Damage formation in Ge during Ar+ and He+ implantation at 15 K

摘要

Ar+ and He+ ions were implanted into Ge samples with (100), (110), (111) and (112) orientations at 15 K with fluences ranging from 1 x 10(11) to 1 x 10(14) cm(-2) for the Ar+ ions and fluences ranging from 1 x 10(12) to 6 x 10(15) cm(-2) for the He+ ions. The Rutherford backscattering (RBS) technique in the channelling orientation was used to study the damage built-up in situ. Implantation and RBS measurements were performed without changing the target temperature. The samples were mounted on a four axis goniometer cooled by a close cycle He cryostat. The implantations were performed with the surface being tilt 7 degrees off the ion beam direction to prevent channelling effects. After each 300 keV Ar+ and 40 keV He+ implantation, RBS analysis was performed with 1.4 MeV He+ ions. For both the implantation ions, there is about no difference between the values found for the damage efficiency per ion for the four different orientations. This together with the high value (around 5 times higher than that found in Si), gives rise to the assumption of amorphous pocket formation per incident ion, i.e. direct impact amorphization, already at low implantation fluences. At higher fluences, when collision cascades overlap, there is a growth of the already amorphized regions.