Abstract

Coulomb correlations are crucial for the realistic computation of semiconductor optical spectra.¹ In low-dimensional systems, band structure and quantum confinement effects play also a major role and have to be integrated in the theory. In our approach, the excited semiconductor is described by nonequilibrium Green’s functions for the interacting quasi-particles: carriers, photons, and plas-mons, whose time evolution is governed by Dyson Equations. Coupled band structure and quantum confinement effects are included in the carrier propagators, and in the transition matrix elements, which give rise to optical selection rules, and e.g., TE/TM mode discrimination. They are determined after diagonaliza-tion of the Luttinger Hamiltonian. The emission and absorption spectra are computed from the transverse polarization function, P, i.e., the self-energy that appears in the photon Dyson equation. Both P and the carrier selfenergy ∑, can be written as a sum of an RPA term and a Coulomb-correlation contribution, expressed by means of a T-matrix, which satisfies the Bethe-Salpeter equation. Figure 1 shows that for temperatures as low as 77 K, the inclusion of beyond-RPA corrections in ∑ does not affect the computed spectra. All other curves are thus computed within this approximation. Figure 2 shows absorption spectra of a 50-A GaAs/AlGaAs QW, as well as corresponding luminescence spectra. Notably, to the best of our knowledge for the first time, we predict a structure corresponding to a heavy-hole in the TM spectra. It arises due to a combination of T-matrix (Coulomb) and bandcoupling effects, i.e., it can not be described by simple free-carrier or many-body approaches without valence band coupling.

© 1998 Optical Society of America