The impact of the growth temperature on the in-situ phosphorus doped Ge layer grown by chemical vapor deposition is studied to achieve a sufficiently high n-type carrier concentration for the realization of the quasi-direct band gap material in Ge. The use of a high order precursor gas, namely Ge2H6, allows to reduce the growth temperature down to 320 degrees C without degrading the material quality in view of optical applications. An active phosphorus concentration as high as 6.2 x 10(19)/cm(3) has been measured by Hall effect measurements. The achieved active phosphorus concentration is the highest among the reported concentrations for uniformly in-situ doped Ge layers. The high and almost fully (87%) activated phosphorus concentration results in a strong photoluminescence peak at room temperature, which intensity is 8.3 times higher compared to the photoluminescence intensity as measured for an undoped Ge layer. (C) 2015 Elsevier B.V. All rights reserved.