Reflection x-ray pole figure analysis techniques were used to study the heteroepitaxial relationships of the cobalt germanide CoGe2 to GaAs(100). The alloy films were grown using the partially ionized beam deposition technique, in which low energy Ge+ ions are employed to alter the heteroepitaxial orientation of the CoGe2 deposits. The CoGe2(100)||GaAs(001) orientation, which has the smallest lattice mismatch, was found to occur for depositions performed at a substrate temperature around 280 °C and with ∼1200 eV Ge+ ions. Lowering the substrate temperature or reducing the Ge+ ion energy leads to CoGe2(100) orientation domination with CoGe2(010)||GaAs(001) and CoGe2(001)||GaAs(001). Substrate temperature alone was seen to produce only the CoGe2(100) orientation. For CoGe2(001) films, additional energy was required from Ge+ ions in the evaporant stream. © 1997 American Institute of Physics.