Institution: | a INFM, Dipartimento di Matematica e Fisica, Universita' di Camerino, Via Madonna della Carceri, 62032 Camerino (MC), Italy b INFM, Dipartimento di Fisica, Universita' di Roma “Tor Vergata”, 00133 Roma, Italy c INFM, Dipartimento di Scienze della Terra e dei Materiali, Universita' di Ancona, 60131 Ancona, Italy |
Abstract: | Si–Ge heterostructures made of 6 monolayers of Si and 4 monolayers of Ge repeated p times (Si6Ge4)p, strained on Si (1 0 0) substrates, have been investigated by photoluminescence measurements and electron microscopy. The films were grown at 400°C by molecular beam epitaxy, using Sb as surfactant. The photoluminescence results of the whole set of samples show similar spectra, for both the single Ge quantum well (p=1) and the thicker heterostructure (p=30). The phonon assisted transverse optical line is measured at about 40 meV far from the no-phonon one, and this corresponds to the Ge–Ge vibration. Our results demonstrate that excitonic recombination occurs mainly in the Ge layers and it is indirect in nature, whatever the repetition number (p) is. Furthermore, we evidenced a high localization of the photoluminescence process excluding any superperiodicity effect. |