Induced Charge Transport Research Articles

Solvent induced charge transport mechanism for conducting polymer at higher temperature

To elucidate the response of different solvents such as isopropyl-alcohol (IPA) and acetone for polyaniline-emeraldine-base (PANI), the charge transport mechanism is investigated as a function of temperature in the presence of different solvents. From SEM and XRD characterization, it is noted that each solvent improves the surface smoothness and negligible solvent traces were observed in the final thin-film devices. It is further observed that all devices follow space-charge-limited-current (SCLC) model to define their electrical responses. Conductivity was measured directly through four-probe method, while mobility was estimated from SCLC model and then both conductivity and mobility of PANI are compared with the given solvent at different temperatures. Similarly, it is also realized that the IPA solvent improves conductivity, mobility and degradation of PANI thin-film due to complex behaviour of solvent induced self-organization of molecular chains and reduction of residual traps as a function of temperature.

In Situ Electron Microscopy for Electrically Induced Charge Transport and Phase Transformation

In Situ Electron Microscopy for Electrically Induced Charge Transport and Phase Transformation

Superexchange Induced Charge Transport in Organic Donor–Acceptor Cocrystals and Copolymers: A Theoretical Perspective

Organic donor–acceptor (D–A) blending systems have displayed great potential in the application of organic optoelectronics. Conventionally, charge transport is not allowed along the stacking direct...

Transient and Enduring Electronic Resonances Drive Coherent Long Distance Charge Transport in Molecular Wires.

It is shown that the yields of oxidative damage observed in double-stranded DNA oligomers consisting of two guanines separated by adenine-thymine (A:T) n bridges of various lengths are reliably accounted for by a multistep mechanism, in which transient and nontransient electronic resonances induce charge transport and solvent relaxation stabilizes the hole transfer products. The proposed multistep mechanism leads to results in excellent agreement with the observed yield ratios for both the short and the long distance regime; the almost distance independence of yield ratios for longer bridges ( n ≥ 3) is the consequence of the significant energy decrease of the electronic levels of the bridge, which, as the bridge length increases, become quasi-degenerate with those of the acceptor and donor groups (enduring resonance). These results provide significant guidelines for the design of novel DNA sequences to be employed in organic electronics.

Layer dependent electrical transport in exfoliated graphene FETs under UV illumination

Controlled tunability of charge carriers is an intriguing technique to modify the electrical behavior of graphene. In this article, we report the photo-induced oxidation and its reversibility in single, bi and tri-layer graphene (S-B-TLG) devices by employing deep ultraviolet (DUV) light treatment in O2 and N2 atmosphere, respectively. Oxygen molecules in the presence of DUV light show dissociative adsorption onto the surface resulting a p-type carrier modulation in S-B-TLG devices. Treated graphene samples are characterized by Raman spectroscopy where blue-shift in G and 2D-peak positions is observed by DUV/O2 treatment without inclusion of any defect. The reverse effect of carrier modulation is observed when DUV/O2 treated samples are further studied in DUV/N2 atmosphere. The results of electrical measurements show the shift of Dirac point (DP) towards higher gate voltages (Vg > 0) which confirms a p-type carrier modulation in graphene whereas restoration of DP towards pristine state indicates the de-modulation of carriers in S-B-TLG devices. In addition, UV irradiation induced charge transport mechanism on graphene surface is further interpreted by employing density functional theory calculation and Bader charge transfer analysis. Such experimental and computational insights enhance the probability to understand the defect-free and controlled carrier modulation process, intensifying its applicability in electronic and optoelectronic devices.

Increase of power conversion efficiency in dye-sensitized solar cells through ferroelectric substrate induced charge transport enhancement

Ferroelectric functionalized dye-sensitized solar cells were fabricated by using a positively-poled LiNbO3 substrate coated with ITO (ITO-LiNbO3) as a collector electrode and demonstrated enhanced power conversion efficiency. Surface potential properties of TiO2 nanoparticle film coated on the ITO-LiNbO3 (TiO2/ITO-LiNbO3) examined by Kelvin probe force microscopy (KPFM) confirmed that a large electric field (a few 10 V/µm) generated from LiNbO3 can penetrate through the ITO layer and is applied to TiO2 film. This polarization-induced electric field leads to an increased photocurrent density by attracting and promoting electrons to direct transport through the mesoporous TiO2 network toward the collector electrode and a decreased charge recombination by facilitating electrons to pass through fewer boundaries of nanoparticles, resulting in high power conversion efficiency. The power conversion efficiency was enhanced by more than 40% in comparison with that without polarization-induced electric field. Incorporating functional ferroelectrics into photovoltaic cells would be a good strategy in improving photovoltaic performance and is applicable to other types of photovoltaic devices, such as perovskite solar cells.

Investigation of light induced charge transport properties in Dy2NiMnO6 perovskite based Schottky diode

ABSTRACTHere, we have discussed the charge transport phenomena through the interface formed by silver and double perovskite oxide Dy2NiMnO6 (DNMO). The charge carrier transport mechanism in Ag/DNMO junction under dark and illuminated conditions was analyzed on the basis of the thermionic emission theory of metal-semiconductor junction. The Schottky diode parameters like ideality factor, barrier potential height and series resistance of the freshly fabricated device were evaluated under dark and illuminated conditions. The results show significant improvements in the rectification ratio, barrier potential height and ideality factor of the device upon light illumination.

Light induced charge transport in La2NiMnO6 based Schottky diode

La2NiMnO6 (LNMO) thin film is prepared on fluorine doped tin oxide (FTO) coated glass by chemical solution deposition technique. The room temperature crystal structure of LNMO is determined using X-ray diffraction and Raman spectra. The band gap (∼1.33 eV) obtained using UV–visible absorption spectrum of LNMO film is found to be very close to the Shockley-Queisser band gap (∼1.34 eV) for a single junction solar cell. A FTO/LNMO/Au type Schottky device is fabricated to explore the photo physical properties of LNMO thin film. A significant change in the resistance, barrier potential height, effective mobility, conductivity, charge carrier density and carrier diffusion length is observed when the experiment is performed under dark and white light illuminations. The thermionic emission theory is used to analyze the charge transport mechanism in the material.

Suppressing the memory state of floating gate transistors with repeated femtosecond laser backside irradiations

We demonstrate that infrared femtosecond laser pulses with intensity above the two-photon ionization threshold of crystalline silicon induce charge transport through the tunnel oxide in floating gate Metal-Oxide-Semiconductor transistor devices. With repeated irradiations of Flash memory cells, we show how the laser-produced free-electrons naturally redistribute on both sides of the tunnel oxide until the electric field of the transistor is suppressed. This ability enables us to determine in a nondestructive, rapid and contactless way the flat band and the neutral threshold voltages of the tested device. The physical mechanisms including nonlinear ionization, quantum tunneling of free-carriers, and flattening of the band diagram are discussed for interpreting the experiments. The possibility to control the carriers in memory transistors with ultrashort pulses holds promises for fast and remote device analyses (reliability, security, and defectivity) and for considerable developments in the growing field of ultrafast microelectronics.

Role of the Insulating Fillers in the Encapsulation Material on the Lateral Charge Spreading in HV-ICs

High electric fields and temperatures in high-voltage ICs (HV-ICs) can induce charge transport phenomena in the encapsulation material leading to reliability test failures. In this paper, the resistivity of epoxy-based resins with insulating microfiller weight fraction exceeding 70% has been experimentally and theoretically investigated for the first time. Electrical conductivity has been measured at high temperature (150 °C) using both dielectric spectroscopy analysis on bulk samples and charge-spreading characterizations on a dedicated test chip with integrated charge sensors. The use of a charge sensor close to the internal HV metallization leads to results more pertinent with the active area of HV-ICs. Remarkably, both experiments show an unexpected increase and a significant variability of the electrical conductivity as the microfiller fraction is increased. The strong correlation between bulk and lateral experiments clearly indicates that those features should be attributed to the bulk material. Numerical simulations of diffusion phenomenon in mold structures with random arrangements of spherical microfillers demonstrate that the conductivity increase with filler content can be ascribed to the role of the epoxy/filler interfaces.

Acoustic charge transport induced by the surface acoustic wave in chemical doped graphene

A graphene/LiNbO3 hybrid device is used to investigate the acoustic induced charge transport in chemical doped graphene. The chemical doping of graphene via its physisorption of gas molecules affects the surface acoustic wave (SAW) charge carrier transport in a manner different from electric field drift. That transport induces doping dependent macroscopic acoustoelectric current. The chemical doping can manipulate majority carriers and induces unique acoustoelectric features. The observation is explained by a classical relaxation model. Eventually the device based on acoustoelectric current is proved to outperform the common chemiresistor for chemicals. Our finding provides insight into acoustic charge carrier transport during chemical doping. The doping affects interaction of carriers with SAW phonon and facilitates the understanding of nanoscale acoustoelectric effect. The exploration inspires potential acoustoelectric application for chemical detection involving emerging 2D nanomaterials.

Light induced charge transport property analysis of nanostructured ZnS based Schottky diode

In this report we have investigated the light sensing behavior and also discussed the induced charge transport phenomena through the junction made by aluminium and hydrothermally derived zinc-sulfide (ZnS). In this regards the structural, optical and electrical characterization of ZnS was performed well. The optical band gap energy (=3.68 eV) estimated from optical spectra and room temperature conductivity (0.49 × 10−6 S cm−1) measured from current–voltage characteristic explores the inorganic semiconductor behavior of the synthesized material. Depending upon the work function, aluminium (=4.4 eV) was preferred as metal contact to develop a potential barrier within the junction to study the underneath mechanism of charge transport through metal/inorganic-semiconductor interface. Moreover we have fabricated the sandwich structure ITO/ZnS/Al junction to study the effect of incident light on charge transport phenomena and demonstrated the potential applicability of the synthesized material to over crown the research on inorganic nano-semiconductor. The everbound charge transport phenomena within the device was analyzed by thermoionic emission theory. In searching its performance within light sensing electronic device we have deliberated the mobility-lifetime product, diffusion length and density of states (DOS) near Fermi level very aptly.

Influence of functional derivatives of an amino-coumarin/MWCNT composite organic hetero-junction on the photovoltaic characteristics

A layer of a coumarin derivative\\multiwall carbon nanotube (MWCNT) composite was sandwiched between an indium tin oxide (ITO) layer and a top metal electrode. This layer acted as the active hetero-junction (middle hetero-junction) in a triple hetero-junction organic solar cell. The composition of the organic material in the middle hetero-junction component, second from the ITO layer, was varied, keeping the weight percentage of the MWCNTs constant, to investigate the photovoltaic properties of the cell. The choice of amino-coumarin and its derivatives were dictated by the need for a high efficiency organic up-converter. Amino-coumarin is a two photon absorbing organic donor whereas CNTs are acceptors and ballistic charge transport media. For those reasons, amino-coumarin-CNT composite materials were selected as a photo active layer to will absorb the sub-band photons effectively. Additionally, the radial self-assembling of the CNTs inside the organic matrix (during synthesis) enhances the photovoltaic characteristics of the material. The photo induced charge transport mechanism between the MWCNTs and organics was analyzed using photo luminescence (PL) measurements. By the use of 15wt% of CNTs with the organics, more than 90% of the PL signal was quenched, indicating an ultrafast transport mechanism between the donor and acceptor materials.

Enhanced Sequential Carrier Capture into Individual Quantum Dots and Quantum Posts Controlled by Surface Acoustic Waves

Individual self-assembled quantum dots and quantum posts are studied under the influence of a surface acoustic wave. In optical experiments we observe an acoustically induced switching of the occupancy of the nanostructures along with an overall increase of the emission intensity. For quantum posts, switching occurs continuously from predominantly charged excitons (dissimilar number of electrons and holes) to neutral excitons (same number of electrons and holes) and is independent of whether the surface acoustic wave amplitude is increased or decreased. For quantum dots, switching is nonmonotonic and shows a pronounced hysteresis on the amplitude sweep direction. Moreover, emission of positively charged and neutral excitons is observed at high surface acoustic wave amplitudes. These findings are explained by carrier trapping and localization in the thin and disordered two-dimensional wetting layer on top of which quantum dots nucleate. This limitation can be overcome for quantum posts where acoustically induced charge transport is highly efficient in a wide lateral matrix-quantum well.

High current density, low threshold field emission from functionalized carbon nanotube bucky paper

Field emission studies of bucky paper of multiwalled carbon nanotubes (MWNTs), prepared after microwave (MW) assisted acid functionalization are reported along with a comparison with that of “as-grown” sample. MW treated bucky papers reveal an interesting linear field emission behavior in Fowler–Nordheim plot. The field emission currents at preset value are found to be remarkably stable over a period of more than 3 h sustaining current densities of 4.9 mA/cm2 and 8.5 mA/cm2 for “as-grown” and functionalized sample, respectively. The enhancement in the field emission due to functionalization has been discussed in terms of tip opening and defect induced charge transport caused by intershell and intertubular interaction.

Optically induced charge transport through submicron channels

We report on optically induced charge transport measurements through conducting submicron channels in AlGaAs/GaAs heterostructures. The channels are defined within a two-dimensional electron gas in a quantum well by chemical etching. By applying a voltage to a top gate, the channels can be depleted electrostatically. We present two different heterostructure designs and two processing techniques to build nanostructured optoelectronic detectors. We demonstrate the suitability of our devices for optically induced charge transport measurements in the mesoscopic regime.

Single event induced charge transport modeling of GaAs MESFETs

Two-dimensional computer simulations of charge collection phenomena in GaAs MESFETs have been performed for alpha and laser ionization. In both cases, more charge is collected than is created by the ionizing event. The simulations indicate that a bipolar transport mechanism (t<60 ps) and a channel modulation mechanism (t>40 ps) are responsible for this enhanced charge collection. The first mechanism is a bipolar type effect that injects charge into the bulk of the device and is collected at the drain due to the electric field. The second is a back channel turn-on mechanism that is associated with a positive hole density located beneath the channel and exists on a much longer time scale. These results show that electrons supplied by the source implant are responsible for charge collected at the drain in excess of any collected deposited charge.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Bistability and negative photoconductivity in optically induced real-space transfer.

Optically induced charge transport in a modulation-doped GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterostructure is studied theoretically. Intersubband excitation of electrons in the GaAs quantum well due to infrared absorption leads to their real-space transfer into the adjacent ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As layer. We derive a system of nonlinear model equations considering as relevant physical mechanisms the generation-recombination processes in GaAs, longitudinal and transverse dielectric carrier relaxation, as well as resonant and nonresonant tunneling across the interface, and analyze its behavior with the methods of nonlinear dynamics. We predict optoelectronic bistability associated with different photoconductive responses between the two locally stable steady states corresponding to different types of tunneling prevalent: the regime of dominant resonant-tunneling currents shows negative differential photoconductivity, whereas the nonresonant tunneling state is practically invariant with respect to changes of the IR intensity.

Light induced charge transport in doped LiNbO3and LiTaO3

Abstract The influence of special dopants on photovoltaic effects and photoconductivity of LiNbO3 and LiTaO3 single crystals is investigated. The measurements clearly indicate that the light induced transport properties can be completely controlled by dopants in suitable valence states. The results yield quantitative correlations thus permitting the derivation of simple models for various contributions to the charge transport.

Abstract: First wall materials problems in fusion reactors

Fusion reactors will utilize the reaction D + T → n (14.1 MeV) + He4(3.5 MeV) to generate heat for electric power production. Intense bremsstrahlung radiation as well as charged particles and neutrons will emanate from the burning plasma. Charged particles include fuel ions, alpha particles, and possible heavy ions previously ejected from the walls of the plasma chamber. First wall materials, which will operate at ∠900−1500 K, must retain their structural integrity in this severe thermal and radiation environment. In the case of the theta−pinch reactor first wall, which requires an insulating inner liner, electrical integrity must also be retained.First wall structural problems can be divided into surface and bulk phenomena. Surface phenomena may include such effects as sputtering, blistering, chemical erosion, and impurity desorption. 14 MeV neutron sputtering may prove to be a major problem; Kaminsky et al. 1 have found that niobium suffers extensive chunk−type sputtering under such bombardment. This phenomenon is not yet well characterized, however, and so the extent of the problem is uncertain. The formation and ablation of surface blisters due to ion bombardment has been studied by several investigators. It has been found that the implantation of monoenergetic, unidirectional hydrogen or helium ions can result in severe blistering of some materials, but the extent of the problem under reactor conditions has not yet been investigated. Chemical erosion (the formation and loss of new surface species under ion irradiation) is a potential problem area just now coming under investigation.2 A common characteristic of all surface effects (including desorption) is that accompanying material loss may result in plasma poisoning. Vernickel 3 has concluded that plasma contamination may be a more critical problem than wall thinning, at least in Tokamak fusion reactors. Ejection of eroded wall materials from the plasma back to the walls may prove to be a major problem, but its seriousness has not yet been evaluated in detail.Bulk first wall structural damage may be manifested as swelling, embrittlement, or other structural degradation, with loss of dimensional control or fracture as the possible consequence. Although the specific radiation environment of a fusion reactor first wall is not currently available to experimenters for swelling studies, projects are underway to develop irradiation techniques which simulate this environment. Progress in the development of swelling−resistant fission reactor metals by control of composition and microstructure 4 offers hope that swelling can also be alleviated in fusion reactor materials. Embrittlement is primarily a consequence of impurity pickup, either from transmutation or diffusion effects. Proposed first wall materials vary in their embrittlement tendencies; austenitic stainless steel, a metal under consideration for this application, is quite susceptible.5 Electrical problems for the first wall insulator of the pulsed theta−pinch reactor can also be divided into surface and bulk effects. Dielectric breakdown could be enhanced by local electric fields resulting from surface charging by the plasma or from photon−induced charge transport. However, the increased conductivity of insulators at elevated temperatures may preclude this possibility. Also, a neutral gas blanket between plasma and first wall is planned, to protect the wall from ion bombardment. Chemical reaction with hot fuel gases, structural metals, or coolants might result in formation of new surface or interface species with inferior dielectric properties. Electrical and structural surface effects for the theta−pinch reactor have been considered by Krakowski et al. 6 Bulk electrical degradation may result from the generation of free charge carriers by neutron or bremsstrahlung irradiation, or from changes in the concentration of traps and recombination centers. Because of the sequence of events during a plasma burn cycle, the insulator is not required to show good electrical properties during irradiation. 6 Thus, the kinetics of recovery of these properties after damage from the previous pulse (ten seconds earlier) must be determined before the magnitude of electrical damage problems can be assessed.