Interdiffusion in a symmetrically strained Ge/Si superlattice

The x-ray diffraction technique is used to measure the interdiffusion coefficients of a symmetrically strained Ge/Si superlattice consisting of alternating Ge and Si layers grown on a Ge_0.4Si_0.6 buffer layer. The buffer layer was 200 nm thick and was grown on a Si (100) substrate in order to symmetrize the strain, and thus maintain pseudomorphic growth of the superlattice. After the sample was annealed at different temperatures with various times, the interdiffusion coefficient D_λ was determined by monitoring the intensity decay of the low-angle x-ray diffraction peak resulting from the superlattice structure. The activation energy is calculated to be 3.1±0.2 eV in the annealing temperature range of 640-780°C.