Roughness analysis of Si/SiGe heterostructures

Atomic force microscopy is used to measure surface morphology of modulation doped Si/SiGe heterostructures. Three components in the surface roughness are observed: μm-scale roughness arising from misfit dislocations formed to relieve strain, 1000-Å-scale roughness believed to be associated with three-dimensional growth of the electron or hole channel layers, and atomic-scale roughness with wavelengths of 10–100 Å. Detailed Fourier spectra of the roughness are obtained and used as input to a scattering computation for determining mobility. The results are compared with other mobility-limiting mechanisms, including scattering from ionized impurities and from dislocations.