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Thermal And Electrical Characteristics Of A Multilayer Thermionic Device, B. C. Lough, S. P. Lee, Z. Dou, R. A. Lewis, C. Zhang
Thermal And Electrical Characteristics Of A Multilayer Thermionic Device, B. C. Lough, S. P. Lee, Z. Dou, R. A. Lewis, C. Zhang
Chao Zhang
We report our recent experimental and numerical investigation into the thermal and electrical transport in GaAs-AlGaAs semiconductor multilayer structures. Electrical and thermal conduction measurements were performed on multilayer structures to determine the temperature gradient across the sample. AuGe was used for top contact metallisation, and an InGa eutectic for bottom substrate contact. Metallisation contacts were also grown directly onto the substrate in order to compare results with and without the device included. By using a variable load resistor connected in series with the device, we can accurately determine the current-voltage characteristics of the device. Thus the power input can be …
Optical Absorption In Terahertz-Driven Quantum Wells, X. W. Mi, J. C. Cao, C. Zhang
Optical Absorption In Terahertz-Driven Quantum Wells, X. W. Mi, J. C. Cao, C. Zhang
Chao Zhang
The optical absorption spectra in a quantum well driven both by an intense terahertz (THz) and by an optical pulse are theoretically investigated within the theory of density matrix. We found that the optical absorption spectra and the splitting of the excitonic peaks splitting can be controlled by changing the THz field intensity and/or frequency. The Autler–Towns splitting is a result of the THz nonlinear dynamics of confined excitons, which is in agreement with the experiments. In addition, the dependence of the optical absorption on the quantum well width and the carrier density is also discussed.
Two Colour Plasmon Excitation In An Electron-Hole Bilayer Structure Controlled By The Spin-Orbit Interaction, C. H. Yang, A. Wright, Feng Gao, C. Zhang, Z. Zeng, W. Xu
Two Colour Plasmon Excitation In An Electron-Hole Bilayer Structure Controlled By The Spin-Orbit Interaction, C. H. Yang, A. Wright, Feng Gao, C. Zhang, Z. Zeng, W. Xu
Chao Zhang
In recent years, the terahertz plasma effects in high-mobility electronic systems have attracted much attention theoretically and experimentally. Plasma excitation in the terahertz regime can be used for generation, detection, and frequency multiplication of terahertz radiation. A channel of a field-effect transistor with sufficiently high electron mobility can serve as a resonant cavity for the plasma oscillation. When the signal period is in the vicinity of the electron transit time, self-excitation of plasma oscillation can occur. If the typical plasma frequency is in the terahertz regime, the phenomenon can be used as a terahertz source.
Magnetoplasmon Emission Versus Landau-Level Scattering In Resonant Tunneling Through Double-Barrier Structures , C. Zhang, D. J. Fisher
Magnetoplasmon Emission Versus Landau-Level Scattering In Resonant Tunneling Through Double-Barrier Structures , C. Zhang, D. J. Fisher
Chao Zhang
We consider electron tunneling in a parallel magnetic field taking into account the electron-electron interaction. It is shown that a self-consistent treatment of the dynamical electron-electron interaction in resonant tunneling can lead to the proposed plasmon assisted resonant tunneling. Such magnetoplasmon assisted resonant tunneling gives rise to satellite peaks or shoulders in the tunneling current. At low temperatures, only magnetoplasmon emission processes contribute and satellites only appear on the high bias side of the main resonance. The mechanism proposed here may be used to study the magnetotunneling in high-mobility systems where disorder is at minimum.
Response Function Of A Two-Dimensional Electron Gas In A Unidirectional Periodic Potential , S. M. Stewart, C. Zhang
Response Function Of A Two-Dimensional Electron Gas In A Unidirectional Periodic Potential , S. M. Stewart, C. Zhang
Chao Zhang
The dynamical density-response function of a periodically modulated two-dimensional electron gas under a perpendicular magnetic field is calculated within the random-phase approximation. It is found that the response function is not only broadened by the periodic potential, it also contains a series of subsingularities at the band edges. The maximum number of subsingularities is 2nmax, where nmax is the number of occupied Landau leveles (the last level may be partially filled). It is further proposed that light-scattering or electromagnetic absorption experiments can be performed to study these predicted structures.
Transport Of Spin-Polarized Electrons In A Magnetic Superlattice , J. Liu, W. Deng, K. Xia, C. Zhang, Z. Ma
Transport Of Spin-Polarized Electrons In A Magnetic Superlattice , J. Liu, W. Deng, K. Xia, C. Zhang, Z. Ma
Chao Zhang
We investigated the ballistic transport of two-dimensional electrons subjected to a periodically modulated magnetic field in the presence of the spin-orbit coupling of both the Rashba and the Dresselhaus types. It is shown that the spin splitting leads to additional gaps in the band structure and a series of minima in the transmission probability. The boundaries of the superlattice cause a finite spin polarization which can be tuned by the magnetic field, the electronic energy, and the superlattice period. The potential of such magnetic modulated structures as spin filters is discussed.
Effects Of Collective Excitations On The Quantum Well Intersubband Absorption, X. W. Mi, J. C. Cao, C. Zhang, F. B. Meng
Effects Of Collective Excitations On The Quantum Well Intersubband Absorption, X. W. Mi, J. C. Cao, C. Zhang, F. B. Meng
Chao Zhang
The dependence of the intersubband absorption spectra on the Coulomb interaction and quantum well (QW) width is studied. Rather than following the Fermi–Dirac distribution, we have solved the intersubband equations of motion to determine the subband population self-consistently. We have gone beyond the linear absorption theory to show the effect of various many-body interactions on the absorption spectra. It is found that the redistribution of electrons in excited states reduces the absorption. Our results indicate that the line shape and peak position are determined by the interplay of different collective excitations, such as the Fermi edge singularity and the intersubband …
Tunneling Spectroscopy Of Hole Plasmons In A Valence-Band Quantum Well , B. R. Neves, T. J. Foster, L. Eaves, P. C. Main, M. Henini, D. J. Fisher, M. L. Lerch, A. D. Martin, C. Zhang
Tunneling Spectroscopy Of Hole Plasmons In A Valence-Band Quantum Well , B. R. Neves, T. J. Foster, L. Eaves, P. C. Main, M. Henini, D. J. Fisher, M. L. Lerch, A. D. Martin, C. Zhang
Chao Zhang
We investigate the current-voltage characteristics of a p-doped resonant tunneling diode. In the voltage range slightly above the bias corresponding to resonant tunneling of holes into the first light-hole subband of the quantum well, we observe two satellite peaks which we attribute to plasmon-assisted tunneling transitions. A theoretical model is presented to account for these peaks. The model is based on the excitation of intrasubband and intersubband heavy-hole plasmons in the quantum well by hot holes injected close to the energy of the first light-hole subband. We also study the behavior of the satellites when a magnetic field is applied …
Nonlinear Response Formula For An Interacting Two-Dimensional Electron Gas Under A Magnetic Field And Microwave Radiation, T. Toyoda, M. Fujita, H. Koizumi, C. Zhang
Nonlinear Response Formula For An Interacting Two-Dimensional Electron Gas Under A Magnetic Field And Microwave Radiation, T. Toyoda, M. Fujita, H. Koizumi, C. Zhang
Chao Zhang
Introducing a canonical transformation of the second quantized field operators for two-dimensional interacting electrons under a uniform static magnetic field and a microwave radiation field, an exact formula that transforms the retarded density response function of the electrons to that of the electrons without the radiation field is derived. The formula provides a new way to treat the effects of the microwave radiation field on the electron density response when the conventional linear response approximation is not applicable.
Hartree-Fock Method Posed As A Density-Functional Theory: Application To The Be Atom, A. Holas, N. H. March, Y. Takahashi, C. Zhang
Hartree-Fock Method Posed As A Density-Functional Theory: Application To The Be Atom, A. Holas, N. H. March, Y. Takahashi, C. Zhang
Chao Zhang
The Hartree-Fock ground-state energy and electron density are first shown to be derivable from a local one-body effective potential v(r). As a nontrivial example, attention is then focused on the Be atom and isoelectronic atomic ions, the wave functions being written in terms of the density amplitude and phase. Some related general comments on the two-level one-dimensional system are included; kinetic-energy density is shown to be a local functional of electron density generated by the harmonic-oscillator potential.
Electron Correlations In A Double-Quantum-Well Structure, C. Zhang
Electron Correlations In A Double-Quantum-Well Structure, C. Zhang
Chao Zhang
The electron correlation effect in a double-quantum-well structure is investigated. The local-field correction and static structural factors are calculated for these structures. It is found that the static structural factors show an anomalous behavior at small q due to the coupled quantum-well-plasma excitation and the interlayer structural factor is negative at large q. We also found that the long-wavelength acoustic plasma mode is further softened due to short-range electron correlations. The minimum critical well separation for this mode to exist increases by an amount ∼1/kf1, where kf1 is the Fermi wave vector of the well with higher electron concentration.
The Effect Of The Electron Energy Spectrum On Electronic Efficiency And Power In Thermionic And Thermoelectric Devices, Mark F. O'Dwyer, T. E. Humphrey, R. A. Lewis, C. Zhang
The Effect Of The Electron Energy Spectrum On Electronic Efficiency And Power In Thermionic And Thermoelectric Devices, Mark F. O'Dwyer, T. E. Humphrey, R. A. Lewis, C. Zhang
Chao Zhang
We show that the details of the energy spectrum of transmitted electrons in thermionic and thermoelectric devices have a significant impact on their performance. We distinguish between traditional thermionic devices where electron momentum is filtered in the direction of transport only and a second type, in which the electron filtering occurs according to total electron momentum. Our main result is that the electronic efficiency of a device is not only improved by reducing the width of the transmission filter, but also strongly depends on whether the transmission probability rises sharply from zero to full transmission. Finally, we comment on the …
Plasmon Assisted Resonant Tunneling In A Double Barrier Heterostructure , C. Zhang, M. L. Lerch, A. D. Martin, Philip E. Simmonds, L. Eaves
Plasmon Assisted Resonant Tunneling In A Double Barrier Heterostructure , C. Zhang, M. L. Lerch, A. D. Martin, Philip E. Simmonds, L. Eaves
Chao Zhang
When a double barrier semiconductor structure is biased near a tunneling resonance, charge can accumulate in the quantum well. Coupling between this two dimensional electron gas and the tunneling current is investigated. Experimental data taken inside a region of apparent bistability in one device reveal a satellite on the high energy side of the current resonance in the I(V) characteristic. A theoretical model based on the many-body transfer Hamiltonian formalism shows that a plasmon excitation has remarkably similar structure. Magnetic field data support the plasmon satellite interpretation.
Magneto-Photon-Phonon Resonances In Two-Dimensional Semiconductor Systems Driven By Terahertz Electromagnetic Fields, W. Xu, C. Zhang
Magneto-Photon-Phonon Resonances In Two-Dimensional Semiconductor Systems Driven By Terahertz Electromagnetic Fields, W. Xu, C. Zhang
Chao Zhang
In this paper, we propose to study the magneto-photon-phonon resonance effects observed in terahertz (THz)-driven two-dimensional electron gases in strong magnetic fields. The photon energy of the THz electromagnetic radiations is on the scale of the cyclotron energy (induced by strong magnetic fields) and the LO-phonon energy so that (i) THz radiations will modify strongly the process of electron energy relaxation in the device structure; (ii) electrons can gain the energy from ac and dc driving fields through, e.g., absorption of the photons and lose the energy through, e.g., emission of the LO phonons; and (iii) resonant scattering will occur …
Thermionic Cooling Of Optoelectronic And Microelectronic Devices, S. P. Lee, B. C. Lough, R. A. Lewis, C. Zhang
Thermionic Cooling Of Optoelectronic And Microelectronic Devices, S. P. Lee, B. C. Lough, R. A. Lewis, C. Zhang
Chao Zhang
Solid-state thermionic cooling has gained attention recently because of its potential high cooling power. Thermionic devices based on semiconductor heterostructures utilize the band-edge offset at a heterojunction as the thermionic emission potential barrier and a thin layer to separate the cold and hot junction. In this paper, we present the behavior of thermionic coolers with periodic barriers using gallium arsenide/aluminium gallium arsenide (GaAs/Al/sub x/Ga/sub 1-x/As) semiconductor heterostructures. The exact numerical calculation to model the device performance has shown that the thermal efficiency in a multilayer structure is optimised when the effect of phonon scattering is introduced in the model. Besides, …
Terahertz-Driven Nonlinear Electrical Transport In Semiconductor Nanostructures, C. Zhang
Terahertz-Driven Nonlinear Electrical Transport In Semiconductor Nanostructures, C. Zhang
Chao Zhang
In this work, we used the quantum transport equation and density matrix formalism to calculate the frequency dependent electrical current of a two-dimensional electron gas directly driven by an intense terahertz laser. It is found that due to increased electron-photon coupling, the electron-impurity scattering decreases rapidly with the electric field.