The Experts below are selected from a list of 31080 Experts worldwide ranked by ideXlab platform
Yannmichel Niquet - One of the best experts on this subject based on the ideXlab platform.
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Stark Effect in gan aln nanowire heterostructures influence of strain relaxation and surface states
Physical Review B, 2010Co-Authors: Camacho D Mojica, Yannmichel NiquetAbstract:We model the quantum confined Stark Effect in AlN/GaN/AlN heterostructures grown on top of [0001]-oriented GaN nanowires. The pyro- and piezoelectric field are computed in a self-consistent approach, making no assumption about the pinning of the Fermi level, but including an explicit distribution of surface states which can act as a source or trap of carriers. We show that the pyro- and piezoelectric field bends the conduction and valence bands of GaN and AlN and transfers charges from the top surface of the nanowire to an electron gas below the heterostructure. As a consequence, the Fermi level is likely pinned near the valence band of AlN at the top surface. The electron gas and surface charges screen the electric field, thereby reducing the Stark Effect. The efficient strain relaxation further weakens the piezoelectric polarization. We compute the electronic properties of the heterostructures with a sp3d5s* tight-binding model, and compare the theoretical predictions with the available experimental data.
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Stark Effect in gan aln nanowire heterostructures influence of strain relaxation and surface states
Physical Review B, 2010Co-Authors: Camacho D Mojica, Yannmichel NiquetAbstract:We model the quantum confined Stark Effect in AlN/GaN/AlN heterostructures grown on top of [0001]-oriented GaN nanowires. The pyroelectric and piezoelectric field are computed in a self-consistent approach, making no assumption about the pinning of the Fermi level, but including an explicit distribution of surface states which can act as a source or trap of carriers. We show that the pyroelectric and piezoelectric field bends the conduction and valence bands of GaN and AlN and transfers charges from the top surface of the nanowire to an electron gas below the heterostructure. As a consequence, the Fermi level is likely pinned near the valence band of AlN at the top surface. The electron gas and surface charges screen the electric field, thereby reducing the Stark Effect. The efficient strain relaxation further weakens the piezoelectric polarization. We compute the electronic properties of the heterostructures with a $s{p}^{3}{d}^{5}{s}^{\ensuremath{\ast}}$ tight-binding model and compare the theoretical predictions with the available experimental data.
Camacho D Mojica - One of the best experts on this subject based on the ideXlab platform.
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Stark Effect in gan aln nanowire heterostructures influence of strain relaxation and surface states
Physical Review B, 2010Co-Authors: Camacho D Mojica, Yannmichel NiquetAbstract:We model the quantum confined Stark Effect in AlN/GaN/AlN heterostructures grown on top of [0001]-oriented GaN nanowires. The pyro- and piezoelectric field are computed in a self-consistent approach, making no assumption about the pinning of the Fermi level, but including an explicit distribution of surface states which can act as a source or trap of carriers. We show that the pyro- and piezoelectric field bends the conduction and valence bands of GaN and AlN and transfers charges from the top surface of the nanowire to an electron gas below the heterostructure. As a consequence, the Fermi level is likely pinned near the valence band of AlN at the top surface. The electron gas and surface charges screen the electric field, thereby reducing the Stark Effect. The efficient strain relaxation further weakens the piezoelectric polarization. We compute the electronic properties of the heterostructures with a sp3d5s* tight-binding model, and compare the theoretical predictions with the available experimental data.
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Stark Effect in gan aln nanowire heterostructures influence of strain relaxation and surface states
Physical Review B, 2010Co-Authors: Camacho D Mojica, Yannmichel NiquetAbstract:We model the quantum confined Stark Effect in AlN/GaN/AlN heterostructures grown on top of [0001]-oriented GaN nanowires. The pyroelectric and piezoelectric field are computed in a self-consistent approach, making no assumption about the pinning of the Fermi level, but including an explicit distribution of surface states which can act as a source or trap of carriers. We show that the pyroelectric and piezoelectric field bends the conduction and valence bands of GaN and AlN and transfers charges from the top surface of the nanowire to an electron gas below the heterostructure. As a consequence, the Fermi level is likely pinned near the valence band of AlN at the top surface. The electron gas and surface charges screen the electric field, thereby reducing the Stark Effect. The efficient strain relaxation further weakens the piezoelectric polarization. We compute the electronic properties of the heterostructures with a $s{p}^{3}{d}^{5}{s}^{\ensuremath{\ast}}$ tight-binding model and compare the theoretical predictions with the available experimental data.
John Howard - One of the best experts on this subject based on the ideXlab platform.
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motional Stark Effect measurements of the local magnetic field in high temperature fusion plasmas
Journal of Instrumentation, 2015Co-Authors: R C Wolf, John Howard, A Dinklage, A Bock, O Ford, R Reimer, A Burckhart, J Hobirk, M Reich, J StoberAbstract:The utilization of the Motional Stark Effect (MSE) experienced by the neutral hydrogen or deuterium injected into magnetically confined high temperature plasmas is a well established technique to infer the internal magnetic field distribution of fusion experiments. The different properties of the Stark multiplet allow inferring, both the magnetic field strength and the orientation of the magnetic field vector. Besides recording the full MSE spectrum, several types of polarimeters have been developed to measure the polarization direction of the Stark line emission. To test physics models of the magnetic field distribution and dynamics the accuracy requirements are quite demanding. In view of these requirements, the capabilities and issues of the different techniques are discussed, including a newly developed Imaging MSE system which has been tested on the ASDEX Upgrade tokamak.
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the prototype imaging motional Stark Effect diagnostic for asdex upgrade
Review of Scientific Instruments, 2015Co-Authors: O Ford, John Howard, R WolfAbstract:This paper presents the development and testing of the prototype Imaging Motional Stark-Effect (IMSE) diagnostic, designed for ASDEX upgrade. A detailed description of the core hardware, theory of operation, and application to complex MSE spectra are presented and analytical evaluation methods suitable for the required accuracy are developed. The diagnostic is tested with a MSE-like polarised spectrum to assess the accuracy of different modulation modes suggested in previous works. Each is found to have small systematic errors due to non-ideal Effects of the components, which must be carefully examined. In particular, the Effect of intrinsic contrast that results from imperfect parallelism of the birefringent plates is found to have a strong Effect. Methods to mitigate and correct for this are discussed. With the necessary corrections and calibrations, the accuracy of polarisation orientation is shown to be within ±0.2°. The Effect of finite ellipticity is examined and the possibility to measure this to an accuracy of ±2.0° is demonstrated. The system is shown to be insensitive to broadband polarised background light, temperature variations, and critically to variations in the details of the MSE spectrum.
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Snapshot-imaging motional Stark Effect polarimetry
Plasma Physics and Controlled Fusion, 2008Co-Authors: John HowardAbstract:Measurement of the motional Stark Effect (MSE) for Balmer alpha light emitted from heating or diagnostic neutral beams is a standard technique for estimating plasma toroidal current density in tokamaks. Most techniques typically rely on a determination of the polarization angle or relative intensities of the multiplet components which are spectrally resolved using either an array of interference filters or a high-throughput grating instrument. Neither of these approaches is amenable to two-dimensional MSE imaging. This paper proposes an alternative measurement scheme that is suitable for single snapshot two-dimensional imaging of the current distribution. This is achieved using a spectro-polarimeter that encodes the polarization and spectral information upon spatially orthogonal linear interference fringe patterns illuminated by the image of the Stark-shifted H-alpha emission from the neutral beam. The new technique opens the possibility to use synchronous detection methods and gated cameras to resolve the magnetic structure of periodic tokamak phenomena including sawteeth and magnetohydrodynamic activity.
James S. Harris - One of the best experts on this subject based on the ideXlab platform.
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Quantum-Confined Stark Effect in Ge/SiGe Quantum Wells on Si Substrate for Modulators
International Summer Session: Lasers and Their Applications, 2011Co-Authors: Xiaochi Chen, Yiwen Rong, Yijie Huo, Theodore I. Kamins, Ed Fei, Xi Liu, James S. HarrisAbstract:We investigate the growth and optical characterization of Ge/SiGe quantum wells on silicon substrate to exploit its strong quantum-confined Stark Effect (QCSE) for electroabsorption modulator in long wavelength regime. Further, we design and fabricate devices based on this approach and investigate the high-speed modulation performance of the device.
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Quantum-Confined Stark Effect in Ge/SiGe Quantum Wells on Si
IEEE Journal of Selected Topics in Quantum Electronics, 2010Co-Authors: Yiwen Rong, Yijie Huo, Marco Fiorentino, Theodore I. Kamins, Tomasz J. Ochalski, Michael Renne Ty Tan, Guillaume Huyet, James S. HarrisAbstract:In this paper, we present observations of quantum confinement and quantum-confined Stark Effect electroabsorption in Ge quantum wells with SiGe barriers grown on Si substrates. Though Ge is an indirect gap semiconductor, the resulting Effects are at least as clear and strong as seen in typical III-V quantum well structures at similar wavelengths. We also designed and fabricated a coplanar high-speed modulator, and demonstrated modulation at 10 GHz and a 3.125-GHz eye diagram for 30-?m-sized modulators.
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quantum confined Stark Effect in ge sige quantum wells on si for optical modulators
IEEE Journal of Selected Topics in Quantum Electronics, 2006Co-Authors: Yuhsuan Kuo, D.a.b. Miller, Theodore I. Kamins, Yong Kyu Lee, Shen Ren, Jonathan E Roth, James S. HarrisAbstract:We present observations of quantum confinement and quantum-confined Stark Effect (QCSE) electroabsorption in Ge quantum wells with SiGe barriers grown on Si substrates, in good agreement with theoretical calculations. Though Ge is an indirect gap semiconductor, the resulting Effects are at least as clear and strong as seen in typical III-V quantum well structures at similar wavelengths. We also demonstrate that the Effect can be seen over the C-band around 1.55-mum wavelength in structures heated to 90degC, similar to the operating temperature of silicon electronic chips. The physics of the Effects are discussed, including the Effects of strain, electron and hole confinement, and exciton binding, and the reasons why the Effects should be observable at all in such an indirect gap material. This Effect is very promising for practical high-speed, low-power optical modulators fabricated compatible with mainstream silicon electronic integrated circuits
B Gayral - One of the best experts on this subject based on the ideXlab platform.
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evidence for quantum confined Stark Effect in gan aln quantum dots in nanowires
Physical Review B, 2009Co-Authors: Julien Renard, R Songmuang, G Tourbot, Catherine Bougerol, B Daudin, B GayralAbstract:Semiconductor nanowires have the potential to outperform two-dimensional structures, for instance for light-emitting applications. However, the intrinsic fundamental properties of heterostructures in nanowires still remain to be assessed and compared to their two-dimensional counterparts. We show that polar GaN/AlN axial heterostructures in nanowires grown by plasma-assisted molecular-beam epitaxy are subject to a clear quantum-confined Stark Effect. However, the magnitude of this Effect is smaller than for two-dimensional structures due to the reduction in piezoelectric polarization that occurs thanks to elastic relaxation which is favored by the nanowire free surfaces. Moreover, we show by temperature-dependent photoluminescence measurement and single-photon correlation measurements that these heterostructures behave like quantum dots.
