Ion implantation damage and crystalline-amorphous transition in Ge

Experimental studies on the damage produced in (100) Ge substrates by implantation of Ge⁺ ions at different energies (from 25 to 600 keV), fluences (from 2×10¹³ to 4×10¹⁴ cm⁻²) and temperature (room temperature, RT, or liquid-nitrogen temperature, LN₂T) have been performed by using the Rutherford backscattering spectrometry technique. We demonstrated that the higher damage rate of Ge with respect to Si is due to both the high stopping power of germanium atoms and the low mobility of point defects within the collision cascades. The amorphization of Ge has been modeled by employing the critical damage energy density model in a large range of implantation energies and fluences both at RT and LN₂T. The experimental results for implantation at LN₂T were fitted using a critical damage energy density of ∼1 eV/atom. A fictitious value of ∼5 eV/atom was obtained for the samples implanted at RT, essentially because at RT the damage annihilation plays a non-negligible role against the crystalline–amorphous transition phase. The critical damage energy density model was found to stand also for other ions implanted in crystalline Ge (Ar⁺ and Ga⁺).