INTERSUBBAND DYNAMICS BELOW THE OPTICAL PHONON ENERGY FOR SINGLE AND COUPLED-QUANTUM-WELL SYSTEMS

We have made direct measurements of the intersubband lifetime in singl e GaAs quantum wells below the optical phonon energy at 36 meV, At low temperatures and excitations LO phonon emission is inhibited and acou stic phonon emission dominates; a sharp cross-over exists between the two regimes. Rate equation calculations have been performed for the si ngle well samples with no fitting parameters and these agree well with experiment. The calculations have been extended to coupled quantum we lls and we find that by careful tuning of the well widths the LO phono n rate can be tuned by up to an order of magnitude.