Monolayer (ML) thick Ge deposition on (100) Si substrates by molecular beam epitaxy (MBE) technique using an ultrathin SiO2 interlayer has been studied by ion beam analysis and photoluminescence (PL). The dependence of the Ge layer growth mode on the amount of the deposited Ge and the SiO2 thickness has been investigated. Atomic hydrogen treatment has been performed in order to passivate non-radiative recombination channels and to enhance the PL intensity. We conclude the formation of Ge quantum dots for the sample with the thickest Ge and SiO2 layers (9 angstrom and 1 ML, respectively).