F. Comas

Polar optical oscillations of layered semiconductor structures in the long-wavelength limit

Polar optical oscillations coupled to unretarted electric fields are discussed for the long-wavelength limit with application to layered semiconductor structures (quantum wells, superlattice, etc.). A Lagrangian formalism is adopted for the deduction of the equations of both mechanical and electrical quantities. The obtained equations bear the form of second-order coupled differential equations for the fundamental quantities, displacement field u and electric potential г. Matching boundry conditions are rigorously derived from the equations and interpreted physically. The particular case of materials belonging to the cubic symmetry is discussed with special application to the double heterostructure. Some comments are also made about the case of isotropic constituent materials. We have thus settled a theory for long- wavelength oscillations taking into account dispersion up to quadratic terms in the wave vector (through the introduction of medium internal stresses) with the aim of avoiding some problems which have been detected and discussed in earlier treatments of this subject.

Polaron effective mass and binding energy in a semiconductor heterostructure

Abstract Polaronic corrections are calculated for a parabolic weak coupling polaron in a single heterostructure. A modified electron-LO-phonon Hamiltonian is applied considering that LO-vibrations from one side of the heterostructure do not penetrate into the other side. The zero temperature case is assumed and screening is included along the lines of the Thomas-Fermi approach. The exact wave functions (Airy functions) are utilized for confining the potential of the triangular form including an infinite barrier at the interface. Comparison with earlier works on the subject is made.

Magnetopolaron in a quantum well: LO-phonon confinement effects

Abstract Magnetopolarons in a polar-crystal slab are studied considering electron coupling with confined LO-phonons. The electron self-energy is calculated by use of a standard perturbation theory treatment. It is demonstrated that phonon confinement lowers polaron effects. The influence of electron coupling to interface phonons on the polaron shift is discussed. Special attention is paid to the magnetophonon resonance. Phonon dispersion is shown to be important for the interpretation of the pinning of the transition frequencies in high magnetic fields to values much lower than the Brillouin zone center longitudinal optical phonon frequency.

LO-phonon confinement effects on the polaron properties in semiconductor quantum-well heterostructures

Abstract Polaronic corrections are calculated for a semiconductor quantum-well heterostructure at T = 0 K. Electron coupling with confined LO-phonons is assumed on the basis of an electron-LO-phonon model Hamiltonian deduced in a previous work. Screening is ignored during the calculations, a parabolic band structure is supposed and the case of completely confined electrons with infinite potential barriers at the interfaces is considered. Finite values for the electron self-energies are obtained. Dependence of polaronic corrections on the quantum-well parameters is discussed in detail and comparison with other works on the subject is made. Good agreement with experimental data is found for the case of a GaAs-Al x Ga 1− x As quantum well.

Low temperature mobility in SiSi1−xGex quantum wells

We present electron mobility calculations for an SiSi1−xGex quantum well for conduction along the Si channel at low temperatures. The Boltzmann transport equation is applied in the relaxation time approximation and two scattering mechanisms are discussed: by impurities and by acoustic phonons (via deformation potential coupling). Giving the latter mechanism its due weight proved to be essential in order to achieve good agreement with the experimental results.

Piezoelectric-phonon scattering in the transport properties of low-dimensional semiconductor heterostructures

Abstract Relaxation times of quasi-one-dimensional (Q1D) and quasi-two-dimensional (Q2D) semiconductor heterostructures are calculated for the case of piezoelectric-phonon scattering. The case of acoustic-phonon scattering is also considered for the sake of comparison. The limits Q1D→Q2D and Q2D→3D are analysed. Ohmic and Hall mobilities are calculated in the so-called size-quantum-limit (when only the first sub-band is populated and inter-sub-band transitions are neglected). Low-temperature asymptotic formulae for the mobilities are deduced in each case. The special case of the GaAs/AlGaAs heterostructures is discussed and the conclusion is drawn that acoustic-phonon mechanism is dominant in the low-temperature regime when other scattering mechanisms (mainly ion-impurity scattering) can be neglected. Comparison with earlier results is made, some inaccuracies of previous works are eliminated and the role of piezoelectric-phonon mechanism is clearly established. Calculations are done in the low carrier concentration case neglecting screening and using non-degenerate carrier statistics.

Non-equilibrium distribution function in polar direct gap semiconductors

Abstract Electron distribution function (EDF) for non-equilibrium configurations in polar direct gap semiconductors is obtained in the temperature range k B T ⪡ ħ ω Lo . The sample is assumed to be free of impurities and crystal defects. Electron-phonon coupling is the main relaxation mechanism. Master equation is solved approximately and analitycal expressions for EDF are obtained. Average electron energy as a function of temperature is discussed.

Hot Electron Power Losses in a Quantum Well: A Realistic Polar Optical Phonon Model

Calculations of hot electron power losses in a semiconductor quantum well are reported on the basis of a realistic phenomenological model for polar optical phonons and the corresponding Frohlich-type electron-phonon Hamiltonian. This model has been discussed in recent times and leads to a plausible description of such phonons. Hot electrons are taken in a steady state configuration when the temperature model is applicable. We assume a wide range of relatively low electron temperatures (25 to 100 K) and the contribution of acoustic phonons is also included. Comparison with previous theoretical and experimental work is made with the fundamental aim of evaluating the relative importance of this model for polar optical phonons for the description of power losses in a quantum well.