Accession Number:

ADA433758

Title:

Time-Resolved Electronic Relaxation Processes in Self-Organized Quantum Dots

Descriptive Note:

Final rept. 10 Jul 2000-31 Dec 2003

Corporate Author:

MICHIGAN UNIV ANN ARBOR CENTER FOR ULTRAFAST OPTICAL SCIENCE

Personal Author(s):

Report Date:

2005-05-16

Pagination or Media Count:

34.0

Abstract:

The authors have performed a comprehensive set of experiments on the dynamics of electrons and holes in semiconductor quantum dots, and a complete picture of the dynamics as a function of carrier density and temperature has emerged. Specifically, they have used two- and three-pulse femtosecond differential transmission spectroscopy to study the dependence of quantum dot carrier dynamics on temperature. At low temperatures and densities, the rates for relaxation between the quantum dot confined states and for capture from the barrier region into the various dot levels could be directly determined. For electron-hole pairs generated directly in the quantum dot excited state, relaxation is dominated by electron-hole scattering, and occurs on a 5-ps time scale. Capture times from the barrier into the quantum dot are on the order of 2 ps into the excited state and 10 ps into the ground state. The phonon bottleneck was clearly observed in low-density capture experiments, and the conditions for its observation namely, the suppression of electron-hole scattering for non-geminately captured electrons were determined. As temperature increases beyond about 100 K, the dynamics become dominated by the reemission of carriers from the lower dot levels due to the large density of states in the wetting layer and barrier region. Measurements of the gain dynamics show fast 130-fs gain recovery due to intradot carrier-carrier scattering, and picosecond-scale capture. Direct measurement of the transparency density versus temperature shows the dramatic effect of carrier reemission for the quantum dots to thermally activated scattering. The carrier dynamics at elevated temperatures are thus strongly dominated by the high density of the high-energy continuum states relative to the dot-confined levels. Deleterious hot carrier effects can be suppressed in quantum dot lasers by resonant tunneling injection.

Subject Categories:

  • Quantum Theory and Relativity
  • Solid State Physics
  • Thermodynamics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE