Current Injection Mechanism Research Articles

Approximating the electrical enhancement effects in a nano-patterned, injection-limited, single-layer organic light-emitting diode

Numerical analysis of the electrical effects accompanying nanocolumn patterning at the cathode-organic interface in an injection-limited, single-layer organic light-emitting diode (SLOLED) is conducted. We introduce a carrier-decoupled framework based on the Scott-Malliaras current injection mechanism in the double-sided, injection-limited current regime to simplify the multi-dimensional semiconductor equations in order to analyze the device function in the presence of a periodic nanocolumn array. A semi-analytical treatment is developed to solve the drift-diffusion equations. A common problem in SLOLEDs is unbalanced carrier currents arising from asymmetric injection and transport characteristics. The numerical results for the cathode nanopatterned device predict increased current injection with strongly asymmetrical current enhancement, which is shown to promote carrier injection parity in electron-deficient, single-layer devices by preferentially augmenting cathode-side injection current. Finally, the recombination current enhancement is attained and is shown to be increased by a factor of 8.52 and 3.00 when comparing the nanopatterned SLOLED device with planar devices of thicknesses equal to the unpatterned thickness and nanoimprint-thickness-reduced devices, respectively.

Proposal for tunnel-field-effect-transistor as ultra-sensitive and label-free biosensors

Tunnel field-effect-transistor (TFET) based biosensor is proposed, and it is shown that they can surpass by several orders, the performance of those based on conventional FET (CFET) and hence, can potentially revolutionize the biosensing applications. Analytical formula is derived for the sensitivity and response time to provide physical insights in terms of material bandgap and operation regime of the TFET biosensor for achieving optimal results. At the same time, rigorous numerical simulations have been performed in order to obtain accurate values of sensitivity for both biomolecule and pH sensing operations. The time dependent response of the biosensors has also been discussed through analytical and numerical solutions. It is shown that while the CFET biosensors suffer from fundamental limitations on the maximum sensitivity and minimum detection time achievable, TFET biosensors, with their fundamentally different current injection mechanism in the form of band-to-band tunneling, can overcome such limitations and lead to over four orders of magnitude higher sensitivity and over an order of magnitude lower response time.

Generating and routing light-bullets using slab waveguide arrays

Light-bullet routing and control is theoretically demonstrated in a slab waveguide architecture using a fully addressable electronic current injection mechanism for gain control. By exploiting gain mediated interactions between bullets, photonic NAND and NOR logic gates are produced on the same chip design. The robustness, simplicity, and control offered by light-bullets in slab waveguide architectures suggest that such devices should be seriously considered as candidates for technological development.

Mechanism of current injection in the process of wire electrical explosion

In the process of nanopowder production by the wire electrical explosion, the ablation of electrodes and the formation of micron-size particles are directly influenced by the way the current is injected into the metal wire from the electrodes. Through the channels which are provided by the contact between the electrodes and the wire ends, as well as the breakdown between them, a series of experiments of electrical explosion is carried out. Results show that the photocurrent detected by photodiodes at the wire ends almost occurs simultaneously with the circuit discharge current, however it at the central section lags behind the circuit discharge current obviously. The initial explosion product of the wire ends is liquid, and that of the other parts of wire is gas. Those results indicate that when the current folows into the contact, the phenomenon of gas discharge also occurs at the wire ends. Because the plasma provides another current path, the energy density of the wire ends is decreased. Hence, the wire ends cannot explode and form remainder on the electrodes. When the current flows into the breakdown, the electrodes ablated is slightly obvious, and there was no remainder on the electrodes.

Drain-Dependence of Tunnel Field-Effect Transistor Characteristics: The Role of the Channel

Because of its different current injection mechanism, a tunnel field-effect transistor (TFET) can achieve a sub-60-m/decade subthreshold swing at room temperature, which makes it very attractive in replacing a metal-oxide semiconductor field-effect transistor, particularly for low-power applications. It is well known that some specific TFET structures show a good drain current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> saturation in the output characteristics, whereas other structures do not. A detailed investigation, through extensive device simulations, of the role of the channel on the drain-potential dependence of double-gate TFET characteristics is presented in this paper for the first time. It is found that a good saturation of I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> is observed only for devices in which a thin silicon body is used. A relatively thick silicon body or gate-drain underlaps result in the penetration of the drain electric field through the channel, which does not allow the drain current to saturate, even at higher drain voltages.

Identifying electrical mechanisms responsible for functional failures during harsh external ESD and EMC aggression

For particular applications, system level stresses such as EMC stress or ESD (IEC61000-4-2) are directly applied to the integrated circuits with no external protections. Consequently, the integrated circuits have to be designed for reliability in order to stay alive but also to guarantee the normal operations during severe electrical aggressions. Unfortunately, the simulation of functional failures during severe ESD or EMC events remains very challenging for analog products due the frequency domain and to the high current injection mechanisms. This paper describes a test method to identify the design functions and the physical mechanisms that lead to functional failures when integrated circuits are submitted to system level stress.

Electrical characterization of a-Si:H(n)/c-Si(p) structure

In this study, n-type hydrogenated amorphous silicon (a-Si:H) was fabricated on p-type crystalline silicon (c-Si) substrates to obtain heterojunction diodes. The amorphous films were obtained by the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. Temperature dependent current–voltage ( I– V– T) measurements and investigation of the dc current injection mechanism of a-Si:H(n)/c-Si(p) device structure have been performed. The series resistance (4.6–8.2 Ω) values displayed nearly temperature independent behavior and the ideality factor varied between 2.7 and 1.6 in the temperature range 100–320 K. The forward bias I– V– T characteristics of c-Si/a-Si:H heterojunctions are found to behave like the Schottky junctions where carrier injection is especially influenced by the carrier generation-recombination in the junction interface formed on the amorphous side. The temperature dependent ideality factor behavior shows that tunneling enhanced recombination is valid rather than thermionic emission theory. In the frame of this model, characteristic tunneling energy and characteristic temperature are found to be 9 meV and 1900 K, respectively. It is concluded that fabricate n-type hydrogenated amorphous silicon is a preferable semiconductor material layer with low interface state density because the temperature dependent interface state density calculations give values of the order of 10 14 eV −1 cm −2.

Metal-nitride-oxide-semiconductor light-emitting devices for general lighting

The potential for application of silicon nitride-based light sources to general lighting is reported. The mechanism of current injection and transport in silicon nitride layers and silicon oxide tunnel layers is determined by electro-optical characterization of both bi- and tri-layers. It is shown that red luminescence is due to bipolar injection by direct tunneling, whereas Poole-Frenkel ionization is responsible for blue-green emission. The emission appears warm white to the eye, and the technology has potential for large-area lighting devices. A photometric study, including color rendering, color quality and luminous efficacy of radiation, measured under various AC excitation conditions, is given for a spectrum deemed promising for lighting. A correlated color temperature of 4800K was obtained using a 35% duty cycle of the AC excitation signal. Under these conditions, values for general color rendering index of 93 and luminous efficacy of radiation of 112 lm/W are demonstrated. This proof of concept demonstrates that mature silicon technology, which is extendable to low-cost, large-area lamps, can be used for general lighting purposes. Once the external quantum efficiency is improved to exceed 10%, this technique could be competitive with other energy-efficient solid-state lighting options.

Screening model of metallic nonideal contacts in the integer quantized Hall regime

In this work, we calculate the electron and the current density distributions both at the edges and the bulk of a two dimensional electron system, focusing on ideal and non-ideal contacts. A three dimensional Poisson equation is solved self-consistently to obtain the potential profile in the absence of an external magnetic field considering a Hall bar defined both by gates (contacts) and etching (lateral confinement). In the presence of a perpendicular magnetic field, we obtain the spatial distribution of the incompressible strips, taking into account the electron-electron interactions within the Thomas-Fermi approximation. Using a local version of Ohm's law, together with a relevant conductivity model, we also calculate the current distribution. We observe that the incompressible strips can reside either on the edge or at the bulk depending on the field strength. Our numerical results show that, due to a density poor region just in front of the contacts, the incompressible strips do not penetrate to the injection region when considering non-ideal contact configuration. Such a non-ideal contact is in strong contrast with the conventional edge channel pictures, hence has a strong influence on transport. We also take into account heating effects in a phenomenological manner and propose a current injection mechanism from the compressible regions to the incompressible regions. The model presented here perfectly agrees with the local probe experiments all together with the formation of hot-spots.

Mechanism of carrier injection in (Ni/Au)/p-AlxGa1−xN:Mg(≤x&amp;lt;0.1) Ohmic contacts

We report the mechanism of current injection in (Ni/Au)/p-AlxGa1−xN:Mg(0≤x&amp;lt;0.1) Ohmic contacts based on the temperature dependence of hole concentrations (p) and specific contact resistance (ρc). The injection mechanism is found to be thermionic emission in all cases. A model is developed to describe the temperature dependences of p and ρc for Mg concentrations from 1019 to 1020 cm−3. The model takes into account splitting in the valence band structure, hole activation energy, and Schottky barrier height. For GaN (AlGaN) these are found to be 132–140 (135–150) meV and 66–88 (84–93) meV, respectively.

Characterization of current injection mechanism in Schottky-barrier metal-oxide-semiconductor field-effect transistors

We discuss the carrier injection mechanism from source/drain to a channel in the on/off-state of Schottky-barrier silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistor by developing a refined extraction method for estimation of the Schottky-barrier height. This method is applied to validate the suggested mechanism by utilizing the dummy-gate in an underlap device with a thicker spacer and applying back-gate bias to SOI wafer. The results clearly show that the tunneled carriers from the drain side drive the off-state leakage current. In contrast with the conventional leakage path, the leakage current flows along the interfacial surface of the channel rather than a path underneath the channel.

Device Scaling Effects on Substrate Enhanced Degradation in MOS Transistors

AbstractThis paper analyzes in detail the substrate enhanced gate current injection mechanism and the resulting hot-carrier degradation in n-channel MOS transistors and compares the results with conventional channel hot carrier injection mechanism. The degradation mechanism is studied for different values of substrate voltage over a wide range of channel length and oxide thickness. Stress and charge pumping measurements are carried out to study the degradation under identical bias (gate, drain, substrate) and gate current condition. The influence of device dimensions on the gate injection efficiency and hot carrier degradation is also studied. Results show that the degradation under negative substrate voltage operation is strongly dependent on the transverse electric field and spread of the interface trap profile. The possible mechanism responsible for such trends is discussed. It is also found that, under identical gate current (programming time in flash memory cells), the degradation is less for higher negative substrate bias, which is helpful in realizing fast and reliable flash memories.

Current injection mechanism of organic thin-film electroluminescence devices

Current injection mechanism of organic thin-film electroluminescence devices

Current injection mechanism for porous-silicon transparent surface light-emitting diodes

We present a model for the injection of minority carriers into porous silicon films which results in visible dc electroluminescence. A thin interfacial dielectric region is postulated between the surface of the porous silicon layer and a transparent conductive oxide on the surface, which allows alignment of states between the two corresponding conduction bands of these materials under bias, and hence, overlap of electron wave functions and the passage of a tunneling current. Interface state densities are calculated and a parasitic nonradiative shunt current through such states is discussed.

Current–voltage characteristics of n-AlGaAs/p-GaAs heterojunction diodes

To understand the current injection mechanism in AlGaAs/GaAs heterojunction bipolar transistors (HBT’s), current–voltage characteristics of n-AlGaAs/p-GaAs heterojunctions have been studied for varying doping densities and as a function of temperature. The bulk space-charge recombination current studied in heterojunction diodes identical to emitter–base junction of an HBT has been found to be an order of magnitude smaller than that in GaAs homojunction diodes. It approximately varies as A(T) exp 20V where A(T) is a decreasing function of temperature. The nature of this current is similar to the excess current in tunnel diodes and is considered to be due to multistep tunneling followed by recombination. The tunneling nature of the current is established by the observed electroluminescence and the effect of varying doping densities. It is concluded that the surface currents normally dominate the base current and that they largely depend on the fabrication process and device geometries.

Dependence of negative resistance characteristics of avalanching MIM diodes on current injection mechanisms

Current-controlled negative resistance characteristics are computed for avalanche injection metal/insulator/metal diodes. Current injection is taken to occur by either Schottky thermionic emission or the Fowler-Nordheim tunneling mechanism. The results presented show that the diode negative resistance characteristics depend critically on both the magnitude and field dependance of injected currents.