Room-temperature photoluminescence intensity from Germanium (Ge) quantum dots (QDs) is highly enhanced by the Phosphorous (P) delta-doping at Ge QDs/Si interfaces since stronger confinements of electrons at the interfaces can be realized by the doping. Suppression of surface segregation of the doped P atoms, which is essential for the delta-doping with a sharp profile, is realized by the control of growth temperatures of Ge QDs and spacer-Si layers after P doping. It is, therefore, concluded that higher efficiency light emitting devices can be realized based on Ge QDs with optimal n-type doping and growth conditions. (C) 2017 Elsevier B.V. All rights reserved.