Residual strain in Ge films grown by surfactant-mediated epitaxy on Si(1 1 1) and Si(0 0 1) substrates

In this work, we investigated the residual strain in Ge films of varying thickness (50 nm–1 μm) grown by SME on Si(1 1 1) and Si(0 0 1). The in-plane and vertical lattice constants were measured by high-resolution X-ray diffraction recording reciprocal space maps of symmetrical and asymmetrical reflections. We observed a gradual decrease of residual strain with film thickness, that represents the respective equilibrium state for the relaxation of lattice mismatch induced strain and thermal strain caused by different thermal expansion of Ge and Si. The minimum thickness for full relaxation is found to be ∼260 nm on Si(1 1 1) and ∼140 nm on Si(0 0 1).