A.N. Borges

Polarizability of a donor impurity in a GaAsAlGaAs quantum wire

Abstract The polarizability and the ground state binding energy of a donor impurity located in a semiconductor quantum well wire of rectangular cross-section with finite barrier potential is calculated through the variational method. We assume that the donor is located at the center of the wire and that the electric field is applied in the direction perpendicular to the wire length ( z -direction), making an angle θ with the x -axis. We present our results for the ground state binding energy as a function of the size of the wire for several values of the electric field strength and of the angle θ. It is found that the polarizabilities decrease as the wire dimensions ( L x and L y ) decrease, until they reach a minimum at a certain value of L x ( L y fixed) and then increase as the width becomes smaller. The binding energies and the polarizabilities, as expected, have a strong dependence on the geometrical form of the wire and on the angle θ.

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.

Cyclotron mass of electrons in GaN-Al xGa1-xN heterostructures

The quasi-two-dimensional electron cyclotron mass in GaN-AlxGa1- xN heterostructures is theoretically calculated. The shifting in Landau Levels due to the electron Longitudinal Optical phonon interaction is calculated through the Second Order Improved Wigner Brillouin Perturbation Theory (IWBPT). Experimental results recently obtained for GaN heterojunction are well described by the theory. We have also investigated the e ects of the electronic density on the Cyclotron Resonance frequency.

'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.

Quasi-one-dimensional polaron gas in a GaAs quantum wire

In this work we present a study of the plasmon-longitudinal-optical (LO) phonon collective excitation as a function of the quasi-one-dimensional wave vector for several electronic densities and thickness of the wires. We observed that the intra- and intersubband excitation collective energies are very sensitive to electronic density variation. This effect is more pronounced for the lower branch of the collective excitation energy and for narrower wires. Our calculations are performed using the Singwi, Tosi, Land and Sjolander (STLS) theory, at zero temperature, assuming a three-subband model, where only the first subband is occupied by electrons.

Magnetopolaron effects on the donor states in InP

In this work, we investigate the magnetopolaron effects on the transition energies between the intradonor levels 1s-2p± placed in InP bulk semiconductor. In spite of the InP Frolich electron-longitudinal optical phonon coupling constant (α=0.12) be greater than the GaAs (α=0.07), we employ in the calculation the same theoretical tools successfully applied for GaAs structures, a mix between variational method and perturbation theory. A good agreement between our theoretical results and the available experimental results were observed mainly in the region below the resonance, for magnetic field B≤25T.

Magnetopolaron effects on the intradonor 1s-2p+ transition energies in a GaAs - AlGaAs double quantum well

In this work we present a calculation of the intradonor 1s-2p+ transition energies for an impurity donor present in a GaAs-AlGaAs Double Quantum Well structure as a function of an applied external magnetic field. In our calculation the impurity energy levels were obtained from a variational method by choosing a Gaussian trial wave function, and the energy corrections due to the polaronic effect were included by second order perturbation theory IWBPT as modified by Cohn, Larsen and Lax. We have considered only the GaAs bulk LO phonon in the electron-phonon coupling. A very good agreement between the theoretical and experimental results for a DQW consisting of two 100 A well widths separated by a 100 A potential barrier width was obtained.