Enhanced Step Waviness on SiGe(001)-(2×1)Surfaces under Tensile Strain

Abstract

Scanning tunneling microscopy measurements of thermally cleaned, low Ge content SiGe(001) films under an $\sim 1\%$ biaxial tensile strain show large amplitude, quasiperiodic, thermally stable $S_B$-step undulations alternating with extremely straight $S_A$ steps on extended areas wherever the local step separation $L>\mathrm{}20\mathrm{}$ nm. The wavelength $\lambda$ scales roughly with $L^{1/2}$ for $20<L<\mathrm{}120\mathrm{}$ nm, and reaches a limiting value between 100 and 200 nm on larger terraces. The measured behavior suggests that the wavy steps are stabilized by surface stress relaxation effects which are enhanced by tensile strain.