Depths of Low-Energy Ion Bombardment Damage in Germanium

Abstract

The depth of the damage induced in thin films (≈10 μ) of germanium by bombardment with low‐energy (≤1000 eV) argon ions has been measured by a new technique. The method is based on the differences in sputtering yield for a given energy, between material previously damaged by a higher‐energy bombardment and material previously undamaged. The change in yield when the previously damaged material is eroded away marks the depth of this region. The sputtering yield was obtained from changes in the resonant frequency of a piezoelectric quartz crystal on which the thin germanium films were deposited and annealed. The detector was sensitive to mass changes of 4×10⁻¹⁰ g/cm². The depth of the damaged region was found to be eight atomic layers when the damaging ions were of 400‐eV energy increasing up to 25 atomic layers for damage induced by 1‐keV argon ions. The extent of the damage induced by 1‐keV argon ions was measured as a function of damaging ion dosage and found to saturate at doses of 1×10¹⁷ ions/cm² and greater. Analysis indicates the damage could be accounted for in part by embedded argon atoms. The depth of the damage was found also to depend on the film thickness in the case of very thin films. Effects of annealing treatments during film deposition are described.