Bidimensional Electron Gas Research Articles

Room-Temperature AlGaN/GaN Terahertz Plasmonic Detectors with a Zero-Bias Grating

In this paper, we present sensitivity measurement as well as measured and calculated absorption spectra for AlGaN/GaN THz plasmonic detector made of a metallic grating in-between two ohmic contacts. Detectors with different grating patterns have been fabricated and their sensitivity, reaching 1.9 μA/W at 77 K and 0.7 μA/W at 300 K, measured with a voltage applied between the ohmic contacts. It is the first time that such a detector shows THz detection with no voltage applied on the grating, namely with a bidimensional electron gas (2DEG) having a homogeneous electron density. These results are consistent with detection by drag-effect rectification. Measurements held between 0.648 and 0.690 THz show that the dependence of the sensitivity on the frequency follows the absorption spectrum, indicating that absorption is a crucial step in the detection process. Further simulations of absorption spectra show the tunability offered by such detector and allow us to predict frequency behavior for grating-biased detectors as well, in which the rectification is mainly governed by ratchet effect.

Contribution to the 1/f noise analysis in a bi-dimensional electron gas

The 1/f noise is investigated in an epitaxial AlGaAs/GaAs/AlGaAs heterostructure in the temperature range of [4–300 K]. The sample is biased at very low voltage to avoid velocity saturation at low temperature. Hooge parameters are determined at very low frequency assuming the absence of correlation between existing noise sources. These parameters are weakly fluctuating but do not show clear variation with temperature; αH varies in the range of 10−5 to 10−2, which are higher than theoretical values based on the mobility fluctuations. γ remains close to unity. αH and γ values suggest that the 1/f noise originates from the mobility fluctuation due to the lattice scattering, but the difference between theoretical and experimental αH suggests the existence of the noise originating from electron number fluctuations.

Intersubband polaritons in the electrical dipole gauge

We provide a theoretical description for the coupling between the intersubband excitations of a bi-dimensional electron gas with the electromagnetic field. This description, based on the electrical dipole gauge, applies to an arbitrary quantum heterostructure embedded in a general multilayered waveguide or a microcavity. We show that the dipole gauge Hamiltonian automatically takes into account the Coulomb interactions in this system. Furthermore, it can be conveniently expressed in terms of the many-body collective plasmon modes, which interact both with each other and with the light field. The dipole gauge therefore provides a suitable framework for the study of solid state Quantum Electrodynamics (QED) phenomena, such as the ultra-strong light-matter interaction regime, occurring at very high electronic densities.

An Effective Mass Theorem for the Bidimensional Electron Gas in a Strong Magnetic Field

We study the limiting behavior of a singularly perturbed Schrödinger-Poisson system describing a 3-dimensional electron gas strongly confined in the vicinity of a plane (x, y) and subject to a strong uniform magnetic field in the plane of the gas. The coupled effects of the confinement and of the magnetic field induce fast oscillations in time that need to be averaged out. We obtain at the limit a system of 2-dimensional Schrödinger equations in the plane (x, y), coupled through an effective selfconsistent electrical potential. In the direction perpendicular to the magnetic field, the electron mass is modified by the field, as the result of an averaging of the cyclotron motion. The main tools of the analysis are the adaptation of the second order long-time averaging theory of ODEs to our PDEs context, and the use of a Sobolev scale adapted to the confinement operator.

Photoluminescence study of the nitrogen content effect on GaAs/GaAs 1 − xN x/GaAs/AlGaAs: (Si) quantum well

We study the effect of nitrogen content in modulation-doped GaAs/GaAs 1 − x N x /GaAs/GaAlAs:(Si) quantum well using low-temperature photoluminescence spectroscopy. The samples were grown on GaAs (001) substrates by molecular-beam epitaxy with different nitrogen compositions. The variation of the nitrogen composition from 0.04% to 0.32% associated to the bi-dimensional electron gas gives a new interaction mode between the nitrogen localized states and the GaAs 1 − x N x /GaAs energies levels. The red-shift observed in photoluminescence spectra as function of nitrogen content has been interpreted in the frame of the band anticrossing model.

Adiabatic quantum-fluid transport models

Coupled quantum-fluid models are derived by means of a diffusion approximation from adiabatic quantum-kinetic models. These models describe the electron transport of a bidimensional electron gas. Particles are confined in one direction (denoted by $z$) while transport occurs in an orthogonal direction (denoted by $x$). The length-scale in the $z$ direction is comparable to the de Broglie wavelength, while the $x$-length scale is much bigger. The aim of this paper is to investigate the diffusion limit from quantum-kinetic to quantum-fluid models, which are numerically more interesting. Transitions between sub-bands are considered in the Fermi Golden rule setting.

An unusual nonlinearity in current-voltage curves of a bidimensional electron gas at low temperatures

Electrical characterization of a bidimensional electron gas transport has been investigated. Three AlGaAs∕GaAs heterostructures have been used for the study. Hall measurements have been performed at 4.2K and current-voltage characteristics at fixed temperatures between 4.2 and 300K. Measurements have been made using a four-point probe method. A saturation of the current at weak electric fields was observed in the range of low temperatures (<100K). The channel conductivity, the contact resistance, the electron mobility and the bidimensional electron gas density were determined. Electron drift velocities were deduced from current-voltage curves at the beginning of the saturation regime at 4.2K and compared with those found in the literature. The saturation, giving weak velocity, is related to impurity and alloy scatterings. Drift velocities close to the Fermi velocity are related to the Gunn effect. A Schottky effect has been observed at low temperatures (<100K) when the electron transport is perpendicular to the direction leading to the saturation of the current. This Schottky behavior indicates degradation of Ohmic contacts in the Au∕Ni∕Ge structure constituting the source and the drain.

Strong coupling between bi-dimensional electron gas and nitrogen localized states in heavily doped GaAs 1− xN x structures

We report a low-temperature photoluminescence spectra (LTPL) of GaAs 1− x N x layers and two-dimension electron gas (2DEG) GaAs 1− x N x /AlGaAs modulation doped heterostructure grown on GaAs substrates by molecular beam epitaxy (MBE) with low nitrogen content [N] = 2 × 10 18 cm −3. At low temperature, PL spectra of GaAs 1− x N x layers are governed by several features associate to the excitons bound to nitrogen complexes, these features disappear in (2DEG) GaAs 1− x N x /AlGaAs modulation doped heterostructure and the PL peak energy decrease with the laser power excitation. This effect is explained by the strongly coupling of the (2DEG) fundamental state with the nitrogen localized states. An activated energy of about 55 meV is deduced by photoluminescence measurements in the 10–300 K range for a laser power excitation P = 6 W/cm 2.

On a Vlasov–Schrödinger–Poisson Model

A Vlasov–Schrödinger–Poisson system is studied, modeling the transport and interactions of electrons in a bidimensional electron gas. The particles are assumed to have a wave behaviour in the confinement direction (z) and to behave like point particles in the directions parallel to the electron gas (x). For each fixed x and at each time t, the eigenfunctions and the eigenenergies of the Schrödinger operator in the z are computed. The occupation number of each eigenfunction is computed through the resolution of a Vlasov equation in the x direction, the force field being the gradient of the eigenenergy. The whole system is coupled to the Poisson equation for the electrostatic interaction. Existence of weak solutions is shown for boundary value problems in the stationary and time-dependent regimes.

Analysis of a Drift-Diffusion-Schrödinger–Poisson model

A Drift-Diffusion-Schrödinger–Poisson system is presented, which models the transport of a quasi bidimensional electron gas confined in a nanostructure. We prove the existence of a unique solution to this nonlinear system. The proof makes use of some a priori estimates due to the physical structure of the problem, and also involves the resolution of a quasistatic Schrödinger–Poisson system. To cite this article: N. Ben Abdallah et al., C. R. Acad. Sci. Paris, Ser. I 335 (2002) 1007–1012.

Photoreflectance measurements in GaAs/AlGaAs asymmetric quantum wells

In this work we investigated the optical control of the bidimensional electron gas density in a single asymmetric quantum well using, for the first time, photoreflectance. We performed our measurements at 80 and 300 K as a function of the power density of the pump beam. Under strong illumination, the bidimensional electron gas density is washed out of the quantum well and under a dark condition, it reaches its maximum value. The variation of the optical transitions observed in our photoreflectance spectra was related to the induced changes of the band profile in between these two limiting cases.

PARTICLE SIMULATION OF BIDIMENSIONAL ELECTRON TRANSPORT PARALLEL TO A HETEROJUNCTION INTERFACE

This paper is devoted to the numerical study, using the deterministic particle method, of the parallel transport of a bidimensional electron gas confined in a potential well near a heterojunction interface. The geometry makes it possible to solve independently the transport under the electric field and the well shape. We simulate the electronic transport with a kinetic model and use the deterministic particle method. As for the description of the potential well, we use different models and compare their influence on the thermodynamic equilibrium and on the transport properties of the electron gas.

Emission of [formula omitted] asymmetric modulation-doped multiple quantum wells under different excitation conditions by Kr + and Ar + lasers

We have studied the photoluminescence of a GaAs Al xGa 1−xAs asymmetric modulation doped multiple quantum well (AMDQW) structure. The spectra show an emission line at 1.526ev, when the sample is excited by Kr + laser, which corresponds to a transition in the wells. Under similar excitation conditions by Ar + laser two lines, coming from the wells, have been observed at 1.521ev and 1.545ev. In both cases these lines shift toward higher energies as the excitation intensity increases. From our results we conclude the lines at 1.521ev(1.526ev) and 1.545ev correspond to transitions due to recombination of the bidimensional electron gas (2DEG) confined in two different conduction sub-bands and that the mentioned shift represents a decrease in the 2DEG density.