Growth and characterization of short-period silicon isotope superlattices

We report molecular beam epitaxy (MBE) growth of silicon isotope superlattices (SLs) composed of alternating layers of isotopically enriched ²⁸Si and ³⁰Si. In this work, we have prepared short-period ²⁸Si_n/³⁰Si_n isotope SLs, where n is the number of atomic monolayer, with n = 1, 2, 3, 4, and 7. Zone-folded optical phonon frequencies due to artificial mass periodicity in the growth direction have been observed by Raman spectroscopy. We have used planar bond-charge model to calculate the frequencies. We found that the frequencies of the observed Raman shift agree well with those of optical phonon modes calculated for each SL structure. A detailed analysis revealed that the degree of intermixing between adjacent layers for our condition is approximately two monolayers.