Paulo César Miranda Machado

The effects of magnetic field on the energy levels of shallow donor impurities in GaAs/AlxGa1-x as quantum dots

Abstract In the present work, we report a calculation of the electron energy levels (1s,2p−,2p+) and the binding energies of a shallow impurity placed in the center of a circular quantum dot of a GaAs surrounded by AlGaAs in the presence of a uniform magnetic field applied perpendicularly to the plane of the dot. We also present results for the 1s−2p+ transition energy as a function of the magnetic field.

The effects of the plasmon-LO phonon interaction on the critical densities of RPA approach in a quasi-one-dimensional system

In this work we have studied the electron LO phonon interaction on the pair-correlation function g(x) and its dependence on the electronic density for a GaAs-AlGaAs rectangular quantum wire within the random-phase approximation (RPA). We assumed two different values of the wire width. As negative non-physical results are found for lower electronic densities and small interparticle separations in the RPA approach, we have delimited the regions where the RPA approach cannot be used for the calculation of the Q1D electron gas collective excitation.

Plasmon–LO phonon interaction effects on the intrasubband and intersubband transition energies in a quantum well wire

Abstract The electron–longitudinal optical phonon coupling effects on the collective excitations energy spectra of quasi-one-dimensional electrons confined in a GaAs–AlGaAs rectangular quantum well wire are investigated. The calculation of the energies is performed within the random phase approximation using a three-subband model. It was verified that the polaronic coupling is a very important effect and cannot be neglected in the calculation of the plasmon collective excitation.

Polaronic effects on the collective excitation energies in a quantum wire

In this work we report a investigation of the plasmon-longitudinal-optical (LO) phonon interaction effects on the intersubband and intrasubband collective excitation energies in a GaAs-AlνGa1-νAs rectangular quantum well wire. We observe a resonant split of the collective excitation energy into two branches, one with energy lower and other with energy higher than the LO-optical phonon energy ℏωLO. Our calculations are performed using a self-consistent field approximation, which includes the local-field correction within the Singwi, Tosi, Land, and Sjolander (STLS) theory at zero temperature and assuming a three-subband model, where only the first subband is occupied by electrons. The potential confining effects on the collective energies were also considered.

Potential Barrier Height Effects on the Intrasubband and Intersubband Quasi-One-Dimensional Plasmons

The effects of the potential barrier height on the collective excitations of a electron gas confined in a GaAs-AlxGa1-xAs quantum wire of rectangular cross-section are investigated theoretically. For several potential barrier heights, we calculated the plasmon energy, structure factor and pair-correlation function, within the Random-Phase Approximation regime, considering a three-subband model with only the lowest subband populated by electrons. We verified that the intersubband plasmon is more sensitive to the potential barrier height variation than the intrasubband plasmon. We also observed that the confining potential effect decreases with the increasing of the wire-width.

SHORT-RANGE CORRELATION EFFECTS IN A POLARON GAS IN GaAs AlGaAs QUANTUM WELL WIRES

We investigate the short-range correlation effects of plasmon–phonon collective excitations in a quantum well wire by using the self-consistent field approximation theory proposed by Singwi, Tosi, Land and Sjolander [Phys. Rev.176, 589 (1968)]. In our calculation model, we consider a three-subband model with only one populated, for a rectangular cross-section quantum well wire with infinite height for the potential barrier. We have verified that by decreasing the wire width (and/or decreasing the electronic density), the local field correction effects are increased. We compare the present results with those obtained within the Random Phase Approximation throughout the paper and found that the differences between the two calculation methods are more significant for the intrasubband plasmon.

Further investigation on Frobenius Spectrum for DOA estimation

The SEAD method relies on the Differential Spectrum to provide accurate DOA estimation even at very low values of SNR. However, calculating the Differential Spectrum requires performing successive SVD for each test angle in a scanning range. Recently, we proposed using the Frobenius norm instead of the SVD to reduce the computational effort of the SEAD method. However, the resulting DOA estimation performance remained inferior to that using the SVD. In order to improve de robustness of the Frobenius Spectrum, this paper analyzes the components of the Frobenius norm aiming to realize advantages and disadvantages of using it. Then, a comparison of the resulting method to other SEAD based methods and MODEX has shown that Frobenius Spectrum is more sensitive for close angles, however, it has shown to be more robust for distant angles.

Polaronic effects on the collective excitation in a GaAs parabolic quantum wire

In this paper, the plasmon-longitudinal optical (LO) phonon interaction effects on the intrasubband structure factor, on the pair correlation function and on the intrasubband plasmon energy associated with the lowest subband in a GaAs parabolic quantum well wire (QWW) are investigated by varying the subband separation energy and the electronic density. The calculations are performed using the self-consistent field approximation, which includes the local-field correction within the Singwi, Tosi, Land and Sjolander (STLS) theory, at zero temperature and assuming a three-subband model where only the first subband is occupied by electrons. The theoretical results obtained via STLS theory are compared with the random phase approximation (RPA) approach results, in order to emphasize the importance of the local field corrections (LFC) for the calculation of the collective excitations in quasi-one-dimensional systems.

'Atomistic' simulation of ultra-submicron MESFETs

The effects of a discrete random dopant distribution on the MESFET characteristics were investigated using device simulation. The first three moments of the Boltzmann equation coupled to the Poisson equation are solved self-consistently. The model accounts for hot-electron effects, degeneracy and surface-states effects. The simulation indicates a nonuniform potential distribution in the active layer, which creates sharp variations in the electron density in that layer. It was also found that the drain electric current depends on the actual distribution of impurities. A comparison is made between the solutions of the transport equations for both dopant models (discrete and uniform) for MESFETs.

Inter-subband structure factor for a quasi-one-dimensional polaron gas

In this work, the collective excitation spectra of quasi-one-dimensional plasmon in a rectangular GaAs quantum wire is investigated. Our calculations are performed within the Singwi, Tosi, Land and Sjolander (STLS) self-consistent theory taking into account the plasmon–longitudinal optical (LO) phonon coupling effects. We have employed a three subband model with only the first subband occupied by electrons and we have considered intra-subband and inter-subband transitions. We show that the polaronic effects cause the appearance of dips and oscillations in the static structure factor dispersion relation, which are directly related with the oscillator strength transfer between the collective excitation energy branches. We have also observed oscillations in the pair-correlation function that are characteristic of inter-subband transitions and it denotes partial localization of the particle.