Amorphous (a-)Ge films deposited on air-cleaved CaF2 (111) substrates were irradiated with 1,8 MeV Si ions, and the microstructure of the irradiated Ge films was examined by using Rutherford backscattering spectrometry combined with channeling technique, X-ray diffraction measurement and transmission electron microscopy. It was found that the ion irradiation can induce solid phase epitaxial growth (SPEG) of Ge (111) films even at low sample temperature (T-s) of approximately 200 degrees C, although the films included some randomly oriented crystals. In contrast to this, a-Ge films practically did not crystallize during heat treatment at 200 degrees C and the polycrystal films were only obtained when temperatures reached more than 500 degrees C. These results suggest that ion irradiation enhances the SPEG of a-Ge/CaF2 heterosystem at relatively low T-s values.