Highly P doped Ge layers are proposed as a material to realize an on-chip laser for optical interconnect applications. In this work, we demonstrate that these donor impurities have a dramatic impact on the excess carrier lifetime and introduce detrimental many-body effects such as linewidth broadening in the gain medium. Linewidth broadening Γopt = 10 meV for undoped Ge and Γopt ≥ 45 meV for Ge with a doping level up to 5.4 × 1019 cm−3 were extracted using photoluminescence spectroscopy and pump-probe spectroscopy. In addition, we observed that the excess carrier lifetime (τc) drops by more than an order of magnitude from 3 ns in undoped Ge to <0.3 ns in doped Ge.

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