Obtaining heavily-doped n-type germanium (Ge) is difficult since n-type dopant activation in Ge is limited to less than 5× 1019 cm -3 which is far below the solid solubility limit of phosphorus (P) in Ge. Such poor activation has limited the rectifying properties of n +/p Ge diodes. This work is aimed at understanding the challenge of forming highly rectifying n+ /p diode as well as enhancing rectification of n+ /p diode by using antimony (Sb) and P coimplantation process. Enhanced n+ doping of greater than 10 20 cm-3 in Ge obtained by Sb/P codoping results in enhanced rectification in Ge n+ /p junction diode. © 2011 American Institute of Physics.