Gas release studies of silicon implanted with low energy He+and Kr+ions

A silicon (111) surface was bombarded in U.H.V. with low energy (≤1 keV) He+ and Kr+ ions. The ions retained within the solid were subsequently desorbed into a closed volume, by raising the target temperature linearly, with respect to time, at a rate of 30°KS−1. The differentiated signal in a mass spectrometer provided desorption spectra. Two main release stages were noted, at ∼400°K and ∼1000°K. It is suggested that the former is related to divacancy motion, modified by the presence of gas and the latter to the annealing of bombardment-induced amorphousness. Helium was injected into a target which had been amorphized by prebombardment with krypton ions. The helium was largely released in the ∼400 °K stage and it was deduced that helium diffused through an amorphous layer at temperatures well below those required to anneal the amorphousness.