Current-voltage Characteristics Of Diodes Research Articles

Dependence of leakage current on dislocations in GaN-based light-emitting diodes

The reverse bias current-voltage (I–V) characteristics of GaN-based light-emitting diodes (LEDs) were investigated. The leakage current exhibits exponential dependence on the bias voltage with different exponents for various voltage ranges. The leakage current is closely related to the density of dislocations. The number of dislocations in GaN was determined by atomic force microscopy combined with hot H3PO4 etching. Dislocations with a screw component in the GaN films were found to have a strong influence on the reverse leakage current of LEDs. The dislocation electrical activity in GaN grown on c-plane sapphire is different from that in GaN grown on a-plane sapphire.

Carbon nanotube p-n junction diodes

We demonstrate a single-walled carbon nanotube p-n junction diode device. The p-n junction is formed along a single nanotube by electrostatic doping using a pair of split gate electrodes. By biasing the two gates accordingly, the device can function either as a diode or as an ambipolar field-effect transistor. The diode current–voltage characteristics show forward conduction and reverse blocking characteristics, i.e., rectification. For low bias conditions, the characteristics follow the ideal diode equation with an ideality factor close to one.

Dark currents in long wavelength infrared HgCdTe gated photodiodes

The fabrication of HgCdTe photodiodes using plasma-induced p-to-n type conversion for junction formation shows promise in improving array uniformity and device yields in comparison to more traditional fabrication technologies. Previously, characterization and analysis of the diode current-voltage (I–V) characteristics of fabricated devices have given indications that surface-leakage current mechanisms are limiting device performance. To further investigate the effectiveness of the surface passivation employed in the fabrication process, gated-diode structures have been fabricated. The gated-diode structure enables the semiconductor surface potential to be varied, thus allowing the characteristics of surface-leakage currents and their effect on device performance to be evaluated. The long wavelength infrared (LWIR) HgCdTe gated photodiodes used in this study have been characterized using I–V measurements for variable gate-bias voltage and variable temperature. Analysis of the experimental results indicates that plasma-induced type conversion produces an n (lightly doped)-on-p junction that is highly susceptible to a trapped positive charge in the passivation layer, which results in increased surface-tunneling currents. Modeling of the various dark-current mechanisms is used to show the effect on dark-current generation of the surface band bending induced by variations in surface potential. In addition, temperature-dependent I–V measurements and analysis have also been conducted.

Physical structure of molecular-beam epitaxy growth defects in HgCdTe and their impact on two-color detector performance

The flexible nature of molecular-beam epitaxy (MBE) growth is beneficial for HgCdTe infrared-detector design and allows for tailored growths at lower costs and larger focal-plane array (FPA) formats. Control of growth dynamics gives the MBE process a distinct advantage in the production of multicolor devices, although opportunities for device improvement still exist. Growth defects can inhibit pixel performance and reduce the operability in FPAs, so it is important to understand and evaluate their properties and impact on detector performance. The object of this paper is to understand and correlate the effects of macrodefects on two-color detector performance. We observed the location of single-crystal and polycrystalline regions on planar and cross-sectioned surfaces of two-color device structures when void defects were viewed by scanning electron microscopy (SEM). Compositional analysis via energy dispersive x-ray analysis (EDXA) of voids in the cross section showed elevated Te and reduced Hg when compared to defect-free growth areas. The second portion of this study examined the correlation of macrodefects with pixel operability and diode current-voltage (I–V) characteristics in mid-wavelength infrared (MWIR)/MWIR (M/M) and long wavelength infrared (LWIR)/LWIR (L/L) two-color devices. The probability of diode failure when a void is present is 98% for M/M and 100% for L/L. Voids in two-color detectors also impact diodes neighboring their location; the impact is higher for L/L detectors than M/M detectors. All void-containing diodes showed early breakdown in the I–V characteristics in one or both bands. High dislocation densities were observed surrounding voids; the high density spread further from the void for L/L detectors compared to M/M detectors.

Experimental verification on the origin of plateau-like current–voltage characteristics of resonant tunneling diodes

Current-voltage (I–V) characteristics of GaAs-based resonant tunneling diodes have been investigated in the presence of a perpendicular magnetic field. Electron resonant tunneling is strongly suppressed by the applied magnetic field, leading to peak current decreasing with increasing magnetic field. The observed plateau-like structures appear in negative differential resistance region on the I–V curves and are magnetic-field dependent. The plateau-like structures are due to the coupling between the energy levels in the emitter well and in the main quantum well.

Temperature dependence of electroluminescence of Er ions in tunnel diodes based on (111)Si:(Er, O)

Electroluminescence and current-voltage characteristics of tunnel diodes obtained by implantation of Er, O, and B ions into n-Si(111) with the subsequent heat treatment are investigated in a temperature range of 80–300 K in the breakdown mode. The observed increase in electroluminescence intensity with temperature for Er ions is caused by thermal emptying of the traps that captured the holes in the n-region of the diode at low temperatures. This emptying leads to a variation in the breakdown characteristics. It is shown that some of the traps at low temperatures retain the charge captured even after the voltage applied to the diode is switched off. This circumstance gives rise to the peculiar memory effect in the structures investigated.

Electrical-efficiency analysis of GaN-based light-emitting diodes with interdigitated-mesa geometry

We propose a novel method to analyze the current-voltage (I-V) characteristics of GaN-based light-emitting diodes (LEDs) with different p-type electrodemesa geometries. The electrical efficiency is analyzed by calculating the electric field under the quasi-coplanar electrodes of GaN-based LEDs. The experimental results for GaN-based LEDs of chip sizes of 350×350 µm2 and 1,000 × 1,000 µm2 with interdigitated fingers are compared. A good agreement is obtained between the experimental and theoretical electrical efficiency of the GaN LEDs with a chip size of 1,000×1,000 µm2. The current-crowding effect is analyzed by measuring the electroluminescence spectra of the devices. The result indicates that the current-crowding effect is largely reduced by increasing the number of interdigitated fingers. The electrical efficiency of a LED with a chip size of 1,000×1,000 µm2 can be also enhanced by increasing the number of interdigitated fingers, showing the advantages of GaN LED with interdigitated-mesa geometries.

Negative differential resistance in a reverse-biased diode with inhomogeneous base

The possibility of a negative differential resistance (NDR) region appearing in the reverse branch of the current-voltage characteristic of a semiconductor diode with a wide-bandgap layer in the base is theoretically predicted. The NDR formation is related to the fact that increasing reverse bias leads to a decrease in the thermal production of charge carriers in the narrow-bandgap part of the base (with a thickness on the order of the Debye screening length). It is shown that the NDR region appears, provided that the carrier lifetime in the diode base is determined by the Auger processes.

A reformulation of thermionic theory for vacuum diodes

Methods for predicting thermionic diode current–voltage characteristics have been in wide use for decades; however, serious limitations have been identified in the conventional formulations of thermionic theory. A reformulation of thermionic theory for vacuum diodes has been developed to improve predictive accuracy, to broaden the scope of application, and to establish a more consistent approach. Electron reflection effects and temperature dependent work functions are shown to be important considerations for thermionic diodes; consequently, the revised formulation focuses on proper treatment of these considerations. Revised equations are derived for predicting current densities, space charge, and electron cooling. In addition, equations are developed that provide energy–angle dependent current density spectra used to compute average transmission coefficients. An approach for computing space charge reflection parameters is also provided. Methods are given that permit application of the revised approach to inhomogeneous (patchy) electrode surfaces. A preliminary comparison shows that the predicted current–voltage characteristics using the revised formulations are in good agreement with test results for a prototype microminiature thermionic converter; whereas, more conventional formulations do not provide accurate predictions. Several new parameters are recommended to take advantage of the more precise methodology provided by the reformulation.

Anomalous current-voltage characteristics of polymer light-emitting diodes

Light-emitting diodes based on an alternating copolymer containing triphenylamine and phenylene units (TPA-PPA) were prepared, and electrically and optically characterized. The diode with a structure of indium tin oxide/TPA-PPV/Al exhibited a ``current anomaly'' phenomenon. We demonstrated that the ``current anomaly'' is caused by a reverse internal electric field owing to the reabsorption of electroluminescent light rather than the changes in the aluminum-doping concentration during operation.

Current-Voltage Characteristics of Organic Light-Emitting Diodes Depending on the Application of Forward-Reverse Bias Voltage

We have investigated current-voltage(I-V) characteristics of organic light-emitting diodes based on TPD/Alq 3 organics depending on the application of forward-reverse bias voltage. Luminance-voltage characteristics and luminous efficiency were measured at the same time when the I-V characteristics were measured. We have observed that the I-V characteristics were measured. We have observed that the I-V characteristics shows a current maxima at low voltage, which is not related to the emission from Alq 3 .

Current-Voltage Characteristics of Organic Light-Emitting Diodes Depending on the Application of Forward-Reverse Bias Voltage

We have investigated current-voltage(I-V) characteristics of organic light-emitting diodes based on TPD/Alq 3 organics depending on the application of forward-reverse bias voltage. Luminance-voltage characteristics and luminous efficiency were measured at the same time when the I-V characteristics were measured. We have observed that the I-V characteristics were measured. We have observed that the I-V characteristics shows a current maxima at low voltage, which is not related to the emission from Alq 3 .

Study of the correlation between low-frequency noise and the current-voltage characteristic of a GaAs Schottky-barrier diode

Correlation between low-frequency (1/f) noise and the current-voltage (I-V) characteristic of a beam-lead GaAs Schottky-barrier diode (SBD) is studied. It is shown that the ideality factor n of the I-V characteristic (and its increase) in the current range 10-4-10-3 A has the maximum correlation (the correlation coefficient kcor>0.9) with low-frequenvy noise measured at the same currents at frequencies 8-10 KHz, i.e., n is most sensitive to the series resistance of an SBD. At the same time, the values of n in the 10-6-10-5 A range usually do not exceed 1.1 and do not show correlation with low-frequency noise. The correlation is explained predominantly by the barrier-height nonuniformity over the Schottky-barrier contact.

Comparison of titanium and platinum Schottky barrier heights to Ga 0.47In 0.53As obtained from Franz Keldysh oscillations and Schottky diode characteristics

The Schottky barrier height of Ti and Pt contacts to Ga 0.47In 0.53As was measured using Franz Keldysh oscillations detected by electro absorption modulation, and compared to values obtained from the Schottky diode current voltage characteristics. Both methods reveal that the Schottky barrier height for holes in Pt contacts is 50–70 meV lower than in Ti contacts. The obtained barrier heights were used to calculate the specific contact resistance of Pt and Ti to p-type Ga 0.47In 0.53As. The results agree well with experimental data. A de-correlation method for improving the resolution of electro absorption data analysis is presented. An experimentally obtained correction factor for the measured electric field is introduced in order to account for a discrepancy between electro absorption theory and experiment.

Transparent p-n Heterojunction Thin Film Diodes

ABSTRACTTransparent p-n heterojunction diodes are fabricated using p-type CuYO2:Ca and n-type ZnO:Al thin films on a glass substrate coated with indium-tin oxide (ITO). The contact between the n-ZnO:Al / p-CuYO2:Ca heterojunction is found to be rectifying, while the ITO / ZnO:Al contact is ohmic. The typical ratio of forward to reverse current is 15 in the range -3 to 3V. The diode current-voltage characteristics are dominated by the flow of space charge limited current, which is ascribed to the existence of an insulating ZnO interfacial layer. The diode structure has a total thickness of 0.85 μm and an optical transmission of 40%-50% in the visible region.

Generalized model of recombination in inhomogeneous semiconductor structures

A generalized expression is obtained for the recombination velocity in structures with spatially separated electrons and holes. One stage of this process is tunneling. Under certain assumptions the general model yields the Shockley-Read recombination model and the tunneling recombination model. It is shown that an induced recombination effect may be observed in tunnel-coupled regions. An expression is obtained for the current-voltage characteristic of a surface-barrier diode in which tunneling recombination takes place. The theoretical results are compared with an experiment carried out using surface-barrier structures formed on gallium arsenide and thin As2Se3 films.

Electrical and structural properties of the swift heavy ion irradiated Au/n-GaAs schottky barrier diodes

Au/n-GaAs Schottky Barrier Diodes (SBDs) have been fabricated on LEC grown silicon doped (100) GaAs single crystals. The SBDs were irradiated using high energy (120 MeV) silicon ion with fluences of 1 × 10 11 and 1 × 1012 ions/cm2. Current-Voltage (I-V) characteristics of unirradiated and irradiated diodes were analyzed. The change in the reverse leakage current increases with increasing ion fluence. This is due to the irradiation induced defects at the interface and its increase with the fluence. The diodes were annealed at 573 and 673 K. to study the effect of annealing. The rectifying behavior of the irradiated (fluence of 1 × 1012 ions/cm12) SBDs improves upon as the annealing temperature increases and is attributed to the in situ self-annealing during irradiation. Scanning Electron Microscopic analysis was carried out on the irradiated samples to delineate the projected range and to observe defects.

Novel chaotic oscillator configuration using a diode-inductor composite

A general sinusoidal oscillator configuration is designed and then modified for chaos using a second-order nonlinear grounded diode-inductor composite. The configuration has an operating frequency that can be electronically tuned by varying the gain of an inverting amplifier stage. In addition to this amplifier, a single positive-type second generation current conveyor (CCII+), two noninverting integrators and two grounded resistors are required. The case where one of the integrators is replaced with an all-pass filter is investigated. Since the configuration is designed at a functional level, different circuit realizations are possible. Experimental results and PSpice simulations of a constructed implementation based on current feedback op amps are included. Numerical simulations of the derived chaotic mathematical models using a piecewise linear approximation of the diode current-voltage characteristics are also shown.

Consistent time-of-flight mobility measurements and polymer light-emitting diode current–voltage characteristics

We present time-of-flight mobility measurements and measured and calculated current–voltage (I–V) characteristics of structures fabricated using a soluble poly(p-phenylene vinylene) derivative. Time-of-flight measurements were used to determine the electric field dependent hole mobility. This mobility was then used, without adjustable parameters, to calculate the I–V characteristics of space-charge-limited, hole only devices. The measured and calculated I–V characteristics are in good agreement over five orders of magnitude in current. These results demonstrate that an electric field dependent mobility, without invoking trapping effects, provides an accurate description of hole transport in this polymer.

Negative differential resistance of a tunnel diode induced by an external microwave signal

An experimentally observed effect is described in which a section of negative differential resistance appears on the current-voltage characteristic of a tunnel diode exposed to an external microwave signal when the diode bias voltage in the absence of the microwave signal is substantially below the peak value. The measurements were made for signal frequencies in the range 25–140 GHz.