Mott transition of excitons in ZnSe studied by phase resolved reflection

Abstract

The Mott transition of excitons in a semiconductor with increasing carrier density is in principle well understood as a consequence of screening of the Coulomb interaction between carriers. While the position of the exciton stays widely unchanged the exciton peak disappears due to band gap shrinkage. However, a more quantitative check of applied theoretical models for the screening and of the role of quantum kinetic effects in this process is still open.We demonstrate that the phase‐resolved reflection in shallow‐confined ZnSSe heterostructures opens the possibility of a detailed study of the Mott transition due to the appearance of pronounced interferences effects of propagating polariton modes.Our theoretical approach for the investigation of the influence of excited carriers on the dielectric susceptibility is based (i) on a quasi‐particle approximation for the carrier energies and damping, and (ii) on the semiconductor Bloch equations including dynamical screening and a quantum kinetic treatment of scattering. These manybody effects lead to drastic changes of both amplitude and phase of the reflected light: Jumps of the phase are steepened, show abrupt changes from +π to –π and are smoothed out, and interference peaks in the amplitude decrease and disappear completely with increasing excitation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Mott transition of excitons in GaAs-GaAlAs quantum wells

“…However, the excitation in the experiments was rather low with densities of excited carriers well below the Mott transition. In [29,30], we extended our theoretical concept to higher excitations and to the description of the Mott transition in bulk ZnSe. The main point here was to include the renormalization of the dynamically screened carrier self-energies and the chemical potentials within quasi-particle approximation (QPA) in a self-consistent way into the semiconductor Bloch equations, e.g.…”