TIME-RESOLVED PHOTOINDUCED INTERSUBBAND ABSORPTION - A NOVEL AND POWERFUL WAY OF STUDYING THE DYNAMICS OF QUANTUM STRUCTURE CARRIERS

A novel interband-pump intersubband-probe technique is developed in or der to study the dynamics of photogenerated carriers and excitons in s emiconductor superlattices by lime resolved photoinduced mid-infrared absorption. Using variable energies for both pump and probe, the measu red photoinduced transients yielded the photoinduced absorption spectr a at different excitation energies, the excitation spectra at differen t probe energies and both at varying delay times. We conclude from the se measurements that a resonantly photogenerated excitonic population reaches thermal distribution within a few picoseconds of the excitatio n, much slower than photogenerated carriers with excess energy. We fin d that it takes roughly 0.1 ns for the photogenerated population to eq uilibrate with the lattice temperature, and that this time depends on the excess energy by which the photogenerated population in created. A fter thermal equilibrium with the lattice is reached, the excitonic po pulation decays on a sub-nanosecond time scale which is linearly depen dent on the lattice temperature.