Decrease In Ideality Factor Research Articles

Rectifying Characteristics and Transport Behavior in a Schottky Junction of CaCu3Ti4O12 and Pt

CaCu3Ti4O12 (CCTO) thin films were fabricated on ITO-covered MgO (100) substrates. The rectification characteristics were observed in the CCTO capacitance structure with Pt top electrodes at temperatures ranging from 150 K to 330 K, which are attributed to the formation of a Schottky junction between n-type semiconducting CCTO and Pt due to the difference of their work functions. At low forward-bias voltage, the current-voltage characteristics of the Schottky junction follow . A strong decrease in ideality factor with the increasing temperature is obtained by linear fitting at the low bias voltage.

The analysis of I– V characteristics of Schottky diodes by thermionic emission with a Gaussian distribution of barrier height

The current–voltage ( I– V) characteristics of Al/p-Si Schottky barrier diode (SBD) with native insulator layer were measured in the temperature range of 178–440 K. The estimated zero-bias barrier height Φ B 0 and the ideality factor n assuming thermionic emission (TE) theory have shown strong temperature dependence. Evaluation of the forward I– V data have revealed an increase of zero-bias barrier height Φ B 0 but the decrease of ideality factor n with the increase in temperature. The experimental and theoretical results of the tunneling current parameter E o against kT/ q were plotted to determine predominant current-transport mechanism. But the experimental results were found to be disagreement with the theoretical results of the pure TE, the thermionic-field emission (TFE) and the field emission (FE) theories. The conventional Richardson plot has exhibited non-linearity below 240 K with the linear portion corresponding to the activation energy of 0.085 eV and Richardson constant ( A * ) value of 2.48 × 10 −9 A cm −2 K −2 which is much lower than the known value of 32 A cm −2 K −2 for holes in p-type Si. Such behaviours were attributed to Schottky barrier inhomogeneities by assuming a Gaussian distribution of barrier heights (BHs) due to barrier height inhomogeneities that prevail at interface. Thus, the modified ln( I o / T 2) − q2σ o2/2 k 2 T 2 vs q/kT has plotted. Then A * was calculated as 38.79 A cm −2 K −2 without using the temperature coefficient of the barrier height. This value of the Richardson constant 38.79 A cm −2 K −2 is very close to the theoretical value of 32 A K −2 cm −2 for p-type Si. Hence, it has been concluded that the temperature dependence of the forward I– V characteristics of the Al/p-Si Schottky barrier diodes with native insulator layer can be successfully explained on the basis of TE mechanism with a Gaussian distribution of the barrier heights.

Current–voltage characteristics of Al/Rhodamine-101/ n-GaAs structures in the wide temperature range

The forward bias current–voltage ( I–V) characteristics of Al/Rhodamine-101/ n-GaAs structure have been investigated in the temperature range of 80–350 K. It has been seen a decrease in ideality factor ( n) and an increase in the zero-bias barrier height (BH) with an increase in temperature. It has been seen that such a behavior of the BH and n obey Gaussian distribution of the BHs due to the BH inhomogeneities at the metal/semiconductor (MS) interface. The very strong temperature dependence of ideality factor of the structure has shown that the current processes occurring in the organic layer at the MS interface would be a possible candidate such as trap-charge limited conduction in determining the current at the intermediate and high bias regimes. Furthermore, it has been show that the Rh101 can be used to vary effective BHs for the metal/GaAs Schottky diodes. As a result, it has been determined that the BH value for conventional Al/ n-GaAs SBD is remarkably higher than our own values of 0.68 eV obtained for the Al/Rh101/ n-GaAs at 290 K.

Electrical characterization of the polyaniline/p-silicon and polyaniline titanium dioxide tetradecyltrimethylammonium bromide /p-silicon heterojunctions

Au/PANI/p-Si/Al and Au/PANI TiO 2 TTAB/p-Si/Al heterojunctions have been fabricated by spin coating of soluble polyaniline (PANI) and PANI titanium dioxide (TiO 2) tetradecyltrimethylammonium bromide (TTAB) on the chemically cleaned p-Si substrates. The thicknesses of the polymeric films have been determined by a profilometer. The current–voltage ( I–V) characteristics of the heterojunctions have been obtained in the temperature range of 98–258 K. These devices have showed the rectifying behavior such as diode. The I–V characteristics of the devices have been analyzed on the basis of the standard thermionic emission theory at low forward bias voltage regime. It has been shown that the values of ideality factor decrease while the values of barrier height increase with increasing temperature. This temperature dependence has been attributed to the presence of barrier inhomogeneities at the organic/inorganic semiconductor interface. Furthermore, analysis of the double logarithmic I–V plots at higher forward bias voltages at all temperatures indicates that transport through the organic thin film is explained by a space-charge-limited current process characterized by exponential distribution of traps within the band gap of the organic film. The total concentration of traps has been found to be 3.52 × 10 14 cm − 3 and 3.14 × 10 15 cm − 3 for PANI and PANI TiO 2 TTAB layer, respectively.

High-temperature characteristics of AlxGa1−xN/GaN Schottky diodes

High-temperature characteristics of the metal/AlxGa1−xN/GaN M/S/S (M/S/S) diodes have been studied with current–voltage (I–V) and capacitance–voltage (C–V) measurements at high temperatures. Due to the presence of the piezoelectric polarization field and a quantum well at the AlxGa1−xN/GaN interface, the AlxGa1−xN/GaN diodes show properties distinctly different from those of the AlxGa1−xN diodes. For the AlxGa1−xN/GaN diodes, an increase in temperature accompanies an increase in barrier height and a decrease in ideality factor, while the AlxGa1−xN diodes are opposite. Furthermore, at room temperature, both reverse leakage current and reverse breakdown voltage are superior for the AlxGa1−xN/GaN diodes to those for the AlxGa1−xN diodes.

Characterization of electrical parameters of a PtSi/p-Si Schottky barrier detector

The current-voltage characteristics of a PtSi/p-Si Schottky barrier diode was measured at the temperature of 85K and from the forward bias region of the I-V curve, the electrical parameters of the diode were measured by three methods. The results obtained from the two methods which considered the series resistance were in close agreement with each other and from them barrier height (Φb), ideality factor (n) and series resistance (Rs) were found to be 0.2045eV, 2.877 and 14.556KΩrespectively. By measuring the I-V characteristics in the temperature range of 85-136K the electrical parameters were observed to have strong dependency on temperature. The increase of barrier height and decrease of ideality factor with increasing temperature is attributed to the existence of barrier height inhomogeneities in the silicide-semiconductor structure.

Electrical characterization of 100 MeV heavy ion irradiated Au/p-Cu1.4S Schottky barrier diodes

Interface states play a vital role in Fermi-level pinning in Schottky barrier diodes. Here, we have modified the surface of copper sulfide by using 100 MeV Au8+ swift heavy ions. On this modified surface, a Schottky diode was fabricated using gold metal. This leads to an interface with different ‘interface states’, affecting the charge transport and diode properties. I–V measurements showed that the current decreases with increase in ion fluence from 1011 to 1013 ions cm−2, and barrier height increases while ideality factor decreases. These results are explained by taking into account the presence of free copper at the surface and grain boundaries of copper sulfide thin films and its diffusion into the matrix.

Deep saturation of junction voltage at large forward current of light-emitting diodes

The dependences of series resistance, ideality factor, and junction voltage of light-emitting diodes (LEDs) on applied voltage or current were characterized accurately using alternating current (ac) behavior combined with I-V plot (acIV method). The deep saturation of junction voltage and simultaneous decrease of ideality factor of LEDs at large forward current, which imply the pinning of quasi-Fermi levels, were observed. Comparing with our recent study of the similar phenomenon of laser diodes, in which the junction voltage jumps abruptly to a saturated value at lasing threshold, the changes of junction voltage of LEDs are gradual. In addition, the decrease of series resistance with the increasing current and the negative capacitance effect of LEDs were also investigated.

Effect of Cryogenic Temperature Deposition of Various Metal Contacts on Bulk Single-Crystal n-Type ZnO

The effect of cryogenic temperatures during metal deposition on the contact properties of Pd, Pt, Ti, and Ni on bulk single-crystal n-type ZnO has been investigated. Deposition at both room and low temperature produced contacts with Ohmic characteristics for Ti and Ni metallizations. By sharp contrast, both Pd and Pt contacts showed rectifying characteristics after deposition with barrier heights between 0.37 eV and 0.69 eV. Changes in contact behavior were measured on Pd to anneal temperatures of ∼300 °C, showing an increase in barrier height along with a decrease in ideality factor with increasing annealing temperature. This difference with annealing temperature is in sharp contrast to previous results for Au contacts to ZnO. There were no differences in near-surface stoichiometry for the different deposition temperatures; however, low temperature contacts demonstrated some peeling/cracking for Pt and Pd.

Temperature-dependent electrical characteristics of bulk GaN Schottky rectifier

The temperature-dependent electrical characteristics of Schottky rectifiers fabricated with a SiO2 field plate on a freestanding n− gallium nitride (GaN) substrate were reported in the temperature range of 298–473K. The Schottky barrier heights evaluated from forward current-voltage measurement revealed an increase of Schottky barrier height and series resistance but a decrease of ideality factor (n) with increasing temperature. However, the Schottky barrier heights evaluated from capacitance-voltage measurement remained almost the same throughout the temperature range measured. The Richardson constant extrapolated from ln(J0∕T2) vs 1∕T plot was found to be 0.029Acm−2K−2. A modified Richardson plot with ln(J0∕T2) vs 1∕nT showed better linearity, and the corresponding effective Richardson constant was 35Acm−2K−2. The device showed a high reverse breakdown voltage of 560V at room temperature. The negative temperature coefficients were found for reverse breakdown voltage, which is indicative of a defect-assisted breakdown.

Fabrication of low-cost n-Sb2S3/p-Ge heterojunction solar cells

A novel method to fabricate low-cost n-Sb2S3/p-Ge heterojunction solar cells by chemical deposition is reported. It has been observed that, in the case of n-Sb2S3 films chemically deposited with silicotungstic acid on (111) oriented single-crystalline p-Ge and annealed, the heterojunction solar cell properties are considerably improved. Dark current-voltage (I-V) measurements (in the range 298-380 K) on n-Sb2S3/p-Ge and siligotuxngstic-acid-deposited n-Sb2S3/p-Ge heterojunction devices showed an increase in barrier height ( phi b) from 0.65 to 0.89 eV, a decrease in ideality factor (n) from 2.21 to 1.38 and in reverse saturation current density (J0) from 6.27*10-7 to 3.8*10-9 A cm-2. Capacitance-voltage (C-V) studies at 1 MHz showed higher values of phi b for the improved device. Under AM1 (air mass 1) illumination, the improved junction showed an efficiency ( eta ) of about 7.3% without any antireflection coating whereas the n-Sb2S3 films deposited without silicotungstic acid on p-Ge showed eta approximately=2.4%.

Improved Au/n-GaAs Schottky barriers due to Ru surface modification

Au/n-GaAs Schottky diodes were studied before and after Ru surface modification and characterised by current-voltage ( I- V) measurements between 108 and 358 K. An increase in barrier height ( φ Bn ) from 0.80 to 0.92 V, decrease in ideality factor ( n) from 1.34 to 1.16 and in reverse saturation current density ( J 0) from 2.1 × 10 −8 to 1.57 × 10 −10 A cm −2 were observed. The values of the effective Richardson constant were also evaluated. Capacitance-voltage ( C- V) studies at 303 K showed larger values of φ Bn , reasons for which are discussed. The effect of Ru modification on the surface of GaAs is considered on the basis of these observations.

Surface-modified CdTe PEC solar cells

The effect of ruthenium surface modification is shown to improve considerably the properties of p-CdTe PEC solar cells. The dark I–V characteristic shows a decrease in J 0 from 2.8 × 10 −7 A cm −2 to 5.1 × 10 −8 A cm −2 and a decrease in ideality factor n from 2.72 to 1.54. Under AM 1 illumination V oc increased from 0.63 to 0.92 V vs. NHE, J sc from 2.17 mA cm −2 to 3.23 mA cm −2 and fill factor FF from 0.38 to 0.48. The minority carrier diffusion length L n is shown to increase from 0.72 μm to 0.99 μm after ruthenium modification. The maximum current density obtainable is limited by material resistivity.