Semiconductor Surface Roughness: Dependence on Sign and Magnitude of Bulk Strain

Abstract

Changes in surface roughness have been studied as a function of bulk compressive and tensile strains (biaxial in the plane of the sample surface) in thin films of compositionally uniform and dislocation-free ${\mathrm{Ge}}_{0.5}$ ${\mathrm{Si}}_{0.5}$. A pronounced surface roughness is observed only for films under compressive strains exceeding 1.4%. Molecular dynamics simulations show that this striking result has its origin in the strain-induced lowering of surface step free energies.