High-resolution photoluminescence measurement of the isotopic-mass dependence of the lattice parameter of silicon

We have studied the dependence of the lattice parameter of silicon on isotopic mass, using high-resolution photoluminescence spectroscopy to detect splittings of the shallow donor bound exciton transitions in epitaxial layers of either isotopically enriched Si28 or Si30 grown on silicon substrates of natural isotopic composition. The slight lattice parameter mismatch between the isotopically enriched epitaxial layer and the natural silicon substrate induces a biaxial strain in the epitaxial layer, which results in a splitting of the hole states in the bound exciton. This can be detected with remarkable precision, especially in the highly enriched Si28 epilayers, where the bound exciton lines are extremely sharp.