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

Abstract

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.