Gennanium (Ge) is a group-IV indirect band gap semiconductor but the difference between its direct and indirect band gap is only 140 me V. It has been shown that when Ge is subjected to a tensile strain and a heavy n-doping level, room-temperature photoluminescence (PL) can be greatly enhanced. Among these two factors, achieving a heavy n-doping level in Ge (i.e., electron concentrations higher than 1 x 10 exponent 19 cm-3) is a challenge since the solubility of most group-V elements (P, As, Sb) in Ge is very low. The authors report here Ge growth on silicon substrates using molecular beam epitaxial (MBE) technique. To enhance the n-doping level in Ge, a specific n-doping process based on the decomposition of the GaP compound has been implemented. The GaP decomposition allows producing P2 molecules, which have a higher sticking coefficient than that of P4 molecules. the authors show that phosphorus doping at low substrate temperatures followed by flash thermal annealing are essential to get a high doping level. the authors have obtained an activate phosphorus concentration up to 2 x 10 exponent 19 cm-3 and room-temperature PL measurements reveal an intensity enhancement up to 50 times. This result opens a new route for the realization of group-IV semiconductor optoelectronic devices.