organic semiconductor based on MEH-PPV/fullerene blend

The electrical conductivity, optical and metal–semiconductor contact properties of the MEH-PPV:C₇₀ organic semiconductor have been investigated. The electrical conductivity results show that the MEH-PPV:C₇₀ film is an organic semiconductor. The optical band gap of the film was found to be 2.06 eV and the fundamental absorption edge in the film is formed by the direct allowed transitions. The refractive index dispersion curve of the film obeys the single oscillator model and E_d and E_o dispersion parameters were found to be 10.61 and 3.89 eV, respectively. The electrical characterization of the ITO/MEH-PPV:C₇₀ diode have been investigated by current–voltage characteristics. ITO/MEH-PPV:C₇₀ diode indicates a non-ideal current–voltage behavior with ideality factor n (2.50) and barrier height φ_B (0.90 eV) values.     

The dependence of I–V and C–V characteristics on temperature in the H-terminated Pb/p-Si(1 0 0) Schottky barrier diodes

The current–voltage (I–V) and capacitance–voltage (C–V) characteristics of H-terminated Pb/p-Si/Al contacts fabricated by us have been measured in the temperature range of 77–300 K. The experimental values of the barrier height (BH) Φ_bo and the ideality factor n for the device range from 0.674 and 1.072 eV (at 300 K) to 0.352 and 2.452 eV (at 77 K), respectively. The ideality factors become larger with lowering temperature while the barrier height decreases. The Φ_bo(n) plot shows a linear dependence in the temperature range of 77–300 K that can be explained by the barrier inhomogeneity at the metal/semiconductor interface. The extrapolation of the linear Φ_bo(n) plot to n = 1 has given a homogeneous barrier height of approximately 0.713 eV for the Pb/p-Si(1 0 0) contact. A Φ_bo versus 1/T plot was drawn to obtain evidence of a Gaussian distribution of the BHs, and values of and σ_s = 80.5 mV for the mean BH and zero-bias standard deviation have been obtained from this plot, respectively. Then, a modified versus 1/T plot gives and A^* as 0.828 eV and 54.89 A/cm² K², respectively. Furthermore, an average value of −0.687 meV/K for the temperature coefficient has been obtained, the value of −0.687 meV/K for hydrogen terminated p-type Si differs from those given for p-type Si without hydrogen termination in the literature.     

Analysis of frequency-dependent series resistance and interface states of In/SiO2/p-Si (MIS) structures

In this work, the investigation of the interface state density and series resistance from capacitance–voltage (C–V) and conductance–voltage (G/ω−V) characteristics in In/SiO₂/p-Si metal–insulator–semiconductor (MIS) structures with thin interfacial insulator layer have been reported. The thickness of SiO₂ film obtained from the measurement of the oxide capacitance corrected for series resistance in the strong accumulation region is 220 Å. The forward and reverse bias C–V and G/ω−V characteristics of MIS structures have been studied at the frequency range 30 kHz–1 MHz at room temperature. The frequency dispersion in capacitance and conductance can be interpreted in terms of the series resistance (R_s) and interface state density (D_it) values. Both the series resistance R_s and density of interface states D_it are strongly frequency-dependent and decrease with increasing frequency. The distribution profile of R_s–V gives a peak at low frequencies in the depletion region and disappears with increasing frequency. Experimental results show that the interfacial polarization contributes to the improvement of the dielectric properties of In/SiO₂/p-Si MIS structures. The interface state density value of In/SiO₂/p-Si MIS diode calculated at strong accumulation region is 1.11×10¹² eV⁻¹ cm⁻² at 1 MHz. It is found that the calculated value of D_it (≈10¹² eV⁻¹ cm⁻²) is not high enough to pin the Fermi level of the Si substrate disrupting the device operation.     

Structural and optical properties of thermally evaporated Bi2Te3 films

Bi₂Te₃ films were prepared by thermal evaporation technique. X-ray diffraction analysis for as-deposited and annealed films in vacuum at 150 °C were polycrystalline with rhombohedral structure. The crystallite size is found to increase as the film thickness increases and has values in the range 67–162 nm. The optical constants (the refractive index, n, and absorption index, k) were determined using transmittance and reflectance data in the spectral range 2.5–10 μm for Bi₂Te₃ films with different thicknesses (25–99.5 nm). Both n and k are independent on the film thickness in the investigated range. It was also found that Bi₂Te₃ is a high refractive index material (n has values of 4.7–8.8 in the wavelength range 2.5–10 μm). The allowed optical transitions were found to be direct optical transitions with energy gap  eV. The optical conductivities σ₁ = ƒ(hν) and σ₂ = f(hν) show distinct peaks at about 0.13 and 0.3 eV, respectively. These two peaks can be attributed to optical interband transitions.     

Effect of oxide thickness on the capacitance and conductance characteristics of MOS structures

In this work, the investigation of the interface states density and series resistance from capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics in Au/SnO₂/n-Si (MOS) structures prepared at various SnO₂ layer thicknesses by spray deposition technique have been reported. It is fabricated five samples depending on deposition time. The thicknesses of SnO₂ films obtained from the measurement of the oxide capacitance in the strong accumulation region for MOS Schottky diodes are 37, 79, 274, 401, and 446 Å, for D1, D2, D3, D4, and D5 samples, respectively. The C–V and G–V measurements of Au/SnO₂/n-Si MOS structures are performed in the voltage range from −6 to +10 V and the frequency range from 500 Hz to 10 MHz at room temperature. It is observed that peaks in the forward C–V characteristics appeared because of the series resistance. It has been seen that the value of the series resistance R_s of samples D1 (47 Ω), D2 (64 Ω), D3 (98 Ω), D4 (151 Ω), and D5 (163 Ω) increases with increasing the oxide layer thickness. The interface state density D_it ranges from 2.40×10¹³ cm⁻² eV⁻¹ for D1 sample to 2.73×10¹² cm⁻² eV⁻¹ for D5 sample and increases with increasing the oxide layer thickness.     

Structural study and magnetoresistance effect of epitaxial La0.67Sr0.33MnO3–δ and Pr0.7Ca0.3MnO3−δ multilayer films

La_0.67Sr_0.33MnO_3−δ (LSMO) and Pr_0.7Ca_0.3MnO_3−δ (PCMO) multilayer epitaxial films, which were fabricated with different LSMO and PCMO layer thickness on LaAlO₃ single crystal substrates of (0 0 1) orientation by a direct current magnetron sputtering technique, were studied further, after the structure, magnetoresistance effect and magnetic properties of LSMO/PCMO/LSMO (LPL) trilayer epitaxial films were systemically studied. The superlattice structures of multilayer films were observed according to the diffraction peaks of X-ray diffraction patterns at small angles. The metal–insulator transition temperature (T_P) and peak resistivity (ρ_max) obviously changed when we altered the thickness of PCMO middle layer and the intra-field related with the thickness of those layers and their interaction. Considering the effect of the distribution of electrical field and current, and the interaction among the layers of LSMO and PCMO, an effective fact n* was introduced to replace n (the number of layer). All the calculated values of ρ (the resistivity of multilayer films) accorded with the experimental values.     

Comparative study of electrical properties of Au/n-Si (MS) and Au/Si3N4/n-Si (MIS) Schottky diodes

In this paper, the electrical parameters of Au/n-Si (MS) and Au/Si₃N₄/n-Si (MIS) Schottky diodes are obtained from the forward bias current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature. Experimental results show that the rectifying ratios of MS and MIS diode at ± 5 V are found to be 1.25×10³ and 1.27×10⁴, respectively. The main electrical parameters of MS and MIS diode, such as the zero-bias barrier height (Φ _Bo) and ideality factor (n) are calculated to be 0.51 eV (I-V), 0.53 eV (C-V), and 4.43, and 0.65 eV (I-V), 0.70 eV (C-V), and 3.44, respectively. Also, the energy density distribution profile of the interface states (N_ss) is obtained from the forward bias I-V. In addition, the values of series resistance (R_s) for the two diodes are calculated from Cheung's method and Ohm's law.     

Investigation of inhomogeneous barrier height of Au/Bi4Ti3O12/n-Si structure through Gaussian distribution of barrier height

Au/Bi₄Ti₃O₁₂/n-Si structure is fabricated in order to investigate its current-voltage (I-V) characteristics in a temperature range of 300 K-400 K. Obtained I-V data are evaluated by thermionic emission (TE) theory. Zero-bias barrier height (Φ_B0) and ideality factor (n) calculated from I-V characteristics, are found to be temperature-dependent such that Φ_B0 increases with temperature increasing, whereas n decreases. Obtained temperature dependence of Φ_B0 and linearity in Φ_B0 versus n plot, together with lower barrier height and Richardson constant values obtained from Richardson plot, indicate that the barrier height of the structure is inhomogeneous in nature. Therefore, I-V characteristics are explained on the basis of Gaussian distribution of barrier height.     

Characterization of vertical Au/β-Ga_2O_3 single-crystal Schottky photodiodes with MBE-grown high-resistivity epitaxial layer

High-resistivity β-Ga_2O_3 thin films were grown on Si-doped n-type conductive β-Ga_2O_3 single crystals by molecular beam epitaxy(MBE).Vertical-type Schottky diodes were fabricated,and the electrical properties of the Schottky diodes were studied in this letter.The ideality factor and the series resistance of the Schottky diodes were estimated to be about1.4 and 4.6×10~6 Ω.The ionized donor concentration and the spreading voltage in the Schottky diodes region are about4×10~(18)cm~(-3) and 7.6 V,respectively.The ultra-violet(UV) photo-sensitivity of the Schottky diodes was demonstrated by a low-pressure mercury lamp illumination.A photoresponsivity of 1.8 A/W and an external quantum efficiency of8.7 ×10~2%were observed at forward bias voltage of 3.8 V,the proper driving voltage of read-out integrated circuit for UV camera.The gain of the Schottky diode was attributed to the existence of a potential barrier in the i-n junction between the MBE-grown highly resistive β-Ga_2O_3 thin films and the n-type conductive β-Ga_2O_3 single-crystal substrate.     

On the barrier inhomogeneities of polyaniline/p-Si/Al structure at low temperature

The current–voltage (I–V) characteristics of Au/polyaniline(PANI)/p-Si/Al structures were determined at various temperatures in the range of 90–300 K. The evaluation of the experimental I–V data reveals a decrease of the zero-bias barrier height (BH) and an increase of the ideality factor (n) with decreasing temperature. It was shown that the occurrence of a Gaussian distribution of then BHs is responsible for the decrease of the apparent BH, increase of the ideality factor n due to barrier height imhomogeneities that prevail at the interface. A Φ_b0 versus 1/T plot has been drawn for evidence of the Gaussian distribution of the barrier height, and and σ₀ = 0.0943 V for the mean barrier height and zero-bias standard deviation, respectively, have been obtained from this plot. Thus, a modified versus 1/T plot gives and A^* as 0.885 eV and A^* = 55.80 A/K² cm², respectively. Hence, it can be concluded that Au/PANI/p-Si/Al structure has a good rectifying contact and the temperature dependence of I–V characteristics of the rectifying contact on p-Si successfully have been explained on the basis of TE mechanism with Gaussian distribution of the barrier heights.     

Thermoelectric power and irreversibility field of (Hg,Tl)2Ba2Can−1CunOy (n=2–5) superconductors

We have measured the thermoelectric power, S, and the irreversibility field, H_irr, of the superconducting samples of (Hg,Tl)₂Ba₂Ca_n−1Cu_nO_y (n=2–5). S values for the (Hg,Tl)-22(n−1)n above their T_c's drastically increase with increasing n. Judging from the S values at room temperature, the n=2 and 3 samples are located in the overdoped region, the n=4 is in the almost optimally doped and the n=5 is in the underdoped region. H_irr values for the n=4 and 5 samples are higher than those for the as-synthesized and annealed n=3 samples. It is considered that the enhancement in H_irr is due not only to the increase of hole concentration but to the increase in the number of CuO₂ sheets.     

Accurate measurement of the refractive index of CO2, N2, He, O2, and air at 10.57 μ and T = 23 °C

The refractive index of carbon-dioxide, nitrogen, helium, oxygen and air have been measured at 23 °C temperature by means of a tunable CO₂ laser at 10.57 μm and of a differential interferometric technique. As the gas refractive index depends on the pressure P as n = 1 + _PP, the pressure coefficients _P has been measured with 5e–3 accuracy.     

Direct measurement of the magnetocaloric effect in La0.67Ca0.33MnO3

Polycrystalline perovskite La_0.67Ca_0.33MnO₃ was synthesized by a sol–gel method. Its adiabatic temperature change ΔT_ad induced by a magnetic field change was measured directly. At 268 K, near its Curie temperature T_C, ΔT_ad of La_0.67Ca_0.33MnO₃ induced by a magnetic field change of 2.02 T reaches 2.4 K. The latent heat Q and magnetic entropy change −ΔS_M induced by a magnetic field change were calculated from the temperature dependence of ΔT_ad and zero-field heat capacity C_p. The maximum values of Q and −ΔS_M in La_0.67Ca_0.33MnO₃ induced by a magnetic field change of 2.02 T are 1.85 J g⁻¹ and 6.9 J kg⁻¹ K⁻¹, respectively. The former is larger than the phase transition latent heat of heating or cooling, which is about 1.70 J g⁻¹.     

Kinetics study of a-Se80Te20−xPbx using non-isothermal crystallization

The kinetics of crystallization in Se₈₀Te_20−xPb_x (x=0, 2, 6 and 10) glasses is studied by non-isothermal method using differential scanning calorimetry (DSC). DSC is performed at different heating rates of 5, 10, 15 and 20 K/min. The values of glass transition and crystallization temperatures are found to be composition and heating-rate dependent. From the heating-rate dependence of the glass transition and crystallization temperatures, the activation energy of crystallization (ΔE_c) and order parameter (n) are calculated.     

Fabrication of high quality silicon–polyaniline heterojunctions

A high quality silicon–polyaniline heterojunction is produced by spin-coating of soluble polyaniline on silicon substrates. The devices have excellent reproducibility of their electrical characteristics and high rectification ratio. The rectification ratio is 60,000 at ±1.0 V at room temperature, and typical reverse current at −1.0 V is 3 nA. A G/I×G plot is used to analyze the current–voltage characteristics, yielding typical series resistance of 4 kΩ and ideality factor in a range from 1.0 to 2.0. The devices present great potential for use as radiation and/or gas sensors.     

Composition and thermal-induced effects on the optical constants of Ge20Se80−xBix thin films

 The effects of composition and thermal annealing near crystallization temperature, T_c on the optical and structural properties of Ge₂₀Se_80−xBi_x (x=0, 2.5, 5 and 7.5 at%) was investigated. The influence of incorporation Bi content in Ge₂₀Se_80−xBi_x system results in a gradual decrease in the indirect optical gap from 1.89 to 1.44 eV, this behavior can be explained as increased tailing. On annealing, the optical band gap E_g decreases gradually for the crystallized films while the refractive index increases, this behavior can be attributed to transformation from amorphous to crystalline and was explained in the light of dangling bond model. The refractive index n of as-prepared and annealed films has been analyzed according to the Wwmple–DiDominico single oscillator model and the values of E_o and E_d were determined. The effect of annealing on the nature and degree of crystallization has been investigated by studying the structure using transmission electron microscope, X-ray diffraction and scanning electron microscope.     

The effects of the ageing on the characteristic parameters of polyaniline/p-type Si/Al structure

A detailed study of the effects of the ageing on the characteristic parameters of polyaniline/p-type Si/Al structure has been presented. The polyaniline film has been formed on a p-type Si substrate by means of an anodization process. The polyaniline/p-Si/Al structure has demonstrated clearly rectifying behavior by the current–voltage (I–V) curves studied at room temperature. The current–voltage curves of the structure have been measured immediately, 15, 30, 60, 90 and 120 days after fabrication of the polyaniline/p-Si/Al structure. It has been seen that the characteristic parameters, such as barrier height (BH), ideality factor and series resistance of polyaniline/p-type Si/Al structure have slowly changed with increasing ageing time. The diode shows non-ideal I–V behavior with an ideality factor greater than unity that can be ascribed to the interfacial layer, the interface states and the series resistance.     

Structural and electrical properties of crystalline (1−x)Ta2O5−xTiO2 thin films fabricated by metalorganic decomposition

Polycrystalline (1−x)Ta₂O₅−xTiO₂ thin films were formed on Si by metalorganic decomposition (MOD) and annealed at various temperatures. As-deposited films were in the amorphous state and were completely transformed to crystalline after annealing above 600 °C. During crystallization, a thin interfacial SiO₂ layer was formed at the (1−x)Ta₂O₅−xTiO₂/Si interface. Thin films with 0.92Ta₂O₅–0.08TiO₂ composition exhibited superior insulating properties. The measured dielectric constant and dissipation factor at 1 MHz were 9 and 0.015, respectively, for films annealed at 900 °C. The interface trap density was 2.5×10¹¹ cm⁻² eV⁻¹, and flatband voltage was −0.38 V. A charge storage density of 22.8 fC/μm² was obtained at an applied electric field of 3 MV/cm. The leakage current density was lower than 4×10⁻⁹ A/cm² up to an applied electric field of 6 MV/cm.