Reflection x-ray pole figure analysis techniques were used to study the heteroepitaxial relationships of the cobalt germanideCoGe2to GaAs(100). The alloy films were grown using the partially ionized beam deposition technique, in which low energyGe+ions are employed to alter the heteroepitaxial orientation of theCoGe2deposits. TheCoGe2[001](100)∥GaAs[100](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 eVGe+ions. Lowering the substrate temperature or reducing theGe+ion energy leads toCoGe2(100)orientation domination withCoGe2[100](010)∥GaAs[100](001)andCoGe2[100](001)∥GaAs[100](001).Substrate temperature alone was seen to produce only theCoGe2(100)orientation. ForCoGe2(001)films, additional energy was required fromGe+ions in the evaporant stream. ©1997 American Institute of Physics.