Highly n-doped, tensile-strained Ge is grown on Si substrate with a three-step method by solid source molecular beam epitaxy. Tensile strain of 0.22% is obtained in the Ge film due to the thermal expansion mismatch between Si and Ge. Activated n-type doping concentration of 5.0x1018 cm(-3) is also realized by Sb in-situ doping during epitaxy and post-growth annealing. Strong photoluminescence (PL) is observed around 1.5-1.6 mu m from direct band gap transition of Ge at room-temperature. Starting from this material, free-standing microdisks are fabricated by electron beam lithography, dry etching of Ge and subsequent Si undercutting. Significantly enhanced light emission and sharp resonant peaks with Q-factor approaching 800, are observed in the PL spectra. (C) 2013 Elsevier B. V. All rights reserved.