Ion-bombardment-enhanced diffusion during the growth of sputtered superlattice thin films

A technique is presented for determining the enhancement in solid-state diffusion caused by low-energy ion bombardment. In this technique, superlattice films are grown under varying conditions of ion bombardment and the amplitude of the resulting composition modulation wave is determined by analyzing x-ray diffraction satellite peaks surrounding the central Bragg peaks. The amplitude is in turn related to the enhanced diffusion coefficient D* (x) which may be expressed as D*0 exp(−x/δ) where δ is a characteristic diffusion length of the ion-bombardment-produced defects. This approach was confirmed experimentally using InSb/GaSb superlattice structures grown by multitarget sputtering, each sample having equilayer thicknesses between 12 and 30 Å. D* was found to increase as the sputtering pressure was decreased. Measured values of D* averaged over the enhanced diffusion region were on the order of 10−17 cm2/sec compared to a thermal interdiffusion coefficient of approximately 10−22 cm2/sec at the film growth temperature of 250 °C.