M. Sağlam

Interpreting the nonideal reverse bias C-V characteristics and importance of the dependence of Schottky barrier height on applied voltage

This work presents an attempt related to the charging behaviour of interface states to the nonideal forward bias current-voltage (I-V) and the reverse bias capacitance-voltage (C-V) characteristics of AlnSi Schottky barrier diodes. The diode showed nonideal I-V behaviour with an ideality factor of 1.50 and was thought to have a metal-interface layer-semiconductor configuration. Considering that the interface states localized at the interfacial layer-semiconductor interface are in equilibrium with the semiconductor, the energy distribution of the interface states was exactly determined from the forward bias I-V characteristics by taking into account the bias dependence of the effective barrier height, θe. The determination of the intercept voltage and interface state density was made by means of a simple interface charge model which has been developed in detail. The I-V characteristics were used for determining the voltage dependence of the barrier height. Although the change in barrier height with applied biasis small, it is important for exactly determining the shape of the interface state density distribution curve. At a frequency of 500 kHz, the nonlinear reverse bias C−2−V plot with the curvature concave downward has been only thought of to be due to the contribution of the capacitance of the interface state charges. It is concluded that the nonlinear nature of C−2−V plots in the frequency range 50–200 kHz has been caused by the interface state charges as well as inversion layer and inversion layer charges. It has been understood by means of the interface state charge model that the C−2−V plots cannot only be interpreted in terms of the contribution of the interface state charges to the device capacitance.

The bias-dependence change of barrier height of Schottky diodes under forward bias by including the series resistance effect

Schottky barrier height shifts depending on the interfacial layer as well as a change of the interface state charge with the forward bias while considering the presence of bulk (semiconductor) series resistance are discussed both theoretically and experimentally. It has been concluded that the barrier height shift or increase in Schottky diodes is mainly due to the potential change across the interfacial layer and the occupation of the interface states as a result of the applied forward voltage. One assumes that the barrier height is controlled by the density distribution of the interface states in equilibrium with the semiconductor and the applied voltage. In nonideal Schottky diodes, the values of the voltage drops across the interfacial layer, the depletion layer and the bulk resistance are given in terms of the bias dependent ideality factor, n, different from those in literature. These values are determined by a formula obtained for Vi and Vs by means of change of the interface charge with bias.

Effect of series resistance on the forward current-voltage characteristics of Schottky diodes in the presence of interfacial layer

Abstract In order to make an accurate determination of Schottky diode parameters such as the ideality factor, the barrier height and the series resistance [using forward current-voltage ( I - V ) characteristics in the presence of an interfacial layer], a novel calculation method has been developed by taking into account the applied voltage drop across the interfacial layer ( V i ). The parameters obtained by accounting for the voltage drop V i have been compared with those obtained without considering the above voltage drop. To examine the consistency of this approach, the comparison has been made by means of Schottky diodes fabricated on a n -type semiconductor substrate with different bulk thickness. 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. In addition, it is shown that the series resistance value increases as the semiconductor bulk thickness has been increased.

Antiulcer activity of fluvoxamine in rats and its effect on oxidant and antioxidant parameters in stomach tissue

BackgroundAlthough many drugs are available for the treatment of gastric ulcers, often these drugs are ineffective. Many antidepressant drugs have been shown to have antiulcer activity in various models of experimental ulcer. One such drug, the antidepressant mirtazapine, has been reported to have an antiulcer effect that involves an increase in antioxidant, and a decrease in oxidant, parameters. To date, however, there is no information available regarding the antiulcer activity for a similar antidepressant, fluvoxamine. This study aimed to investigate the antiulcer effects of fluvoxamine and to determine its relationship with antioxidants.MethodsGroups of rats fasted for 24 h received fluvoxamine (25, 50, 100 and 200 mg/kg), ranitidine (50 mg/kg) or distilled water by oral gavage. Indomethacin (25 mg/kg) was orally administered to the rats as an ulcerative agent. Six hours after ulcer induction, the stomachs of the rats were excised and an ulcer index determined. Separate groups of rats were treated with the same doses of fluvoxamine and ranitidine, but not with indomethacin, to test effects of these drugs alone on biochemical parameters. The stomachs were evaluated biochemically to determine oxidant and antioxidant parameters. We used one-way ANOVA and least significant difference (LSD) options for data analysis.ResultsThe 25, 50, 100 and 200 mg/kg doses of fluvoxamine exerted antiulcer effects of 48.5, 67.5, 82.1 and 96.1%, respectively, compared to the control rat group. Ranitidine showed an 86.5% antiulcer effect. No differences were observed in the absence of indomethacin treatment for any dose of fluvoxamine or for ranitidine. The levels of antioxidant parameters, total glutathione and nitric oxide, were increased in all fluvoxamine groups and in the ranitidine group when compared with the indomethacin-only group. In addition, fluvoxamine and ranitidine decreased the levels of the oxidant parameters, myeloperoxidase and malondialdeyhyde, in the stomach tissues of the rats when compared to indomethacin group.ConclusionWe conclude that fluvoxamine has antiulcer effects, and that these occur by a mechanism that involves activation of antioxidant parameters and inhibition of some toxic oxidant parameters.

Determination of the lateral barrier height of inhomogeneous Au/n-type InP/In schottky barrier diodes

We have identically prepared Au/n-InP/In Schottky barrier diodes (SBDs). The barrier height for the Au/n-InP/In SBDs from the current–voltage characteristics has varied from 0.557 eV to 0.615 eV, and the ideality factor n from 1.002 to 1.087. We have determined a lateral homogeneous barrier height value of approximately 0.597 eV for the Au/n-InP/In SBD from the experimental linear relationship between barrier heights and ideality factors. The barrier height value obtained from the reverse bias C−2–V characteristics has varied from 0.512 eV to 0.572 eV and statistical analysis yields the mean Φ(C–V) = 0.562 ± 0.004 eV. A doping density of about (2.90 ± 0.05) × 1015 cm−3 has been determined from the reverse bias C−2–V characteristics.

Effect of thermal annealing in nitrogen on the I-V and C-V characteristics of Cr-Ni-Co alloy/LEC n-GaAs Schottky diodes

The Schottky barrier height and ideality factor n of Cr - Ni - Co alloy Schottky contacts on an n-LEC GaAs substrate have been measured using current - voltage (I - V) and capacitance - voltage (C - V) techniques after different thermal annealings for 5 min in (temperature range from 300 to ). The values of and n for the forward I - V characteristics range from 0.65 and 1.001 eV at room temperature (RT) to 0.86 and 1.095 eV at . Thereby, the barrier height enhancement has been explained in terms of the presence of microclusters of one or more interface phases produced by reactions between the alloy and GaAs or the native oxide layer. The stability value of 1.010 for n from the RT to annealing has been ascribed to reduction of the native oxide layer on the GaAs surface by Cr in the alloy. The C - V relationship of the Cr - Ni - Co/n-GaAs Schottky diode at 1 MHz gives values of 0.68, 0.74 and 0.85 eV for at RT, and annealing temperatures respectively. The fact that the - V curves after annealing above show two linear regions separated by a transition segment has been attributed to the diffusion of Cr into GaAs during the thermal annealing process.

Current-voltage and capacitance-voltage characteristics of metallic polymer/InSe(:Er) Schottky contacts

Abstract An investigation of metallic polypyrrole polymer (MPP)/ n -InSe(:Er) (by an anodization process) Schottky barrier diodes (SBDs) fabricated on a cleaved n -type InSe(:Er) substrate, which is a layered semiconductor, has been made. The metallic polypyrrole film provides a good rectifying contact to the n- InSe(:Er) semiconductor. The current–voltage ( I – V ) and capacitance–voltage ( C – V ) characteristics of the diode have been determined at room temperature. The diode shows nonideal I – V behavior with an ideality factor greater than one. In addition, the I – V characteristics of the (MPP)/ n -InSe(:Er) device shows an improvement with an increased Φ b0 and a decreased ideality factor after the polymer melt processing step. The reverse bias C −2 – V characteristics of the diode shows a non-linear behavior.

Effect of temperature on the capacitance–frequency and conductance–voltage characteristics of polyaniline/p-Si/Al MIS device at high frequencies

Abstract A polyaniline/p-Si/Al MIS device has been fabricated by forming a polyaniline layer on Si by using the electrochemical polymerization method. The conductance–voltage and capacitance–frequency measurements have been performed as a function of temperature. The capacitance of the device decreased with increasing frequency. The increase in capacitance results from the presence of interface states. The peaks have been observed in the conductance curves of the device and attributed to the presence of an interfacial layer between polyaniline and p-Si. For each temperature, the plot of series resistance/voltage gave a peak. The voltage and temperature dependence of series resistance has been attributed to the particular distribution density of interface states and the interfacial insulator layer.

Cr/- and Fe/n-GaAs Schottky diodes: the stable current-voltage characteristic produced by high-temperature annealing

The electrical characteristics of Cr/- and Fe/liquid-encapsulated Czochralski (LEC)n-GaAs Schottky barrier diodes (SBDs) annealed at temperatures from 100 to C for 5 min and from 350 to C for 1 min have been investigated as a function of annealing temperature, with the use of current-voltage techniques. For Cr/n-GaAs SBDs, the Schottky barrier height and ideality factor n values range from 0.57 eV and 1.10 (for the as-deposited sample) to 0.80 eV and 1.10 (for C annealing). The ideality factor values remain approximately unchanged up to C and increased to 1.28 at C . For Fe/n-GaAs SBDs, the and n values range from 0.60 eV and 1.06 (for the as-deposited sample) to 0.78 eV and 1.08 (for C annealing). After C annealing, while the n values of the Fe/n-GaAs SBDs remain approximately unchanged between 1.10 and 1.12 up to C annealing, the value decreased with increasing temperature and became 0.75 at C (n = 1.11) and 0.73 at C (n = 1.20). It has been seen that the Cr/- and Fe/LECn-GaAs contacts are thermally stable under annealing up to C.

Thermal stability of Cr-Ni-Co alloy Schottky contacts on MBE -GaAs

The thermal stability of the Schottky barrier height of Cr-Ni-Co alloy Schottky contacts on an MBE n-GaAs substrate has been investigated using current-voltage (I-V) and capacitance-voltage (-V) techniques after thermal annealing for 5 min in an atmosphere at several temperatures in the 200-C range. It has been found that the value of (0.83 or 0.84 eV) remains constant up to C in the forward I-V mode. Because of the presence of an interfacial layer between the alloy contact and GaAs, an ideality factor value of 1.31 was obtained for as-deposited samples. This value decreases to 1.18 with increasing annealing temperature up to C. At annealing temperatures above C, the ideality factor n starts to increase. This has been explained in terms of the presence of different metallic-like phases produced by chemical reactions between the alloy and GaAs because of the annealing process. The (C-V) values obtained from the reverse-bias -V curves of the as-deposited and annealed diodes at 1 MHz are in the range 0.96-1.09 eV. The difference (0.13-0.26 eV) between (C-V) and the (I-V) is in close agreement with values reported in literature.