GROWTH AND ELLIPSOMETRIC STUDIES OF PERIODIC AND CANTOR APERIODIC AMORPHOUS GE SI SUPERLATTICES/

Artificial superlattices of amorphous germanium (a-Ge) and amorphous s ilicon (a-Si) were deposited using dual-target magnetron d.c. sputteri ng on Si(001) substrates. The superlattices were fabricated with modul ations according to deterministic aperiodic sequences as well as perio dic sequences. The deterministic aperiodic sequences were made accordi ng to the generation of generalized Cantor sets. Optical characterizat ion of the superlattices were carried out with spectroscopic ellipsome try. The optical properties of the Cantor and periodic superlattices w ith equal a-Ge:a-Si volume ratios were compared. We found that the int erference peaks from the Cantor superlattices are more pronounced comp ared with the interference peaks from the periodic superlattices. The periodic superlattices could be modelled with both multilayer and effe ctive-medium models, in contrast to the Cantor superlattices for which only multilayer models were appropriate. This is, to our knowledge, t he first study of Cantor superlattices.