ROUGHNESS ANALYSIS OF SI SIGE HETEROSTRUCTURES/

Atomic force microscopy is used to measure surface morphology of modul ation doped Si/SiGe heterostructures. Three components in the surface roughness are observed: mu m-scale roughness arising from misfit dislo cations formed to relieve strain, 1000-Angstrom-scale roughness believ ed to be associated with three-dimensional growth of the electron or h ole channel layers, and atomic-scale roughness with wavelengths of 10- 100 Angstrom. Detailed Fourier spectra of the roughness are obtained a nd used as input to a scattering computation for determining mobility. The results are compared with other mobility-limiting mechanisms, inc luding scattering from ionized impurities and from dislocations. (C) 1 995 American Vacuum Society.