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Internal Electric Field (internal + electric_field)
Selected AbstractsEffect of Traps on Carrier Injection and Transport in Organic Field-effect TransistorIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 4 2010Martin Weis Non-member Abstract This study illustrates effect of traps on the charge injection and transport in the organic field-effect transistor (OFET). Here are included silicon nanoparticles (NPs) on a semiconductor-gate insulator interface, which work as trapping centers of charge carriers. Charge transport and injection phenomena are investigated by electrical measurements in presence of traps with designed densities. We find that OFETs with a low concentration of intrinsic carriers, such as a pentacene, are extremely sensitive to the internal electric fields. A significant threshold voltage shift due to trapped charge is observed, with a possibility to tune it by controlling the NP density. We demonstrate that the NP film can serve to design the amount of the accumulated charge in OFET and thus change the space-charge-limited conditions to the injection-limited conditions. A detailed analysis of pentacene OFET based on dielectric properties and the Maxwell-Wagner model reveals the internal electric field created by NPs. Additionally, the effect of NPs is discussed with respect to effective mobility, and its decrease is related to deceleration of carrier propagation by the trapping effect as well as low injection due to the increase of the carrier injection barrier by the internal field. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Depth profiling of optical and vibrational properties in GaN/AlN quantum dot superlatticesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2009A. Cros Abstract Spatially resolved confocal ,-Raman and ,-photoluminescence experiments were performed to analyze the vibrational and optical properties of GaN/AlN quantum dots as a function of depth. Two approaches have been followed. First, spectra were taken by defocusing the microscope objective at various depths on the sample surface. In a second set of experiments a bevel at an angle of 20° with respect to the surface normal was prepared by mechanical polishing of the surface, and spectra were taken across the bevel. The E2h vibrational modes ascribed to the GaN QDs and the AlN spacer redshift towards the surface, indicating the progressive relaxation of the QDs and a considerable increase of the tensile strain in the AlN spacer. The photoluminescence is found to blueshift and narrow towards the surface. This behaviour is ascribed to the decrease of the QD internal electric field as a consequence of the relaxation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth of GaN quantum dots on nonpolar A -plane SiC by molecular-beam epitaxyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2006S. Founta Abstract We report on A -plane GaN quantum dots in AlN, grown on A -plane 6H SiC substrates by plasma-assisted molecular-beam epitaxy. AFM imaging revealed a strong alignment of the dots along the [100] direction that we correlated with the anisotropic morphology of the AlN buffer layer. A vertical correlation of these dots was evidenced by high resolution transmission electron microscopy on superlattice samples with an AlN spacer thickness of 5 nm. Time-resolved spectroscopy performed on both C -plane and A -plane samples revealed much shorter radiative lifetimes for the A -plane dots, indicating a strong reduction of the internal electric field with respect to the one present in their C -plane counterparts. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Asymmetric barrier composition GaN/(Ga,In)N/(Al,Ga)N quantum wells for yellow emissionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Benjamin Damilano Abstract It is shown that by using asymmetric barrier composition GaN - (Ga,In)N (GaInN) - (Al, Ga)N (AlGaN) multiple quantum wells it is possible to redshift the room temperature photoluminescence wavelength from 503 nm (blue-green) to 577 nm (yellow) when the Al composition in the AlGaN barrier increases from 0 to 0.15. This is obtained without modifying the GaInN QW composition and thickness. This effect is attributed to an increase of the internal electric field inside the GaInN QW originating to additional polarization charges at the AlGaN - GaN and GaInN - AlGaN interfaces. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Discrete luminescence bands in AlGaN-based quantum wellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Hideaki Murotani Abstract The excitation-power-density dependent photoluminescence (PL) spectra have been studied for AlGaN-based quantum wells (QWs) with a well-layer thickness of 2, 4, and 6 nm. With increasing excitation-power density, an additional luminescence line was observed at the higher energy side of an initial luminescence line for the QWs with the well-layer thickness of 4 and 6 nm. The additional line also shifted toward higher energy side with further increasing excitation-power density. It was found from a theoretical calculation of the transition energy under applied electric field that an energy difference between the additional and the initial lines agreed with an energy separation for a well-layer-thickness variation of 2 monolayer for each QW. Therefore, these observations indicated that in the QWs with the well-layer thickness of 4 and 6 nm, the screening of the internal electric field occurred effectively after the saturation of localized states caused by the interface disorder. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature dependence of carrier traps in high sensitivity HARP photoconductive filmPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2009Yuji Ohkawa Abstract Amorphous selenium (a-Se) avalanche multiplication photoconductive film, what we call HARP (high-gain avalanche rushing amorphous photoconductor) photoconductive film, has been investigated for the purpose of reporting breaking news at night and producing nature and science programs. The purpose of our work is to develop more sensitive HARP films with high reliability. 15-,m-thick HARP film with an avalanche multiplication factor of about 200 that is thicker and more sensitive than the previous 8-,m-thick one has been studied. However, the thick film has a problem that defects easily occurred during shooting of intense spot lights. The defects are caused by trapped electrons which makes an enhanced internal electric field around the incident light side interface of the film. Defects are suppressed by operating the film at high temperatures, because the thermal energy releases the trapped electrons. This paper describes the relationship between the defect occurrence and the temperature dependence of carries trap in the film. To investigate it, the defect occurrence and dark current characteristics were measured. As a result, it was found that the number of released electrons exceeds that of trapped ones at temperatures over 28.5 °C and that defect occurrence is suppressed by operating the film at over 27.5 °C. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fabrication and optical properties of nano-structured semipolar InGaN/GaN quantum wells on c-plane GaN templatePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008Hongbo Yu Abstract High density self-assembled nanostructured semipolar (NSSP) GaN pyramids are fabricated based on c-plane GaN template by in situ silane treatment followed by high temperature treatment. Semipolar InGaN/GaN multiple quantum wells (MQWs) were subsequently grown on the NSSP GaN. Optical properties of the MQWs were studied by temperature- dependent and excitation density varied photoluminescence. It was found that the internal electric field in the NSSP MQWs were remarkably reduced in comparison with planar c-plane MQWs. The internal quantum efficiency of the NSSP MQWs was measured to be > 30% which showed potential applications in III-nitride light emitters. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Observation of the second-nearest-neighbor Bloch oscillation in a GaAs/AlAs superlatticePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008T. Hasegawa Abstract We have systematically investigated the quantum beat of the miniband excitons and the Bloch oscillation in the Wannier-Stark (WS) localization as a function of applied bias voltage in a GaAs (6.8 nm)/AlAs (0.9 nm) superlattice embedded in a p - i - n diode structure. The coherent dynamics behaviors were detected with a reflection-type pump-probe technique. We clearly observed the transformation process from the miniband-exciton quantum beat to the Bloch oscillation with an increase in applied bias voltage producing an internal electric field. The noteworthy finding is the fact that the Bloch oscillation with the frequency of vBO = 2eFD /h appears in a weak localization regime in addition to the usual Bloch oscillation with vBO = eFD /h in a strong localization regime, where F is the electric field, and D is the superlattice period. The frequency of 2eFD /h indicates that the newly observed Bloch oscillation is due to the wave-packet motion in the second-nearest-neighbor space range. The results described above are explained by the electric-field-strength dependence of the envelope-function localization, which is estimated from the envelope-function profile calculated by a transfer-matrix method and the excitonic transitions observed by electroreflectance spectroscopy. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The evolution of the electric field in an optically excited semiconductor superlatticePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2005Alvydas Lisauskas Abstract We report on time-resolved photocurrent spectroscopy of an intrinsic GaAs/Al0.3Ga0.7As superlattice subsequent to femtosecond optical excitation. Information on the spatio-temporal evolution of the densities of electrons and holes and on the internal electric field is obtained by tracing Wannier-Stark photocurrent spectra as a function of delay time for various bias fields and pump excitation intensities. The experimental results are supplemented by simulations. We employ the combined information to define the conditions to be met for succesful pump-probe Bloch gain experiments. In particular, we find that field screening sets on upper limit for the carrier density of 1016 cm,3, and that the time window during which gain should be found is defined by the duration of the sweep-out of the optically injected electrons from the superlattice which occurs within about 10 ps after excitation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photorefractive effect of ferroelectric liquid crystalsTHE CHEMICAL RECORD, Issue 1 2006Takeo Sasaki Abstract This paper reviews our recent work on the photorefractive effect of ferroelectric liquid crystals (FLCs). The photorefractive effect is defined as the optical modulation of the refractive index of a medium as a result of a variety of processes. The interference of two laser beams in a photorefractive material establishes a refractive index grating. This phenomenon enables the creation of different types of photonic applications. FLCs exhibit fast electric field response, and the orientation of the molecular axis of FLCs changes its direction according to the change in direction of the spontaneous polarization (Ps). When two laser beams interfere in a photoconductive FLC, an orientational grating is formed. The mechanism of the formation of the grating is based on the response of the Ps to the photoinduced internal electric field. The time of formation of the refractive index grating is significantly shorter in FLC materials. © 2006 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 6: 43,51; 2006: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20071 [source] The influence of an internal electric field upon protein crystallization using the gel-acupuncture methodACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2003N. Mirkin In this work, the influence of an internal electric field upon the crystallization of lysozyme and thaumatin is explored using a modified design of the gel-acupuncture setup. From a crystallographic point of view, the orientation of crystals that grow preferentially over different types of electrodes inside capillary tubes is also evaluated. Finally, the crystal quality and the three-dimensional structure of these proteins grown with and without the electric field influence are analyzed by means of X-ray diffraction methods. [source] Effect of Traps on Carrier Injection and Transport in Organic Field-effect TransistorIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 4 2010Martin Weis Non-member Abstract This study illustrates effect of traps on the charge injection and transport in the organic field-effect transistor (OFET). Here are included silicon nanoparticles (NPs) on a semiconductor-gate insulator interface, which work as trapping centers of charge carriers. Charge transport and injection phenomena are investigated by electrical measurements in presence of traps with designed densities. We find that OFETs with a low concentration of intrinsic carriers, such as a pentacene, are extremely sensitive to the internal electric fields. A significant threshold voltage shift due to trapped charge is observed, with a possibility to tune it by controlling the NP density. We demonstrate that the NP film can serve to design the amount of the accumulated charge in OFET and thus change the space-charge-limited conditions to the injection-limited conditions. A detailed analysis of pentacene OFET based on dielectric properties and the Maxwell-Wagner model reveals the internal electric field created by NPs. Additionally, the effect of NPs is discussed with respect to effective mobility, and its decrease is related to deceleration of carrier propagation by the trapping effect as well as low injection due to the increase of the carrier injection barrier by the internal field. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Photoinduced Faraday rotation in the magnetic semiconductor CdCr2Se4PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2004L. L. Golik Abstract A growth of the excitonic peak in the absorption spectrum and an enhancement of the Faraday rotation band (approximately 50% of the linear effect value) were induced by intensive radiation of Nd3+ -laser (h, = 1.17 eV) in ferromagnetic phase of magnetic semiconductor CdCr2Se4. The photoinduced effects increased during a pumping pulse and also with growth of pump intensity. In studies of the non-linear Faraday rotation a change of the spectral band shape was observed along with the growth of the rotation angle. The observed effects can be explained by the screening of internal electric fields existing in CdCr2Se4 crystals by photoexcited charge carriers. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pulsed layer growth of AlInGaN nanostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008Michael Jetter Abstract A pulsed layer growth mode in the metal-organic vapor phase epitaxy (MOVPE) was used to fabricate excellent quality AlInGaN nanostructures. The amount of material was varied, resulting in AlInGaN layer thicknesses between nominally 1.5 nm and 6 nm, respectively. We have analyzed the material properties by X-ray diffraction (XRD) as well as photoluminescence (PL) spectroscopy. The observed XRD-spectra and the PL intensity show the high quality of the deposited material. By analyzing the PL spectra we have found an energetic shift of the resonance lines from 2.65 eV to 3.33 eV with decreasing well thickness. We attribute this shift mainly to the presence of internal electric fields at the AlIn-GaN/GaN interface. Power-dependent and time resolved PL experiments confirm this observation. Comparing the luminescence at elevated temperatures, the pulsed layer epitaxy structures reveal a much higher intensity as the conventional grown samples. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||