Phonon-assisted modulation of the electron collection efficiency into InxGa1-xAs/GaAs quantum wells

he energy relaxation and the capture of free carriers in InxGa1-xAs/GaAs quantum wells have been investigated by means of continuous-wave and time-resolved photoluminescence for excitation energies tuned over a wide interval above the GaAs band-gap. The strong interaction between free electrons and longitudinal-optical phonons gives rise to a 42 meV-period modulation of the efficiency of carrier collection into the well and of the corresponding collection time. The energy position of the electronic level driving the capture into the well has been deduced from the data and does not coincide with any calculated energy level of the well structure. The capture time turns out to be at the limit of our time resolution (approximate to 20 ps), while the collection time oscillates with an amplitude of about 80 ps, because of the emission of acoustic phonons.