Intersubband transitions in semiconductor quantum wells are inspected with light in meV range. For low densities electron-phonon interaction dominates the relaxation processes. We theoretically inspect relaxation processes visible in 2D photon echo experiments.
Two-dimensional photon echo spectroscopy allows one to track relaxation and correlation processes in optically excited nanostructures. We analyze such spectra for intersubband transitions in an n-doped GaAs/Al0.35Ga0.65As single quantum well. Focusing on electron-longitudinal optical phonon interaction in a non-Markovian treatment, the carrier dynamics in the conduction subbands are investigated in the low density regime. Our results provide detailed information about the temporal evolution of electron-phonon correlations in the two-dimensional frequency spectrum.
A fully microscopic quantum theory for the photoluminescence of a semiconductor quantum well is summarized. The dynamic equations for the interacting electron–hole pairs (excitons), phonons and photons are presented and specialized for the situations of interacting electron–hole populations and low density excitonic populations. Signatures of phonon assisted exciton formation are discussed in the low density limit, where the early dynamics is found to be strongly dependent on the emission angle. For long times the decay can be described by an angle-independent decay rate.
The phonon scattering assisted luminescence of semiconductor quantum well excitons after short pulse excitation is investigated. The presented analysis is based on the low-density limit of a set of equations for quantum correlation functions for electrons, phonons, and photons. The dynamics of the correlation functions describes the optical excitation and the decay of the coherent exciton polarization as well as the generation of an incoherent exciton occupation and its luminescence decay. Numerical solutions of the equations of motion demonstrate strong competition effects of the exciton-phonon and the exciton-photon interaction on a picosecond time scale and lead to a nonmonotonous temperature dependence of the time-resolved spontaneous emission. The angle resolved emission resembles the generation and decay dynamics of the exciton density for different in-plane momenta.
Mechanisms for reduced interband absorption using intersubband coherence or intersubband coupling in semiconductor quantum wells are analyzed by exactly solving the density matrix equation. By placing some mild limitations on the diagonal density matrix elements, general analytic solutions are obtained without weak-field restrictions. Our solutions demonstrate reduced absorption, various nonlinear processes, and coupling-field-modulation of interband transitions. Our results agree well with previous results for three-level atomic systems, give insights into nonlinear mechanisms, and point out the importance of nonperturbative approaches to this class of problems.>
We report photon echoes from two-dimensional (2D) excitons in a GaAs-AlGaAs quantum well structure at 2 K. We analyze our data with a theoretical model of the generation of photon echoes by pulses of finite length which includes phase relaxation during excitation. A line shape analysis yields the phase relaxation time of 2D excitons. We find that the phase coherence near the line center decays, together with the resonant population, within 4 ps, whereas well below line center the phase coherence is conserved for times up to 20 ps.