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 order to study the dynamics of photogenerated carriers and excitons in semiconductor superlattices by lime resolved photoinduced mid-infrared absorption. Using variable energies for both pump and probe, the measured photoinduced transients yielded the photoinduced absorption spectra at different excitation energies, the excitation spectra at different probe energies and both at varying delay times. We conclude from these measurements that a resonantly photogenerated excitonic population reaches thermal distribution within a few picoseconds of the excitation, much slower than photogenerated carriers with excess energy. We find that it takes roughly 0.1 ns for the photogenerated population to equilibrate with the lattice temperature, and that this time depends on the excess energy by which the photogenerated population in created. After thermal equilibrium with the lattice is reached, the excitonic population decays on a sub-nanosecond time scale which is linearly dependent on the lattice temperature.