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Epitaxial in situ doped Si0.73Ge0.27 alloys were grown selectively on patterned bulk Ge and bulk Si wafers. Si0.73Ge0.27 layers with a surface roughness of less than 3 nm were demonstrated. Selectively grown p+Si0.73Ge0.27 layers exhibited a resistivity of 3.5 m&Omega, cm at a dopant concentration of 2.5 &times, 1019 boron atoms/cm3. P+/n diodes were fabricated by selectively growing p+- Si0.73Ge0.27 on n-doped bulk Ge and n-doped Si wafers, respectively. The geometrical leakage current contribution shifts from the perimeter to the bulk as the diode sizes increase. Extracted near midgap activation energies are similar to p+/n Ge junctions formed by ion implantation. This indicates that the reverse leakage current in p+/n Ge diodes fabricated with various doping methods, could originate from the same trap-assisted mechanism. Working p+/n diodes on Ge bulk substrates displayed a reverse current density as low as 2.2&middot, 10&minus, 2 A/cm2 which was found to be comparable to other literature data. The layers developed in this work can be used as an alternative method to form p+/n junctions on Ge substrates, showing comparable junction leakage results to ion implantation approaches.