Effect of series resistance on the performance of silicon Schottky diode in the presence of tin oxide layer

The current–voltage (I–V) characteristics of Al/SnO₂/p-Si (MIS) Schottky diodes prepared by means of spray deposition method have been measured at 80, 295 and 350 K. In order to interpret the experimentally observed non-ideal Al/SnO₂/p-Si Schottky diode parameters such as, the series resistance R_s, barrier height Φ_B and ideality factor n, a novel calculation method has been reported by taking into account the applied voltage drop across interfacial oxide layer V_i and ideality factor n in the current transport mechanism. The values obtained for V_i were subtracted from the applied voltage values V and then the values of R_s were recalculated. The parameters obtained by accounting for the voltage drop V_i have been compared with those obtained without considering the above voltage drop. It is shown that the values of R_s estimated from Cheung’s method were strongly temperature-dependent and decreased with increasing temperature. It is shown that the voltage drop across the interfacial layer will increase the ideality factor and the voltage dependence of the I–V characteristics. The interface state density N_ss of the diodes has an exponential growth with bias towards the top of the valance band for each temperature; for example, from 2.37 × 10¹³ eV⁻¹ cm⁻² in 0.70−E_v eV to 7.47 × 10¹³ eV⁻¹ cm⁻² in 0.62−E_v eV for 295 K. The mean N_ss estimated from the I–V measurements decreased with increasing the temperature from 8.29 × 10¹³ to 2.20 × 10¹³ eV⁻¹ cm⁻².     

Analysis of current–voltage and capacitance–voltage characteristics of perylene-monoimide/n-Si Schottky contacts

The electrical and interface state properties of Au/perylene-monoimide (PMI)/n-Si Schottky barrier diode have been investigated by current–voltage (I–V) and capacitance–voltage (C–V) measurements at room temperature. A good rectifying behavior was seen from the I–V characteristics. The series resistance (R_s) values were determined from I–V and C–V characteristics and were found to be 160 Ω and 53 Ω, respectively. The barrier height (Φ_b) of Au/PMI/n-Si Schottky diode was found to be 0.694 eV (I–V) and 0.826 eV (C–V). The ideality factor (n) was obtained to be 4.27 from the forward bias I–V characteristics. The energy distribution of interface state density (N_ss) of the PMI-based structure was determined, and the energy values of N_ss were found in the range from E_c ? 0.508 eV to E_c ? 0.569 eV with the exponential growth from midgap toward the bottom of the conduction band. The values of the N_ss without R_s are 2.11 × 10¹² eV^?1 cm^?2 at E_c ? 0.508 eV and 2.00 × 10¹² eV^?1 cm^?2 at E_c ? 0.569 eV. Based on the above results, it is clear that modification of the interfacial potential barrier for metal/n-Si structures has been achieved using a thin interlayer of the perylene-monomide.     

The role of hybridization on valence transitions in the spinless Falicov-Kimball model

The spinless Falicov-Kimball model with hybridization is studied in one dimension using small-cluster exact-diagonalization calculations. The resultant exact solutions are used to examine the f-state occupation n ^f as a function of f-level energy E _f, hybridization V and d-f interaction U. In addition, the phase diagram based on the finite-size scaling analysis of the single particle excitation energy is discussed both for the symmetric (E _f = 0) and unsymmetric (E _f ≠ 0) case. A number of remarkable results are found. (i) The f-electron occupation number as a function of E _f changes continuously, confirming renormalization-group results. No discontinuous transitions are observed at finite V. (ii) In the symmetric case the insulating state persists as the ground state for all nonzero V. (iii) Outside the symmetric point the hybridization stabilizes the metallic state for lower V and the insulating state for higher V. (iv) The metal-insulator transition takes place at V = V _c > 0. The values of the critical hybridization strength V _c are of order 10^?2.     

Luminescence response of CsI:Na to electron pulse irradiation

This paper investigates the influence of activator concentration and temperature on the scintillation process in CsI:Na crystal which was excited by a pulsed electron beam (E_ex = 0.25 MeV, t_1/2 = 15 ns, W = 0.003…0.16 J/cm²) at temperature within 77–300 K. It has been established that the transition of Na-bound two halide exciton from singlet state causes 3 eV emission of CsI:Na. The capturing of V_k by Na⁺ ion determines the scintillation pulse shape. Thermal liberation of V_k from V_kA centers results in an inertial rise of the emission pulse in lightly activated CsI:Na and in a mono-exponential decay of the emission pulse in heavily activated CsI:Na. The value of thermal dissociation energy of V_kA centers is 0.24 ± 0.01 eV, which was obtained from the temperature dependences of the emission decay time constant for CsI:2.8∙10⁻³%Na and of the rise time constant for CsI:2.0∙10⁻⁴%Na.     

A thermal and electrochemical properties research on gel polymer electrolyte membrane of lithium ion battery

N-methyl-N-propyl-piperidin-bis(trifluoromethylsulfonyl)imide/bis(trifluoromethylsulfonyl) imide lithium base/polymethyl methacrylate(PP₁₃TFSI/LiTFSI/PMMA) gel polymer electrolyte (GPE) membrane was prepared by in situ polymerization. The physical and chemical properties were comprehensively discussed. The decomposition characteristics were emphasized by thermogravimetric (TG-DTG) method in the nitrogen atmosphere at the different heating rates of 5, 10, 15 and 20 °C min⁻¹, respectively. The activation energy was calculated with the iso-conversional methods of Ozawa and Kissinger, Friedman, respectively, and the Coats-Redfern methods were adopted to employ the detailed mechanism of the electrolyte membrane. The equation f(α)=3/2[(1−α)^1/3−1] was quite an appropriate kinetic mechanisms to describe the thermal decomposition process with an activation energy (E_α) of 184 kJ/mol and a pre-exponential factor (A) of 1.894×10¹¹ were obtained.     

A study of electrical enhancement of polycrystalline MgZnO/ZnO bi-layer thin film transistors dependence on the thickness of ZnO layer

A polycrystalline MgZnO/ZnO bi-layer was deposited by using a RF co-magnetron sputtering method and the MgZnO/ZnO bi-layer TFTs were fabricated on the thermally oxidized silicon substrate. The performances with varying the thickness of ZnO layer were investigated. In this result, the MgZnO/ZnO bi-layer TFTs which the content of Mg is about 2.5 at % have shown the enhancement characteristics of high mobility (6.77–7.56 cm² V⁻¹ s⁻¹) and low sub-threshold swing (0.57–0.69 V decade⁻¹) compare of the ZnO single layer TFT (μ_FE = 5.38 cm² V⁻¹ s⁻¹; S.S. = 0.86 V decade⁻¹). Moreover, in the results of the positive bias stress, the ΔV_on shift (4.8 V) of MgZnO/ZnO bi-layer is the 2 V lower than ZnO single layer TFT (ΔV_on = 6.1 V). It reveals that the stability of the MgZnO/ZnO bi-layer TFT enhanced compared to that of the ZnO single layer TFT.     

Study of the reaction238U (α, α′f) atE α=480 MeV

The excitation function of the fission probability P _E E _x) for²³⁸U has been measured in the reaction²³⁸U(α, α′ f) at 480 MeV bombarding energy. The reaction mechanism of this reaction is discussed for excitation energies belowB _nf , the threshold for second chance fission, and aboveB _nf up toE _x =37 MeV. In comparing with results from fission induced by photons and by particle transfer reactions the (α, α′f) reaction gives too low values for the fission probabilityP _f at excitation energies well aboveB _nE . The role of the quasi-elastic knock-out process in this reaction is discussed.     

Microstructures and microwave dielectric properties of La1-xBx(Mg0.5Sn0.5)O3 ceramics

The microwave dielectric properties of La_1-xB_x(Mg_0.5Sn_0.5)O₃ ceramics were examined with a view to their exploitation for mobile communication. The La_1-xB_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La_0.995B_0.005(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A maximum apparent density of 6.58 g/cm³, a dielectric constant (ε_r) of 19.8, a quality factor (Q × f) of 41,800 GHz, and a temperature coefficient of resonant frequency (τ_f) of −86 ppm/°C were obtained for La_0.995B_0.005(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1500 °C for 4 h.     

Raman scattering study of IrxRu1−xO2 mixed metal oxide nanowires (0 ≤ x ≤ 1)

Recent interests in mixed metal oxide nanostructured materials especially Ir_xRu_1−xO₂ compounds have been mainly driven by the technological application as electrocatalyst and electrode materials. We present room temperature Raman scattering results of single crystalline Ir_xRu_1−xO₂ (0 ≤ x ≤ 1) nanowires grown by atmospheric pressure chemical vapor deposition. We observed that the E_g, the A_1g, and the B_2g phonon modes of a single Ir_xRu_1−xO₂ nanowire are blue-shifted linearly with respect to the Ir contents from which we could get stoichiometry information. We also observed that the asymmetric lineshape and the broadening of the full width at half maximum of the E_g mode that involves the out-of-plane oxygen vibration. The unusual asymmetric broadening of the E_g phonon can be explained by the activation of the non-zone-center phonons due to substitutional disorder present in the system. We also found that there is a mixed mode of the A_1g and the B_2g phonons due to the substitutional disorder, in the range of 630–750 cm⁻¹.     

The effect of series resistance and interface states on the frequency dependent C–V and G/w–V characteristics of Al/perylene/p-Si MPS type Schottky barrier diodes

The capacitance–voltage–frequency (C–V–f) and conductance–voltage–frequency (G/w–V–f) characteristics of Al/perylene/p-Si Schottky barrier diodes (SBDs) fabricated with spin coating system have been investigated in the frequency range of 30 kHz–2 MHz at room temperature. In order to elucidate the electrical characteristics of SBDs with perylene interface, the voltage and frequency dependent series resistance (R_s), frequency dependent density distribution profile of interface state (N_ss) were obtained. The measurements of C and G/w were found to be strongly dependent on bias voltage and frequency for Al/perylene/p-Si SBDs. For each frequency, the R_s–V plot gives a peak, decreasing with increasing frequencies. Also, it has been shown that the interface states density exponentially decreases with increasing frequency. The C–V–f and G/w–V–f characteristics confirm that the N_ss and R_s of the diode are important parameters that strongly influence the electric parameters in metal/polymer/semiconductor (MPS) structure.     

Optically stimulated luminescence (OSL) and thermally assisted OSL in Eu2+ – Doped BaSO4 phosphor

BaSO₄:Eu²⁺ phosphor has been investigated for its photoluminescence (PL), thermoluminescence (TL), TL kinetics, optically stimulated luminescence (OSL) and thermally assisted OSL (TA-OSL) response. PL spectra showed the characteristic emission of Eu²⁺ ion at 375 nm when excited by 320 nm. The luminescence lifetime has been measured as 40 and 628 μs of fast and slow components respectively. The TL parameters such as trap depth (E), frequency factor (s) and the order of kinetics (b) are determined. The phosphor is found to be 6 and 4 times more sensitive than CaSO₄:Dy and α-Al₂O₃:C, respectively, in TL mode. However, its OSL sensitivity is 75% of α-Al₂O₃:C. It is found to possess three OSL components having photoionization cross-sections of 1.4 × 10⁻¹⁷, 1.2 × 10⁻¹⁸ and 5.2 × 10⁻¹⁹ cm² respectively. The temperature dependence of OSL studies showed that integrated TA-OSL signal increases with stimulation temperature between 50 and 250 °C, while between 260 and 450 °C the signal intensity decreases. This behavior is interpreted to arise from competing effects of thermal assistance (activation energy E_A = 0.063 ± 0.0012 eV) and depletion of trapped charges. This increase of OSL at elevated temperature can be employed for enhancing the sensitivity of phosphor for radiation dosimetry.     

Low energy photoelectron spectroscopy of solids. Aspects of experimental methodology concerning metals and insulators

Both He(I) and He(II) ultraviolet photoelectron spectra (UPS) for metals (Ag, Au) and thin solid films of organic (anthracene) and inorganic compounds (LiF, LiCl, LiBr, LiI, NaF, NACl, Li₂SO₄, NaOH) are presented. The results of measurements on two different spectrometers have shown that both the bias voltage, V_b, applied to the solid sample, and the angle of incidence, Ø, of the photon beam with the sample are crucial to the accurate determination of the work function (metals) and binding energies (insulators). The true binding energy of a band in the UPS with respect to the vacuum level, E_b^vac, is defined as the minimum value of (hv - ΔE), where ΔE is the energy difference between the threshold of the SEED, E_T, and the band maximum. ΔE is maximized at low values of ø and of V_b. The intensity of photoelectron emission (signal) increases with both ø (2–30°) and V_b (5–20 V). It is recommended that the variation of ΔE with both ø and V_b should be observed in any determination of E_B^vac.     

Influence of a magnetic field on the electronic Raman response in high-Tc cuprates

The effect of a magnetic field parallel to the CuO₂ plane on the Raman spectra is investigated based on the Slave–Boson approach to the t − t′ − J model with a Zeeman field and the random-phase approximation. We find that the Raman spectra intensities in the superconducting (SC) state are suppressed for both the B_1g and the B_2g channels with a slight shift of the peaks position toward lower frequency in the B_1g channel and a negligible shift in the B_2g channel due to the Zeeman splitting. There is a field-induced peak and dip structure at low energy response in the B_2g channel at very low temperature. While rising temperature has a similar effect in reducing the Raman response peak in the superconducting (SC) state, it smears out the field-induced peak and dip structure in the B_2g channel. We compare these results with experiments and give explanations based on the field-induced changes of the density of the superconducting condensate, the momentum distribution of the quasiparticle energy and the scattering rate.     

2,7-Carbazole and thieno[3,4-c]pyrrole-4,6-dione based copolymers with deep highest occupied molecular orbital for photovoltaic cells

Three kinds of donor–acceptor (D–A) type photovoltaic polymers were synthesized based on 2,7-carbazole and thieno[3,4-c]pyrrole-4,6-dione (TPD). The conjugation of weakly electron (e)-donating 2,7-carbazole and strongly e-accepting TPD moieties yielded a deep highest occupied molecular orbital (HOMO) and its energy level was fine-controlled to be −5.72, −5.67 and −5.57 eV through the incorporation of thiophene (T), thieno[3,2-b]thiophene (TT) and bithiophene (BT) as a π-bridge. Polymer:[6,6]-phenyl-C₇₁ butyric acid methyl ester (PC₇₁BM) based bulk heterojunction solar cells exhibited a high open-circuit voltage (V_OC) in the range, 0.86–0.94 V, suggesting good agreement with the measured HOMO levels. Despite the high V_OC, the thiophene (or thienothiophene)-containing PCTTPD (or PCTTTPD) showed poor power conversion efficiency (PCE, 1.14 and 1.25%) because of the very low short-circuit current density (J_SC). The voltage-dependent photocurrent and photoluminescence quenching measurements suggested that hole transfer from PC₇₁BM to polymer depends strongly on the HOMO level of the polymer. The PCTTPD and PCTTTPD devices suffered from electron–hole recombination at the polymer/PC₇₁BM interfaces because of the insufficient energy offset between the HOMOs of the polymer and PC₇₁BM. The PCBTTPD:PC₇₁BM device showed the best PCE of 3.42% with a V_OC and J_SC of 0.86 V and 7.79 mA cm⁻², respectively. These results show that photovoltaic polymers should be designed carefully to have a deep HOMO level for a high V_OC and sufficient energy offset for ensuring efficient hole transfer from PC₇₁BM to the polymer.     

Effective Mode Volume of Nanoscale Plasmon Cavities

The controlled squeezing of electromagnetic energy into nanometric volumes via surface plasmon-polariton excitations in plasmonic nanoresonators is analyzed using the concept of an effective electromagnetic mode volume V _eff, while taking careful account of the plasmon-polariton dispersion and the electromagnetic energy stored in the metal. Together with the quality factor Q of the cavity resonance, this enables a comparison with dielectric optical cavities, where V _eff is limited by diffraction. For a Fabry–Perot type planar metallic cavity, a one-dimensional analytic model as well as a three-dimensional finite-difference time-domain simulation reveal that V _eff is not bounded by diffraction, and that Q/V _eff increases for decreasing cavity size. In this picture, matter–plasmon interactions can be quantified in terms of Q and V _eff, and a resonant cavity model for the enhancement of spontaneous Raman scattering is presented.     

Exact saturation and degeneracy of isospin bounds and zeros trajectories in pion-nucleon scattering: D. B. Ion. Joint Institute for Nuclear Research,Dubna, Moscow,P. O. Box 79, U.S.S.R.

By exploiting the analogy between the classical equation of heat conduction and the Bloch equation, the canonical density matrix is calculated exactly for noninteracting electrons in a finite step model of a metal surface. This result is then used to calculate the spatial variation of the electron density ?(z) as a function of distance z from the planar metal surface. In particular an expansion in inverse powers of $\text{V}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and V, V being the step height, is derived. The low-order terms are used to compute the electron density at the surface of Al metal: There is good agreement with a full numerical evaluation. Finally, in the limit $\text{V}\text{E}{}_{\mathrm{f}}\text{→ ∞}$, E_f being the Fermi energy, the change in the shape and size of the exchange (Fermi) hole surrounding an electron is studied as the electron moves into the vicinity of a metal surface. The anisotropy of the Fermi hole is large and the implications for one-body potential theory are briefly discussed.     

Field dependence of a.c. Electroluminescence in ZnS: Mn,Cu, Cl film panels

Electroluminescent (EL) film panels of ZnS: Mn, Cu, Cl operated by a.c. electric field are studied at room temperature. The emission spectrum consists of a single peak at 590 nm. The EL emittance B varies with frequency f of the applied a.c. electric field as B = B_s ? B_m exp ? f/f_c where B_s, B_m and f_c are constants. This equation indicates that B approaches a saturation value B_s when f?f_c and a linear relation between B and f when f?f_c. At a fixed frequency f, B is found to depend on the applied voltage V as B = A exp [-G/F + V^{$\text{1}\text{2}$})] where A, G and F are constants. This formula is valid at all stages of the operating life of the film panel.     

Energy resolved imaging with a stratified phosphor detector

Polycrystalline solid state solutions of Ba_ySr_1 − yCl₂ have been produced; these adopt the cubic fluorite phase for y ≤ 0.30. The cubic structure minimizes optical scattering from grain boundaries, and so for y ≤ 0.30 the materials are transparent, a key advantage for ceramic scintillators and phosphors. The substitution of Sr²⁺ ions with Ba²⁺ ions has the advantage that it substantially increases the x-ray absorption coefficient with respect to pure SrCl₂. Additional doping with rare earth ions such as Sm²⁺ and Eu²⁺ gives bright x-ray phosphor materials. The Sm or Eu-doped materials show a broad 4f⁵5 d¹ → 4f⁶ emission peaked at 685 nm or a broad 4f⁶5 d¹ → 4f⁷ emission peaked at 406 nm respectively. These materials have been tested as x-ray phosphors and the spatial resolution was determined to be at least 6 LP/mm, whilst the x-ray radioluminescence intensity is around 40% that of the commercial x-ray phosphor Gd₂O₂S:Tb. A stratified phoswich structure, comprising Eu and Sm-doped layers of Ba_ySr_1 − yCl₂ was produced in which the relative intensities of the two emissions varies with x-ray beam energy; this can be used for energy discrimination in imaging by way of emission spectra as opposed to the more commonly used pulse shape discrimination. A dual energy imaging technique based on these bi-layered structures and utilizing a semi-professional grade digital SLR camera is described and composition-sensitive imaging has been demonstrated.     

New method to calibrate binding energy using Au nanocolloids in X-ray photoelectron analysis of diamondlike carbon films with different electrical resistivities

A new method to calibrate the binding energy (E_B) using Au nanocolloids as a calibrant in XPS analysis of diamondlike carbon (DLC) is proposed by considering the DLC films with different electrical resistivities. A few microliters of a dilute aqueous solution containing Au nanocolloids were dropped onto a small local surface area of the DLC film, which became a stain before XPS measurements by gradually drying in vacuo. The observed peak E_B of the C 1s spectrum at another native surface (an area without Au nanocolloids) of the DLC film was calibrated by setting that of the Au 4f_7/2 spectrum of the Au nanocolloids to 84.0 (83.98 ± 0.02) eV. The adequacy of this method was investigated by considering the correlation among the full width at half maximums (FWHMs) of the Au 4f_7/2 spectra of the Au nanocolloids on the DLC surfaces and that of a Au plate as a reference. Consequently, the FWHM of the Au 4f_7/2 spectrum of the Au nanocolloids on the DLC surface is a candidate to investigate the differential charging effect of the DLC surface, and the calibration method is reliable if the FWHM agrees with that of the Au plate.     

Electronic structure and energies of interatomic bonds in the TiSi<Subscript>2</Subscript> compound with a <Emphasis Type="Italic">C</Emphasis>49 crystal structure

Full-electron calculations of the electronic structure of the TiSi₂ compound in the structural modification C49 are performed using the augmented-plane-wave method. The total energy, the electronic band structure, and the density of states are calculated for an extended translational unit cell Ti₄Si₈, which is formed during the growth of a silicon nanowire on a p-Si substrate. Calculations are also carried out for two orthorhombic unit cells of the nonstoichiometric compositions Ti₃Si₉ and Ti₅Si₇. The energies of the interatomic bonds are determined to be E _Si-Si = 1.8 eV, E _Ti-Ti = 2.29 eV, and E _Ti-Si = 4.47 eV. The dependence of the total energy of the unit cell E _tot(V) on the unit cell volume V is obtained by optimizing the unit cell volume. The bulk modulus B ₀ = 132 GPa is determined from the Murnaghan equation of state for solids and the dependence E _tot (V). This value of the bulk modulus is used to estimate the activation energy for interstitial diffusion of silicon atoms Q _i(Si) ≈ 0.8 eV.