D. N. Mirlin

Optical alignment of 2D-electron momenta in multiple quantum well structures

Abstract A linear polarization of the recombination luminescence of photoexcited hot electrons in a multiple quantum well structure has been observed. The peculiarity of electron 2D-motion manifests itself in an observed increase of the polarization with 2D-motion energy. The time of optical-phonon emission by a 2D electron is determined by measuring a magnetic depolarization of the luminescence.

Dispersion of plasmon-phonon modes in semiconductors: Raman scattering and infrared spectra

Abstract In n-InP and n-GaAs the Raman scattering spectra from plasmon-phonon modes (PPM) with wave vector q ⋍ 10 6 cm -1 have been measured. The frequencies of PPM thus obtained are different from plasmon-phonon frequencies at q ⋍ 10 3 cm -1 evaluated from infrared reflectivity spectra. This difference is explained in terms of the spatial dispersion of PPM. Good agreement between observed and calculated frequencies is obtained. Additional broadening in Raman scattering spectra due to Landau damping has been observed. The observed shift of the bands in Raman spectra with different polarization of the scattered light relative to each other has been explained by taking into account the frequency dependence of the phonon contribution into the scattering, cross-section.

Magnetic field enhancement of Raman scattering on folded acoustic phonons in GaAs-AlGaAs superlattice

Abstract Drastic enhancement of the Raman scattering intensity of the folded longitudinal acoustic phonon in a GaAs/AlGaAs superlattice is observed in the presence of a perpendicular magnetic field. A qualitative quasi-classical interpretation of this phenomenon is presented and a dependence of Raman scattering intensity on the magnetic field is obtained.

Scattering of hot electrons by neutral acceptors in GaAs/AlAs quantum well structures

The optical alignment of hot electrons and its destruction in a magnetic field under conditions when electron scattering by neutral acceptors plays a large role is investigated. This makes it possible to determine the probability of the scattering of hot electrons from an initial photoexcited state, as well as the times characterizing the energy and momentum relaxation of hot electrons on scattering by neutral acceptors. The experimental results are compared with calculations.

The exciton photoluminescence and vertical transport of photoinduced carriers in CdSe/CdMgSe superlattices

The photoluminescence and photoluminescence excitation spectra, phonon-related Raman scattering, and vertical transport of photoinduced carriers and excitons along the growth direction in type I lowstrained CdSe/CdMgSe superlattices, which are grown on InAs substrates using molecular-beam epitaxy, are studied for the first time. The studies are carried out at various temperatures and excitation intensities. The vertical transport is studied by a purely optical method involving an enlarged quantum well built in into the superlattice. This well serves as a sink for the excitons and charge carriers tunneled through the superlattice. At 2–150 K, the carriers are preferentially transported by free excitons. However, in superlattices with periods of 5.9 and 7.3 nm, this transport is not of the Bloch type. A comparison of the calculated energies of the band-to-band transitions in the superlattices with the experimental data yields the relative magnitude of the valence-band offset in the range 0.4–0.5. The Raman spectra indicate that the behavior of optical phonons in CdMgSe is bimodal.

Inelastic scattering of hot electrons by neutral donors in heavily silicon-doped GaAs/AlAs quantum wells

The energy and momentum relaxation of hot electrons in n-type GaAs/AlAs quantum wells is studied. Hot photoluminescence due to the recombination of hot electrons with holes bound on Si acceptors is observed in structures with a high level of doping with silicon. Using the method of magnetic depolarization of hot photoluminescence, the probability of scattering of hot electrons is found to decrease substantially with increasing temperature in the range 4–80 K. This effect is shown to be due to the ionization of donors. It is established that the probability of inelastic scattering by neutral donors is several times greater than the probability of quasielastic electron-electron scattering.

Vertical transport of hot electrons in GaAs/AlAs superlattices

Ballistic transport of hot photoexcited electrons injected from a superlattice into an enlarged quantum well is studied using the polarized hot photoluminescence technique. It is established that most photoexcited electrons thermalize before they are captured by the enlarged QW; however, a minor fraction of them reach the enlarged quantum well ballistically, keeping their momentum-distribution anisotropy or spin orientation arising due to the absorption of linearly or circularly polarized light in the superlattice.

Magnetic-field-induced transitions between minibands in GaAs/AlxGa1−x As superlattices

The transition from closed to open electron orbits in a magnetic field has been studied by polarized hot electron photoluminescence (HEPL) in superlattices with varied widths of electron minibands. The dependence of the HEPL depolarization on the miniband width is observed. The strong depolarization occurring when the kinetic energy of electrons exceeds the energy gap between the minibands is interpreted in terms of a magnetic-field-induced transition between the electron minibands (magnetic breakdown).

Inelastic scattering of hot electrons in n-GaAs/AlAs types I and II multiple quantum wells doped with silicon

We have studied the dependence of hot electron scattering rate on temperature in n-GaAs/AlAs types I and II multiple quantum wells. For a sample with well width 37A, which is on the borderline between types I and II band alignment, the increase of the temperature in the range 6–80K leads to the strong decrease of the hot electron scattering rate. We explain this result by ionization of donors and transfer of cold electrons from the Γ-valley of GaAs to the X-valley of AlAs.

Dimensionality effects in the hot-electron photoluminescence of gallium arsenide: 2D-quasi-3D transition

The influence of the miniband width in superlattices on the polarization characteristics of hot-electron photoluminescence (HEPL) is investigated. It is shown that the energy dependence and the magnetic field dependence of polarization change significantly as the width of the electron minibands increases. The limits of applicability are established for the tight-binding approximation in the calculation of optical transitions in superlattices.