Study of Ion-Bombardment Damage on a Ge (111) Surface by Low-Energy Electron Diffraction

An atomically clean and highly ordered Ge (111) surface was bombarded with Ar+ ions and the bombardment effects were studied by low-energy electron diffraction. Degradation characteristics of the (10) beam were most extensively investigated over an ion energy range from 10 eV to 1 keV with ion dosage ranging from 1012 to 1016 ions/cm2. The degradation characteristics determine the mean area of damage per incident ion. This area is 7×10−14 cm2 for a 1-keV Ar+ ion and 1×10−15 cm2 for a 40-eV ion. At low ion energies, some retention of (10) intensity is noted even for large dosages, indicating in this case that some short-range order is retained. The minimum ion energy for damage is ∼20 eV. This value is close to the sputtering threshold energy and the reported displacement energy of Ge. A bombardment damage model is proposed to explain the low-energy ion-bombardment characteristics. Thermal recovery of the bombarded surface shows a dependence on ion energy and also on total bombardment dose.