Energy relaxation during hot-exciton transport in quantum wells: Direct observation by spatially resolved phonon-sideband spectroscopy

Abstract

We investigate the energy relaxation of excitons during the real-space transport in ZnSe quantum wells by using microphotoluminescence with spatial resolution enhanced by a solid immersion lens. The spatial evolution of the LO-phonon sideband, originating from the LO-phonon assisted recombination of hot excitons, is measured directly. By calculating the LO-phonon assisted recombination probability, we obtain the nonthermal energy distribution of excitons and observe directly the energy relaxation of hot excitons during their transport. We find the excitons remain hot during their transport on a length scale of several micrometers. Thus, the excitonic transport on this scale cannot be described by classical diffusion.

Theoretical analysis of higher-order phonon sidebands in semiconductor luminescence spectra

“…When the electron-phonon interaction is sufficiently strong, these resonances can be observed as replica of the excitonic peak that are commonly referred to as phonon sidebands while the exciton peak is called zero-phonon line in this context [1][2][3][4][5][6][7]. Recent experiments have demonstrated that the sideband intensities can be of the same order of magnitude or even larger than the intensity of the zero-phonon line.…”

Quasi-ballistic transport of excitons in quantum wells

“…Various regimes of non-classical exciton transport can be studied in ZnSe-based quantum wells (QWs) using continuous-wave or time-resolved nano-PL [5,[7][8][9][10]. Right after the exciton generation one finds the regime of coherent, quasiballistic transport.…”

Ultrafast Breathinglike Oscillation in the Exciton Density of ZnSe Quantum Wells

“…However, the ultralong wavelength makes it hard to achieve high spatial resolution. It was shown that phonon-sideband (PSB) emission reflects the whole exciton population [12,16,17]. Indeed the spot diameter of this emission shows a clear oscillation within the first 30 ps for nonresonant excitation with arbitrary excess energy (see Fig.…”

“…E PL corresponds to the energy position of the maximum of the photoluminescence and in the present study n 2. Thus, by tuning the laser energy, we can directly vary the initial kinetic energy E kin of the excitons [12,13,16].…”