Microstructure of germanium films crystallized by high energy ion irradiation

Amorphous (a-)Ge films deposited on air-cleaved CaF 2 (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°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°C and the polycrystal films were only obtained when temperatures reached more than 500°C. These results suggest that ion irradiation enhances the SPEG of a-Ge/CaF 2 heterosystem at relatively low T s values.