Marcos H. Degani

Interaction of optical phonons with electrons in GaAs quantum wires

Abstract The energy and the effective mass of an electron in a quantum-well wire of GaAs surrounded by Ga 1− x Al x As is calculated in the presence of electron-LO-phonon interaction using a variational approach. The polaron mass is found to be dramatically dependent on the sizes of the wire, and also that its magnitude is greater than that in comparable two- and three-dimensional semiconductor structures.

Stark ladders in strongly coupled GaAs‐AlAs superlattices

The energy spectrum of a superlattice in the presence of an electric field is calculated using the split time scheme. It is shown that even for a low field two interpenetrating Stark ladders exist in a GaAs‐AlAs superlattice and the spacing between the energy levels in each of the ladders is eEd. When the external field is increased the number of ladders with the same period eEd is also increased.

Electron-interface-phonon interaction in GaAs/AlAs and InAs/GaSb heterojunctions

Abstract We report for the first time a theory which treats the polaronic effects in quasi-two-dimensional semiconductor structures by taking into account the interaction of the electron with the surface, interface and bulk phonon modes. The results obtained show that the dominant electron-phonon interaction involves the interface phonon modes for the case of thin layers.

Many-polaron interaction effects in GaAs-GaAlAs quantum-well-wires

Abstract We calculate the electron-phonon contribution to the ground-state energy of a quasi- one-dimensional gas of interacting polarons by using the self-consistent-field approximation theory proposed by Singwi, Tosi, Land and Sjolander for the response function of the electron system. The present results are applied to GaAs-GaAlAs quantum-well-wires with the appropriate form factors that take into account the influence of the finite width of the electron layer. The Hartree-Fock and RPA results are also presented for comparison. We have found that screening effects on the electron-electron and electron-phonon interactions are more effective in quantum wires of small sizes. We also notice that correlation and exchange effects are more evident in wires of reduced dimensions.

Electron-phonon effects on the ground impurity level in quasi-one-dimensional semiconductor heterostructures

Abstract We calculate the effects of the electron-phonon interaction on the binding energies of an impurity placed in a quantum-well wire of rectangular cross section and finite barrier potential to the confined electrons. The calculations are performed as a function of the size of the wire for different positions of the impurity and for several values of the heights of the barrier potential. The results show that the energies are almost the same in wires with comparable cross-sectional area.

Competition between interface and bulk phonons in GaAs/AlAs and InAs/GaSb quantum wells

Abstract We present some new theoretical results on the coupling between an electron and the interface and bulk phonons in semiconductor quantum wells. The results show that the dominant contribution to the energy and effective mass comes from the interface modes in the case of thin layers.

Cyclotron resonance of electrons in GaAsGa1−xAlxAs heterojunctions

Abstract The cyclotron resonance mass of a quasi-two-dimensional polaron in GaAsGaA1As heterostructures and quantum wells is calculated. Experimental results recently obtained by different groups are well described in the magnetic quantum limit.

Temperature dependence of the polaron mass in a GaAsGa1−xAlxAs quantum well wire

Abstract We discuss the interaction of quasi-one-dimensionally confined electrons in GaAsGaAlAs heterojunctions with polar optical phonons. The free energy of this system is obtained by using Feynmans path-integral formalism. Numerical results are presented for the effective mass and self energy of this polaron as a function of temperature, for different values of the size of the quantum-well wire.

Two dimensional electrons trapped on a helium surface

A simply unitary-transformation formalism is used in order to investigate the ground-state properties of an electron bounded on a liquid-helium surface and interacting with the surface modes of oscillation (ripplons). A first-order phase-transition-like behavior from the quasifree to the self-trapping electron state as the clamping external electric field exceeds a certain critical value is observed. The results are presented for both cases, electrons on films of helium adsorbed on solid neon and electrons at the interface of phase separated 3He-4He mixtures.

SUBSTITUTIONAL DONOR RELATED STATES AND AU/GE/NI CONTACTS TO ALXGA1-XAS

Abstract Current-voltage measurements performed on bulk AlxGa1−xAs equipped with Au/Ge/Ni contacts reveal surprising deviations from ohmic behaviour when the temperature is lowered to that of liquid nitrogen. Significant differences are observed between samples with x = 0.3 (direct band-gap material) and x = 0.5 (indirect band-gap material). The dominant states of the donor atoms Si (doping) or Ge are found to be responsible for such behaviour. Evidence for the existence of an effective-mass X-valley metastable state is also presented.