Abstract: A Ge 0.976 Sn 0.024 n +/p diode was formed using phosphorus ion P + implant and rapid thermal annealing at 400 °C. Activation of P in Ge typically requires high temperatures (e.g., 700 °C), and it was found that this is not needed in the presence of a small amount of Sn. A high forward bias current of 320 A/cm 2 at-1 V is achieved for the Ge 0.976 Sn 0.024n +/diode. This is four times higher than that of the Ge n +/p control diode, which received the same P + implant but activated at 700 °C. The n +-GeSn region has a high active dopant concentration of 2.1 × \10 19cm -3, much higher than that in the Ge control. The increased active dopant concentration in GeSn reduces the width of the tunneling barrier between the Al contact and the n +-GeSn and increases the forward bias diode current. Enhancement of P activation in Ge 0.976 Sn 0.024 could possibly be as a result of passivation of vacancies in the Ge lattice due to Sn atoms. © 2012 IEEE.