Monique Combescot

The dielectric constant and plasma frequency of p-type Ge like semiconductors

Abstract The interband transitions in the valence band effect noticeably the Drude-Zener usual formula for the dielectric constant and the plasma frequency in the case of a p-type Ge-like semiconductor. The trapping of holes in acceptor sites is discussed and limits the observability of this effect.

Bose-Einstein Condensation in Semiconductors: The Key Role of Dark Excitons

Bose-Einstein condensation in semiconductors is controlled by the nonelementary-boson nature of excitons. Pauli exclusion between the fermionic components of composite excitons produces dramatic exchange couplings between bright and dark states. In microcavities, where bright excitons and photons form polaritons, they force the condensate to be linearly polarized, as observed. In bulk, they also force linear polarization, but of dark states, due to interband Coulomb scatterings. To evidence this dark condensate, indirect processes are thus needed.

Electron-hole plasma generation and evolution in semiconductors

Abstract We discuss various physical problems related to dense electron-hole (e-h) plasmas in silicon-like semiconductors such as: the e-h plasma energy in the quantum and classical limits including the actual band structure; the dielectric constant using the appropriate plasma frequency mass and the variation of the plasma relaxation time due to e-h collisions; the plasma generation including its nonlinear aspect when the e-h density passes the plasma frequency density of the pump beam; the e-h plasma evolution due to Auger recombination and impact ionization as well as the e-h plasma hydrodynamics; finally, we will discuss also the possibility of a very fascinating melting at T =0.

Influence of the electron-hole density profile on the reflectivity of laser irradiated silicon

Abstract We study the influence of the spatial extension of the electron-hole plasma created by a pump pulse on the reflectivity of a probe pulse. We show that the density deduced from reflectivity measurements is the surface density value with a very good accuracy, except very close to the plasma resonance. We also show that the resonance broadening due to the spatial inhomogeneity can be larger than the one due to free carriers absorption and has to be included in the usual experimental determination of the plasma relaxation time.

Polarisation effects for the excitonic stark shift at all detunings

Abstract We show that a laser beam in the transparency region of a direct-gap semiconductor splits the exciton line into five or three shifted lines depending on the degeneracy of the upper valence band. We give the polarisations of the pump and probe beams necessary to observe these shifted lines. We confirm that at large detuning, the excitonic shifts are simply the blue shifts obtained for independent electrons, i.e. (2 + 4) or (2 + 2)-levels atoms, while at small detuning, compared with the exciton binding energy, the shifts are modified by the Coulomb interaction. In particular, one exciton line red shifts, at the two-photon absorption threshold, when the molecular biexciton is stable.

Trion ground state, excited states, and absorption spectrum using electron-exciton basis

We solve the Schr{o}dinger equation for two electrons plus one hole by writing it in the electron-exciton basis. The main advantage of this basis is to eliminate the exciton contribution from the trion energy in a natural way. The interacting electron-exciton system is treated using the recently developed composite boson many-body formalism which allows an exact handling of electron exchange. We numerically solve the resulting electron-exciton Schr{o}dinger equation, with the exciton levels restricted to the lowest

SCATTERING PROCESSES IN SEMICONDUCTORS

1s, 2s

Current relaxation processes in highly excited semiconductors

and

Direct Auger recombination in degenerate direct gap semiconductors

3s

Screening of the Electron-Phonon Interaction in Semiconductors

states, and we derive the trion ground state energy as a function of the electron-to-hole mass ratio. While our results are in reasonable agreement with those obtained through the best variational methods using free carrier basis, this electron-exciton basis is mostly suitable to easily reach the bound and unbound trion excited states. Through their wave functions, we here calculate the optical absorption spectrum in the presence of hot carriers for 2D quantum wells. We find large peaks located at the exciton levels, which are attributed to electron-exciton (unbound) scattering states, and small peaks identified with trion bound states.