Low-temperature molecular beam epitaxy of Ge on Si

Multilayers of Ge were deposited on (0 0 1) Si at low temperatures (250 and 300∘C). The structural characterization was done by X-ray diffraction and reflectivity as well as by atomic force microscopy technics. The photoluminescence (PL) spectra reveal a quantum well (QW) emission that shifts to lower energy with increasing Ge thickness. Besides this shift, we observe a change in the energy of the TO phonon from that of the Si-Si to that of the Si-Ge vibration. Passivation measurements enable us to separate the QW luminescence from the defect-related emission.