Two-Dimensional Triplet Magnetoexcitons and a Magnetofermionic Condensate in the GaAs/AlGaAs Heterostructures

A fundamentally new collective state, namely, the magnetofermionic condensate, is discovered during photoexcitation of a sufficiently dense gas of long-lived triplet cyclotron magnetoexcitons in a twodimensional Hall insulator with a high electron mobility, a filling factor of ν = 2, and temperatures of T < 1 K. The condensed phase coherently interacts with an external electromagnetic field, exhibits superradiant properties in the recombination of correlated condensate electrons with heavy holes in the valence band, and spreads nondissipatively in the layer of a two-dimensional electron gas to macroscopical large distances, transferring an integer spin. The observed effects are explained in terms of a coherent condensate in a nonequilibrium system of two-dimensional fermions with a fully quantized energy spectrum, in which a degenerate ensemble of long-lived triplet magnetoexcitons obeying the Bose statistics is present.

     

Temperature Dependence of Polaron Cyclotron Resonance Mass in GaAs/AlGaAs Heterostructures

The temperature dependence of polaron cyclotron resonance mass in GaAs/AlGaAs heterostructures is reinvestigated theoretically. By taking into account the electron-longitudinal-optic phonon interaction with temperature-dependent many-body effects, the conduction band non-parabolicity, and the influence of nonzero magnetic field, a good agreement with experiment is obtained.     

Capture of carriers excited by interband and intersubband absorption in GaAs/AlAs/AlGaAs double-barrier quantum wells

We report on the carrier dynamics in n-type double-barrier quantum well structures in an electric field. Both the intersubband and interband photocurrents, excited by long-wavelength (4μm) and short-wavelength (0.5μm) radiation, respectively, show a photovoltaic asymmetry with respect to the applied field. This asymmetry arises from an internal field due to an asymmetric dopant distribution with respect to the well centers. Time-dependent photoluminescence measurements allow us to determine the field dependence of the electron and hole capture times.     

Effect of Phonon Focusing on the Thermal Conductivity of GaAs/AlGaAs Heterostructures at Low Temperatures

Physics of the Solid State - The effect of the anisotropy of elastic properties on the thermal conductivity of GaAs/AlGaAs heterostructures at low temperatures is investigated. The effect of phonon...     

A theoretical study on the electronic structure of GaAs/AlAs and AlAs/GaAs core/shell nanoparticles

Results of theoretical investigation on the structural and electronic properties of GaAs/AlAs and AlAs/GaAs core/shell nanoparticles are presented. We have considered relaxed structures of essentially spherical parts of the zinc-blende crystal structure. The electronic properties and the total energy were calculated using density-functional tight-binding method. Our results include the charge distribution, density of states (DOSs), electronic energy levels (in particular HOMO and LUMO), HOMO-LUMO gap, excitation spectra and their variation with shell thickness for both GaAs/AlAs and AlAs/GaAs core/shell systems.     

Effects of Weak Localization and Electron–Electron Interaction in GaAs–AlGaAs Heterostructures

The influence of the processes of weak localization and electron–electron interaction in an inhomogeneous two-dimensional electron gas of a single GaAs–AlGaAs heterojunction on the low-temperature transport characteristics in the case of occupation of two quantum subbands has been investigated. The transport characteristics have been interpreted from the viewpoint of a two-layer model taking into account the existence of two bypass conduction channels corresponding to the two-dimensional and three-dimensional electron gas. Both the electrical and optical measurements point to the existence of large-scale fluctuations of the potential, which determine the dependence of the conduction and the Hall resistance of the heterostructures on the magnetic field. It has been established that the weak localization determines the charge transport in a weak magnetic field, and the electron–electron interaction determines this transport in a strong magnetic field.     

Influence of thin AlAs layer insertion on intersubband optical transitions in GaAs/AlGaAs quantum- well structures

In this work, we demonstrate the thin AlAs layer insertion into GaAs/AlGaAs quantum well (QW) structures and its influence in energy transition in the frequency range of mid-infrared. To realize the more accurate calculation, the graded interface model of QW structures is integrated into our self-consistent solving of Schrodinger and Poisson equations to obtain the energy level and envelope wave functions of QW. We find the thin AlAs layer inserted at various positions in the well can obviously tune intersubband optical transitions. The corresponding tuning range can be 50 meV. We find that the thicker AlAs layer (2 monolayers) can provide wider tuning range and larger oscillator strength between subbands 1 and 3, compared with the thinner one (1 monolayer). Our results suggest that thin semiconductor layer may be an idea optimization design for the quantum well terahertz lasers which are based on optical pumping with mid-infrared lasers.     

GaAs/AlAs super-flat interfaces in GaAs/AlAs and GaAs/(GaAs) (AlAs) quantum wells grown on (4 1 1)A GaAs substrates by MBE

Effectively atomically flat GaAs/AlAs interfaces over a macroscopic area (“super-flat interfaces”) have been realized in GaAs/AlAs and GaAs/(GaAs) (AlAs) quantum wells (QWs) grown on (4 1 1)A GaAs substrates by molecular beam epitaxy (MBE). A single and very sharp photoluminescence (PL) peak was observed at 4.2 K from each GaAs/AlAs or GaAs/(GaAs) (AlAs) QW grown on (4 1 1)A GaAs substrate. The full-width at half-maximum (FWHM) of a PL peak for GaAs/AlAs QW with a well width ( ) of 4.2 nm was 4.7 meV and that for GaAs/(GaAs) (AlAs) QW with a smaller well width of 2.8 nm (3.9 nm) was 7.6 meV (4.6 meV), which are as narrow as that for an individual splitted peak for conventional GaAs/AlAs QWs grown on (1 0 0) GaAs substrates with growth interruption. Furthermore, only one sharp peak was observed for each GaAs/(GaAs) (AlAs) QW on the (4 1 1)A GaAs substrate over the whole area of the wafer (7 7 mm ), in contrast with two- or three-splitted peaks reported for each GaAs/AlAs QW grown on the (1 0 0) GaAs substrate with growth interruption. These results indicate that GaAs/AlAs super-flat interfaces have been realized in GaAs/AlAs and GaAs/(GaAs) (AlAs) QWs grown on the (4 1 1)A GaAs substrates.     

AlGaAs/InGaAs/GaAs赝配高电子迁移晶体管的kink效应研究

利用二维器件模拟软件MEDICI对AlGaAs/InGaAs/GaAs赝配高电子迁移晶体管器(PHEMT)件进行了仿真，研究了PHEMT器件的掺杂浓度与电子浓度分布，PHEMT器件内部的电流走向及传输特性，重点研究了不同温度和不同势垒层浓度情况下PHEMT器件的kink效应.研究结果表明：kink效应主要与处于高层深能级中的陷阱俘获/反俘获过程有关，而不是只与碰撞电离有关. 关键词： 高电子迁移率晶体管 kink效应 二维电子气     

Transport Studies on GaAs/AlGaAs Two-Dimensional Electron Systems Modulated by Triangular Array of Antidots

Triangular antidot lattices of various periods and aspect ratios are fabricated on high mobility GaAs/AlGaAs two-dimensional electron systems(2DESs),and are characterized by magneto-transport measurements at low temperatures down to 300 mK. Commensurability peaks are generally observed in the magneto-resistivity ρ_(xx),and remarkable similarity between dρ_(xy)/dB and ρ_(xx) is found. In samples of relatively large aspect ratio d/a, the Aharonov-Bohm-type oscillations are clearly observed in both ρ_(xx) and ρ_(xy), as well as the quenching of the Hall resistivity ρ_(xy) in the vicinity of B = 0. These observations evince the good quality of our samples, and attest to the adequate preparation for fabricating antidot lattices of a reduced period to realize artificial graphene from GaAs/AlGaAs 2DESs.     

Delocalization of phonon-plasmon modes in GaAs/AlAs superlattices with tunnel-thin AlAs barriers

The technique of Raman spectroscopy has been used to investigate doped (n-type) and undoped GaAs/AlAs superlattices with AlAs barrier thicknesses from 17 to 1 monolayers. The peak corresponding to the scattering by a two-dimensional plasmon was found in the Raman spectrum of a doped superlattice with relatively thick barriers. The position of the experimental peak corresponded to the value calculated in the model of plasma oscillations in periodic planes of a two-dimensional electron gas. The electron tunneling effects played an increasingly prominent role as the AlAs barrier thickness decreased. The peaks corresponding to the scattering by coupled phonons with three-dimensional plasmons were found in the Raman spectra for a superlattice with an AlAs thickness of 2 monolayers; i.e., the delocalization of coupled modes was observed. In this case, the folding of acoustic phonons was observed in the superlattice under consideration, indicative of its good periodicity, while the localization of optical phonons in GaAs layers was observed in undoped superlattices with an AlAs thickness of 2 monolayers.     

Study of defects in proton irradiated GaAs/AlGaAs solar cells

The properties of GaAs/AlGaAs solar cells irradiated with 40, 70, 100 and 170 keV protons have been studied. Current-voltage (IV) measurement showed that the worst degradation was found in the cells irradiated by 100 keV protons. The degradation was found defect dependent. Defect profile was obtained by the stopping and range of ions in matter (SRIM) simulation and deep-level transient spectroscopy (DLTS) measurement. In order to obtain the deep-level defect profile in depletion layer by DLTS measurement, the traditional calculation formula of defect concentration has been modified. DLTS measurement showed good agreement with that of the SRIM simulation.     

Scattering of electrons in the GaAs/AlAs transistor structure

This paper reports on the results of a self-consistent calculation of the rates of electron scattering from surface roughnesses, acoustic phonons, and polar optical phonons in a transistor structure based on a GaAs quantum wire in an AlAs matrix at temperatures T = 77 and 300 K. The rates of electron scattering are calculated in the electric-quantum limit approximation with due regard for both the collisional broadening of the electron energy spectrum and the Pauli principle. The influence of the gate voltage on these rates is investigated. The wave function of electrons and the energy level of their quantum ground state are determined by the self-consistent solution of the Poisson and Schrödinger equations.     

Polarization of hot photoluminescence in GaAs/AlAs superlattices

The polarization characteristics of hot photoluminescence in GaAs/AlAs superlattices are investigated experimentally and theoretically. It is shown that the formation of an electronic miniband in the superlattice substantially changes the polarization characteristics of the photoluminescence. As a result of the quasi-three-dimensional character of the motion of hot electrons in the superlattice, the polarization depends on the ratio of the electron kinetic energies in the plane of the superlattice and along the axis of the superlattice. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 4, 285–289 (25 February 1996)     

Suppressed intermixing in InAlGaAs/ AlGaAs/GaAs and AlGaAs/GaAs quantum well heterostructures irradiated with a KrF excimer laser

The influence of gallium arsenide surface modification induced by irradiation with a KrF excimer laser on the magnitude of the quantum well (QW) intermixing effect has been investigated in InAlGaAs/AlGaAs/GaAs QW heterostructures. The irradiation in an air environment with laser pulses of fluences between 60 and 100 mJ/cm² has resulted in the formation of a gallium oxide-rich film at the surface. Following the annealing at 900 °C, up to 35 nm suppression of the band gap blue shift was observed in all the laser irradiated samples when compared to the non-irradiated samples. The origin of suppression has been discussed in terms of stress controlled diffusion. PACS 78.55.Et; 66.30.Lw; 73.21.Fg